Publications of year 1998

Articles in journal or book chapters

1. Richard Bamler and Philipp Hartl. Synthetic Aperture Radar Interferometry. Inverse Problems, 14:1-54, August 1998. Keyword(s): Review Paper, SAR Processing, Interferometry, SAR Interferometry, differential SAR Interferometry, DInSAR, InSAR, deformation mapping, surface deformation, surface displacement, cartography, geodesy, geophysical techniques, radiowave interferometry, coherence.

   Abstract:

   Synthetic aperture radar (SAR) is a coherent active microwave imaging method. In remote sensing it is used for mapping the scattering properties of the Earth's surface in the respective wavelength domain. Many physical and geometric parameters of the imaged scene contribute to the grey value of a SAR image pixel. Scene inversion suffers from this high ambiguity and requires SAR data taken at different wavelength, polarization, time, incidence angle, etc. Interferometric SAR (InSAR) exploits the phase differences of at least two complex-valued SAR images acquired from different orbit positions and/or at different times. The information derived from these interferometric data sets can be used to measure several geophysical quantities, such as topography, deformations (volcanoes, earthquakes, ice fields), glacier flows, ocean currents, vegetation properties, etc. This paper reviews the technology and the signal theoretical aspects of InSAR. Emphasis is given to mathematical imaging models and the statistical properties of the involved quantities. Coherence is shown to be a useful concept for system description and for interferogram quality assessment. As a key step in InSAR signal processing two-dimensional phase unwrapping is discussed in detail. Several interferometric configurations are described and illustrated by real-world examples. A compilation of past, current and future InSAR systems concludes the paper.

   
   

   @Article{BamlerHartl98,
   author = {Richard Bamler and Philipp Hartl},
   journal = {Inverse Problems},
   title = {{Synthetic Aperture Radar Interferometry}},
   year = {1998},
   month = Aug,
   pages = {1-54},
   volume = {14},
   abstract = {Synthetic aperture radar (SAR) is a coherent active microwave imaging method. In remote sensing it is used for mapping the scattering properties of the Earth's surface in the respective wavelength domain. Many physical and geometric parameters of the imaged scene contribute to the grey value of a SAR image pixel. Scene inversion suffers from this high ambiguity and requires SAR data taken at different wavelength, polarization, time, incidence angle, etc. Interferometric SAR (InSAR) exploits the phase differences of at least two complex-valued SAR images acquired from different orbit positions and/or at different times. The information derived from these interferometric data sets can be used to measure several geophysical quantities, such as topography, deformations (volcanoes, earthquakes, ice fields), glacier flows, ocean currents, vegetation properties, etc. This paper reviews the technology and the signal theoretical aspects of InSAR. Emphasis is given to mathematical imaging models and the statistical properties of the involved quantities. Coherence is shown to be a useful concept for system description and for interferogram quality assessment. As a key step in InSAR signal processing two-dimensional phase unwrapping is discussed in detail. Several interferometric configurations are described and illustrated by real-world examples. A compilation of past, current and future InSAR systems concludes the paper.},
   comment = {++ very complete overview of InSAR},
   doi = {10.1088/0266-5611/14/4/001},
   file = {:BamlerHartl98.pdf:PDF},
   keywords = {Review Paper, SAR Processing, Interferometry, SAR Interferometry, differential SAR Interferometry, DInSAR, InSAR, deformation mapping, surface deformation, surface displacement, cartography;geodesy;geophysical techniques;radiowave interferometry; coherence},
   pdf = {../../../docs/BamlerHartl98.pdf},
   url = {http://iopscience.iop.org/article/10.1088/0266-5611/14/4/001},
   
   }
   




2. Hian Lim Chan and Tat Soon Yeo. Noniterative quality phase-gradient autofocus (QPGA) algorithm for spotlight SAR imagery. IEEE Trans. Geosci. Remote Sens., 36(5):1531-1539, September 1998. Keyword(s): SAR Processing, Autofocus, Phase Gradient Autofocus.

   Abstract:

   The phase-gradient autofocus (PGA) technique is robust over a wide range of imagery and phase error functions, but the convergence usually requires four-six iterations. It is necessarily iterative in an attempt to converge on a dominant target against clutter interference, while sufficiently capturing the blur function. In this paper, we propose to speed the estimation convergence by selectively increasing the pool of quality synchronization sources and not be limited by the range pixels of the SAR map. This is highly probable since each range bin contains more than one prominent scatterer across the integration aperture. It is also highly probable that the least-brightest selected scatterer in a range gate may turn out to be of higher energy as compared to the maximum brightest scatterer of another gate. With appropriate target filtering to final select the quality scatterers out of the large pool and with higher order phase error measurement tool, the new algorithm achieves near-convergence focusing quality without iteration. We named this solution the quality PGA (QPGA) algorithm.

   
   

   @Article{Chan1998,
   Title = {Noniterative quality phase-gradient autofocus {(QPGA)} algorithm for spotlight {SAR} imagery},
   Author = {Hian Lim Chan and Tat Soon Yeo},
   Month = sep,
   Number = {5},
   Pages = {1531--1539},
   Volume = {36},
   Year = {1998},
   Abstract = {The phase-gradient autofocus (PGA) technique is robust over a wide range of imagery and phase error functions, but the convergence usually requires four-six iterations. It is necessarily iterative in an attempt to converge on a dominant target against clutter interference, while sufficiently capturing the blur function. In this paper, we propose to speed the estimation convergence by selectively increasing the pool of quality synchronization sources and not be limited by the range pixels of the SAR map. This is highly probable since each range bin contains more than one prominent scatterer across the integration aperture. It is also highly probable that the least-brightest selected scatterer in a range gate may turn out to be of higher energy as compared to the maximum brightest scatterer of another gate. With appropriate target filtering to final select the quality scatterers out of the large pool and with higher order phase error measurement tool, the new algorithm achieves near-convergence focusing quality without iteration. We named this solution the quality PGA (QPGA) algorithm.},
   Journal = {IEEE Trans. Geosci. Remote Sens.},
   Keywords = {SAR Processing, Autofocus, Phase Gradient Autofocus},
   Owner = {ofrey},
   Pdf = {../../../docs/chanYeo98.pdf} 
   }
   




3. Hyeokho Choi and David C. Munson, Jr.. Direct-Fourier Reconstruction in Tomography and Synthetic Aperture Radar. International Journal of Imaging Systems and Technology, 9(1):1-13, 1998. Keyword(s): SAR Processing, Tomography, Computed Tomography, CT, Convolution Back-Projection, CBP, Direct-Fourier Image Reconstruction, DF, Interpolator, Fourier-Domain Interpolator.

   Abstract:

   We investigate the use of direct-Fourier (DF) image reconstruction in computed tomography and synthetic aperture radar (SAR). One of our aims is to determine why the convolution-backprojection (CBP) method is favored over DF methods in tomography, while DF methods are virtually always used in SAR. We show that the CBP algorithm is equivalent to DF reconstruction using a Jacobian-weighted two-dimensional periodic sinc-kernel interpolator. This interpolation is not optimal in any sense, which suggests that DF algorithms using optimal interpolators may surpass CBP in image quality. We consider use of two types of DF interpolation: a windowed sinc kernel, and the least-squares optimal Yen interpolator. Simulations show that reconstructions using the Yen interpolator do not possess the expected visual quality, because of regularization needed to preserve numerical stability. Next, we show that with a concentric-squares sampling scheme, DF interpolation can be performed accurately and efficiently, producing imagery that is superior to that obtainable by other algorithms. In the case of SAR, we show that the DF method performs very well with interpolators of low complexity. We also study DF reconstruction in SAR for trapezoidal grids. We conclude that the success of the DF method in SAR imaging is due to the nearly Cartesian shape of the sampling grid.

   
   

   @Article{choiMunson98:CTSAR,
   Title = {Direct-Fourier Reconstruction in Tomography and Synthetic Aperture Radar},
   Author = {Hyeokho Choi and David C. {Munson, Jr.}},
   Number = {1},
   Pages = {1--13},
   Url = {http://www3.interscience.wiley.com/cgi-bin/fulltext/37668/PDFSTART},
   Volume = {9},
   Year = {1998},
   Abstract = {We investigate the use of direct-Fourier (DF) image reconstruction in computed tomography and synthetic aperture radar (SAR). One of our aims is to determine why the convolution-backprojection (CBP) method is favored over DF methods in tomography, while DF methods are virtually always used in SAR. We show that the CBP algorithm is equivalent to DF reconstruction using a Jacobian-weighted two-dimensional periodic sinc-kernel interpolator. This interpolation is not optimal in any sense, which suggests that DF algorithms using optimal interpolators may surpass CBP in image quality. We consider use of two types of DF interpolation: a windowed sinc kernel, and the least-squares optimal Yen interpolator. Simulations show that reconstructions using the Yen interpolator do not possess the expected visual quality, because of regularization needed to preserve numerical stability. Next, we show that with a concentric-squares sampling scheme, DF interpolation can be performed accurately and efficiently, producing imagery that is superior to that obtainable by other algorithms. In the case of SAR, we show that the DF method performs very well with interpolators of low complexity. We also study DF reconstruction in SAR for trapezoidal grids. We conclude that the success of the DF method in SAR imaging is due to the nearly Cartesian shape of the sampling grid.},
   Journal = {International Journal of Imaging Systems and Technology},
   Keywords = {SAR Processing, Tomography, Computed Tomography, CT, Convolution Back-Projection, CBP, Direct-Fourier Image Reconstruction, DF, Interpolator, Fourier-Domain Interpolator},
   Owner = {ofrey},
   Pdf = {../../../docs/choiMunson98.pdf} 
   }
   




4. S.R. Cloude and Konstantinos P. Papathanassiou. Polarimetric SAR interferometry. IEEE Transactions on Geoscience and Remote Sensing, 36(5):1551-1565, September 1998. Keyword(s): SAR Processing, PolInSAR, geophysical techniques, radar imaging, radar polarimetry, radar theory, remote sensing by radar, synthetic aperture radarInSAR, coherence optimization problem, elevated forest canopy, general formulation, geophysical measurement technique, interferogram, interferometric SAR, interferometric coherence, land surface, linear combinations, maximization, polarimetric SAR interferometry, polarimetric basis transformation, radar remote sensing, scalar interferometry, stochastic scattering model, strong polarization dependency, synthetic aperture radar, terrain mapping, vector wave interferometry, SAR Tomography.

   Abstract:

   The authors examine the role of polarimetry in synthetic aperture radar (SAR) interferometry. They first propose a general formulation for vector wave interferometry that includes conventional scalar interferometry as a special case. Then, they show how polarimetric basis transformations can be introduced into SAR interferometry and applied to form interferograms between all possible linear combinations of polarization states. This allows them to reveal the strong polarization dependency of the interferometric coherence. They then solve the coherence optimization problem involving maximization of interferometric coherence and formulate a new coherent decomposition for polarimetric SAR interferometry that allows the separation of the effective phase centers of different scattering mechanisms. A simplified stochastic scattering model for an elevated forest canopy is introduced to demonstrate the effectiveness of the proposed algorithms. In this way, they demonstrate the importance of wave polarization for the physical interpretation of SAR interferograms. They investigate the potential of polarimetric SAR interferometry using results from the evaluation of fully polarimetric interferometric shuttle imaging radar (SIR)-C/X-SAR data collected during October 8-9, 1994, over the SE Baikal Lake Selenga delta region of Buriatia, Southeast Siberia, Russia

   
   

   @Article{cloudePapathanassiou1998:PolInSAR,
   author = {Cloude, S.R. and Papathanassiou, Konstantinos P.},
   journal = {IEEE Transactions on Geoscience and Remote Sensing},
   title = {Polarimetric {SAR} interferometry},
   year = {1998},
   issn = {0196-2892},
   month = {Sep},
   number = {5},
   pages = {1551-1565},
   volume = {36},
   abstract = {The authors examine the role of polarimetry in synthetic aperture radar (SAR) interferometry. They first propose a general formulation for vector wave interferometry that includes conventional scalar interferometry as a special case. Then, they show how polarimetric basis transformations can be introduced into SAR interferometry and applied to form interferograms between all possible linear combinations of polarization states. This allows them to reveal the strong polarization dependency of the interferometric coherence. They then solve the coherence optimization problem involving maximization of interferometric coherence and formulate a new coherent decomposition for polarimetric SAR interferometry that allows the separation of the effective phase centers of different scattering mechanisms. A simplified stochastic scattering model for an elevated forest canopy is introduced to demonstrate the effectiveness of the proposed algorithms. In this way, they demonstrate the importance of wave polarization for the physical interpretation of SAR interferograms. They investigate the potential of polarimetric SAR interferometry using results from the evaluation of fully polarimetric interferometric shuttle imaging radar (SIR)-C/X-SAR data collected during October 8-9, 1994, over the SE Baikal Lake Selenga delta region of Buriatia, Southeast Siberia, Russia},
   doi = {10.1109/36.718859},
   keywords = {SAR Processing, PolInSAR, geophysical techniques, radar imaging, radar polarimetry, radar theory, remote sensing by radar, synthetic aperture radarInSAR, coherence optimization problem, elevated forest canopy, general formulation, geophysical measurement technique, interferogram, interferometric SAR, interferometric coherence, land surface, linear combinations, maximization, polarimetric SAR interferometry, polarimetric basis transformation, radar remote sensing, scalar interferometry, stochastic scattering model, strong polarization dependency, synthetic aperture radar, terrain mapping, vector wave interferometry, SAR Tomography},
   owner = {ofrey},
   pdf = {../../../docs/cloudePapathanassiou1998.pdf},
   url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=718859&isnumber=15531},
   
   }
   




5. Mario Costantini. A novel phase unwrapping method based on network programming. IEEE Trans. Geosci. Remote Sens., 36(3):813-821, May 1998. Keyword(s): SAR Processsing, phase unwrapping, SAR Interferometry, InSAR, SAR, geophysical signal processing, geophysical techniques, radar imaging, remote sensing by radar, synthetic aperture radar, SAR interferometry, function reconstruction, geophysical measurement technique, global minimization problem, interferometric SAR, land surface, neighboring pixel, network programming, network structure, phase difference, phase unwrapping method, radar imaging, radar remote sensing, synthetic aperture radar, terrain mapping, Costs, Fast Fourier transforms, Functional programming, Interferometry, Performance evaluation, Phase estimation, Robustness, Synthetic aperture radar, Testing, Two dimensional displays.

   Abstract:

   Phase unwrapping is the reconstruction of a function on a grid given its values mod 2 pi. Phase unwrapping is a key problem in all quantitative applications of synthetic aperture radar (SAR) interferometry, but also in other fields. A new phase unwrapping method, which is a different approach from existing techniques, is described and tested. The method starts from the fact that the phase differences of neighboring pixels can be estimated with a potential error that is an integer multiple of 2 pi. This suggests the formulation of the phase unwrapping problem as a global minimization problem with integer variables. Recognizing the network structure underlying the problem makes for an efficient solution. In fact, it is possible to equate the phase unwrapping problem to the problem of finding the minimum cost flow on a network, for the solution of which there exist very efficient techniques. The tests performed on real and simulated interferometric SAR data confirm the validity of the approach

   
   

   @Article{costantiniTGRS1998PhaseUnwrappingNetworkProgramming,
   author = {Mario Costantini},
   title = {A novel phase unwrapping method based on network programming},
   journal = {IEEE Trans. Geosci. Remote Sens.},
   year = {1998},
   volume = {36},
   number = {3},
   pages = {813-821},
   month = may,
   issn = {0196-2892},
   abstract = {Phase unwrapping is the reconstruction of a function on a grid given its values mod 2 pi. Phase unwrapping is a key problem in all quantitative applications of synthetic aperture radar (SAR) interferometry, but also in other fields. A new phase unwrapping method, which is a different approach from existing techniques, is described and tested. The method starts from the fact that the phase differences of neighboring pixels can be estimated with a potential error that is an integer multiple of 2 pi. This suggests the formulation of the phase unwrapping problem as a global minimization problem with integer variables. Recognizing the network structure underlying the problem makes for an efficient solution. In fact, it is possible to equate the phase unwrapping problem to the problem of finding the minimum cost flow on a network, for the solution of which there exist very efficient techniques. The tests performed on real and simulated interferometric SAR data confirm the validity of the approach},
   doi = {10.1109/36.673674},
   keywords = {SAR Processsing, phase unwrapping, SAR Interferometry, InSAR, SAR, geophysical signal processing;geophysical techniques;radar imaging;remote sensing by radar;synthetic aperture radar;SAR interferometry;function reconstruction;geophysical measurement technique;global minimization problem;interferometric SAR;land surface;neighboring pixel;network programming;network structure;phase difference;phase unwrapping method;radar imaging;radar remote sensing;synthetic aperture radar;terrain mapping;Costs;Fast Fourier transforms;Functional programming;Interferometry;Performance evaluation;Phase estimation;Robustness;Synthetic aperture radar;Testing;Two dimensional displays},
   owner = {ofrey},
   
   }
   




6. Stuart R. DeGraaf. SAR imaging via modern 2-D spectral estimation methods. Image Processing, IEEE Transactions on, 7(5):729-761, 1998. Keyword(s): SAR Processing, Spectral Estimation, adaptive estimation, adaptive signal processing, estimation theory, image resolution, interference suppression, radar imaging, radar interference, radiowave interferometry, speckle, spectral analysis, synthetic aperture radar, 2-D spectral estimation methods, ASR, MVM, RRMVM, SVA, adaptive SAR imaging, adaptive nulling, adaptive sidelobe reduction, adaptive spectral estimation, averaging, height estimates, interferometric height, minimum variance method, multichannel variants, polarimetric displaced-aperture interferometric data, power spectrum estimation methods, reduced-rank MVM, reflectivity intensity, resolution, scattering intensity, sidelobe artifacts, space variant apodization, synthetic aperture radar imaging, MUSIC.

   Abstract:

   Discusses the use of modern 2D spectral estimation algorithms forsynthetic aperture radar (SAR) imaging. The motivation for applyingpower spectrum estimation methods to SAR imaging is to improveresolution, remove sidelobe artifacts, and reduce speckle compared towhat is possible with conventional Fourier transform SAR imagingtechniques. This paper makes two principal contributions to the field ofadaptive SAR imaging. First, it is a comprehensive comparison of 2Dspectral estimation methods for SAR imaging. It provides a synopsis ofthe algorithms available, discusses their relative merits for SARimaging, and illustrates their performance on simulated and collectedSAR imagery. Some of the algorithms presented or their derivations arenew, as are some of the insights into or analyses of the algorithms.Second, this work develops multichannel variants of four relatedalgorithms, minimum variance method (MVM), reduced-rank MVM (RRMVM),adaptive sidelobe reduction (ASR) and space variant apodization (SVA) toestimate both reflectivity intensity and interferometric height frompolarimetric displaced-aperture interferometric data. All of theseinterferometric variants are new. In the interferometric contest,adaptive spectral estimation can improve the height estimates through acombination of adaptive nulling and averaging. Examples illustrate thatMVM, ASR, and SVA offer significant advantages over Fourier methods forestimating both scattering intensity and interferometric height, andallow empirical comparison of the accuracies of Fourier, MVM, ASR, andSVA interferometric height estimates

   
   

   @Article{deGraaf98ModernSpectralEstim,
   author = {DeGraaf, Stuart R.},
   journal = {Image Processing, IEEE Transactions on},
   title = {SAR imaging via modern 2-D spectral estimation methods},
   year = {1998},
   issn = {1057-7149},
   number = {5},
   pages = {729--761},
   volume = {7},
   abstract = {Discusses the use of modern 2D spectral estimation algorithms forsynthetic aperture radar (SAR) imaging. The motivation for applyingpower spectrum estimation methods to SAR imaging is to improveresolution, remove sidelobe artifacts, and reduce speckle compared towhat is possible with conventional Fourier transform SAR imagingtechniques. This paper makes two principal contributions to the field ofadaptive SAR imaging. First, it is a comprehensive comparison of 2Dspectral estimation methods for SAR imaging. It provides a synopsis ofthe algorithms available, discusses their relative merits for SARimaging, and illustrates their performance on simulated and collectedSAR imagery. Some of the algorithms presented or their derivations arenew, as are some of the insights into or analyses of the algorithms.Second, this work develops multichannel variants of four relatedalgorithms, minimum variance method (MVM), reduced-rank MVM (RRMVM),adaptive sidelobe reduction (ASR) and space variant apodization (SVA) toestimate both reflectivity intensity and interferometric height frompolarimetric displaced-aperture interferometric data. All of theseinterferometric variants are new. In the interferometric contest,adaptive spectral estimation can improve the height estimates through acombination of adaptive nulling and averaging. Examples illustrate thatMVM, ASR, and SVA offer significant advantages over Fourier methods forestimating both scattering intensity and interferometric height, andallow empirical comparison of the accuracies of Fourier, MVM, ASR, andSVA interferometric height estimates},
   file = {:deGraaf98ModernSpectralEstim.pdf:PDF},
   keywords = {SAR Processing, Spectral Estimation, adaptive estimation, adaptive signal processing, estimation theory, image resolution, interference suppression, radar imaging, radar interference, radiowave interferometry, speckle, spectral analysis, synthetic aperture radar, 2-D spectral estimation methods, ASR, MVM, RRMVM, SVA, adaptive SAR imaging, adaptive nulling, adaptive sidelobe reduction, adaptive spectral estimation, averaging, height estimates, interferometric height, minimum variance method, multichannel variants, polarimetric displaced-aperture interferometric data, power spectrum estimation methods, reduced-rank MVM, reflectivity intensity, resolution, scattering intensity, sidelobe artifacts, space variant apodization, synthetic aperture radar imaging, MUSIC},
   owner = {ofrey},
   pdf = {../../../docs/deGraaf98.pdf},
   timestamp = {2006.03.24},
   url = {http://ieeexplore.ieee.org/iel4/83/14624/00668029.pdf},
   
   }
   




7. Knut Eldhuset. A new fourth-order processing algorithm for spaceborne SAR. Aerospace and Electronic Systems, IEEE Transactions on, 34(3):824-835, 1998. Keyword(s): SAR Processing, digital simulation, radar theory, signal processing, spaceborne radar, synthetic aperture radar, transfer functions, azimuth lines, extended ETF, fourth-order EETF, fourth-order processing algorithm, fourth-order signal aperture radar, high quality images, integration times, phase corrections, phase preservation, range-variant phase corrections, satellite-Earth relative motion, spaceborne SAR, spatial resolution, two-dimensional exact transfer function.

   Abstract:

   A new fourth-order signal aperture radar (SAR) processingalgorithm has been developed for a general satellite-Earth relativemotion. The two-dimensional exact transfer function (ETF) is calculatedand range-variant phase corrections have been calculated in order toprocess many azimuth lines per block. The ETF together with the phasecorrections has been called the fourth-order EETF (extended ETF). It isalso shown that a fourth-order EETF is necessary to process high qualityimages from spaceborne SAR with long integration times with spatialresolution around 1 m. The algorithm is fast and is anticipated to havegood phase preservation properties

   
   

   @Article{eldhuset98:EETF,
   author = {Eldhuset, Knut},
   journal = {Aerospace and Electronic Systems, IEEE Transactions on},
   title = {A new fourth-order processing algorithm for spaceborne SAR},
   year = {1998},
   number = {3},
   pages = {824--835},
   volume = {34},
   abstract = {A new fourth-order signal aperture radar (SAR) processingalgorithm has been developed for a general satellite-Earth relativemotion. The two-dimensional exact transfer function (ETF) is calculatedand range-variant phase corrections have been calculated in order toprocess many azimuth lines per block. The ETF together with the phasecorrections has been called the fourth-order EETF (extended ETF). It isalso shown that a fourth-order EETF is necessary to process high qualityimages from spaceborne SAR with long integration times with spatialresolution around 1 m. The algorithm is fast and is anticipated to havegood phase preservation properties},
   keywords = {SAR Processing, digital simulation, radar theory, signal processing, spaceborne radar, synthetic aperture radar, transfer functions, azimuth lines, extended ETF, fourth-order EETF, fourth-order processing algorithm, fourth-order signal aperture radar, high quality images, integration times, phase corrections, phase preservation, range-variant phase corrections, satellite-Earth relative motion, spaceborne SAR, spatial resolution, two-dimensional exact transfer function},
   owner = {ofrey},
   pdf = {../../../docs/eldhuset98.pdf},
   timestamp = {2006.03.24},
   url = {http://ieeexplore.ieee.org/iel4/7/15279/00705890.pdf},
   
   }
   




8. Giorgio Franceschetti, Antonio Iodice, Maurizio Migliaccio, and Daniele Riccio. A Novel Across-Track SAR Interferometry Simulator. IEEE Transactions on Geoscience and Remote Sensing, 36(3):950-962, May 1998. Keyword(s): SAR Processing, Simulation, SAR Simulator, Raw Data Simulator, Interferometry, Interferometry Simulator.

   Abstract:

   A novel across-track interferometric synthetic aperture radar (SAR) raw signal simulator is presented. It is based on an electromagnetic backscattering model of the scene and an accurate description of the SAR system impulse response function. A set of meaningful examples are also presented. They show that the proposed simulator is structurally consistent and correctly simulates the decorrelation effect, both in the mean and in the distribution sense.

   
   

   @Article{francescIodMigliaRic98:Simulation,
   Title = {{A Novel Across-Track SAR Interferometry Simulator}},
   Author = {Giorgio Franceschetti and Antonio Iodice and Maurizio Migliaccio and Daniele Riccio},
   Month = May,
   Number = {3},
   Pages = {950-962},
   Url = {http://ieeexplore.ieee.org/iel4/36/14800/00673686.pdf},
   Volume = {36},
   Year = {1998},
   Abstract = {A novel across-track interferometric synthetic aperture radar (SAR) raw signal simulator is presented. It is based on an electromagnetic backscattering model of the scene and an accurate description of the SAR system impulse response function. A set of meaningful examples are also presented. They show that the proposed simulator is structurally consistent and correctly simulates the decorrelation effect, both in the mean and in the distribution sense.},
   Journal = {IEEE Transactions on Geoscience and Remote Sensing},
   Keywords = {SAR Processing, Simulation, SAR Simulator, Raw Data Simulator, Interferometry, Interferometry Simulator},
   Pdf = {../../../docs/francescIodMigliaRic98.pdf} 
   }
   




9. Anthony Freeman and Stephen L. Durden. A three-component scattering model for polarimetric SAR data. IEEE Trans. Geosci. Remote Sens., 36(3):963-973, May 1998. Keyword(s): SAR Processing, Polarimetric Decomposition, Freeman-Durden Decomposition, Bragg scatter, backscatter, canopy scatter, composite scattering model, double-bounce scatter, flooding, forest, geophysical measurement technique, inundation, land surface, orthogonal surface, polarimetric SAR, radar polarimetry, radar remote sensing, radar scattering, randomly oriented dipoles, rough surface, synthetic aperture radar, terrain mapping, three-component scattering model, tropical rain forest, vegetation mapping, backscatter, forestry, geophysical techniques, radar cross-sections, radar polarimetry, radar theory, remote sensing by radar, synthetic aperture radar;.

   Abstract:

   An approach has been developed that involves the fit of a combination of three simple scattering mechanisms to polarimetric SAR observations. The mechanisms are canopy scatter from a cloud of randomly oriented dipoles, evenor double-bounce scatter from a pair of orthogonal surfaces with different dielectric constants and Bragg scatter from a moderately rough surface. This composite scattering model is used to describe the polarimetric backscatter from naturally occurring scatterers. The model is shown to describe the behavior of polarimetric backscatter from tropical rain forests quite well by applying it to data from NASA/Jet Propulsion Laboratory's (JPLs) airborne polarimetric synthetic aperture radar (AIRSAR) system. The model fit allows clear discrimination between flooded and nonflooded forest and between forested and deforested areas, for example. The model is also shown to be usable as a predictive tool to estimate the effects of forest inundation and disturbance on the fully polarimetric radar signature. An advantage of this model fit approach is that the scattering contributions from the three basic scattering mechanisms can be estimated for clusters of pixels in polarimetric SAR images. Furthermore, it is shown that the contributions of the three scattering mechanisms to the HH, HV, and VV backscatter can be calculated from the model fit. Finally, this model fit approach is justified as a simplification of more complicated scattering models, which require many inputs to solve the forward scattering problem

   
   

   @Article{freemanDurden1998:PolDecomp,
   Title = {A three-component scattering model for polarimetric {SAR} data},
   Author = {Freeman, Anthony and Durden, Stephen L.},
   Doi = {10.1109/36.673687},
   ISSN = {0196-2892},
   Month = may,
   Number = {3},
   Pages = {963-973},
   Volume = {36},
   Year = {1998},
   Abstract = {An approach has been developed that involves the fit of a combination of three simple scattering mechanisms to polarimetric SAR observations. The mechanisms are canopy scatter from a cloud of randomly oriented dipoles, evenor double-bounce scatter from a pair of orthogonal surfaces with different dielectric constants and Bragg scatter from a moderately rough surface. This composite scattering model is used to describe the polarimetric backscatter from naturally occurring scatterers. The model is shown to describe the behavior of polarimetric backscatter from tropical rain forests quite well by applying it to data from NASA/Jet Propulsion Laboratory's (JPLs) airborne polarimetric synthetic aperture radar (AIRSAR) system. The model fit allows clear discrimination between flooded and nonflooded forest and between forested and deforested areas, for example. The model is also shown to be usable as a predictive tool to estimate the effects of forest inundation and disturbance on the fully polarimetric radar signature. An advantage of this model fit approach is that the scattering contributions from the three basic scattering mechanisms can be estimated for clusters of pixels in polarimetric SAR images. Furthermore, it is shown that the contributions of the three scattering mechanisms to the HH, HV, and VV backscatter can be calculated from the model fit. Finally, this model fit approach is justified as a simplification of more complicated scattering models, which require many inputs to solve the forward scattering problem},
   Journal = {IEEE Trans. Geosci. Remote Sens.},
   Keywords = {SAR Processing, Polarimetric Decomposition, Freeman-Durden Decomposition, Bragg scatter;backscatter;canopy scatter;composite scattering model;double-bounce scatter;flooding;forest;geophysical measurement technique;inundation;land surface;orthogonal surface;polarimetric SAR;radar polarimetry;radar remote sensing;radar scattering;randomly oriented dipoles;rough surface;synthetic aperture radar;terrain mapping;three-component scattering model;tropical rain forest;vegetation mapping;backscatter;forestry;geophysical techniques;radar cross-sections;radar polarimetry;radar theory;remote sensing by radar;synthetic aperture radar;},
   Pdf = {../../../docs/freemanDurden1998.pdf} 
   }
   




10. Richard M. Goldstein and Charles L. Werner. Radar interferogram filtering for geophysical applications. Geophysical Research Letters, 25(21):4035-4038, 1998. Keyword(s): SAR Processing, SAR Interferometry, Interferometry, Goldstein-Werner filter, adaptive filter, adaptive interferogram filtering.

    Abstract:

    The use of SAR interferometry is often impeded by decorrelation from thermal noise, temporal change, and baseline geometry. Power spectra of interferograms are typically the sum of a narrow-band component combined with broad-band noise. We describe a new adaptive filtering algorithm that dramatically lowers phase noise, improving both measurement accuracy and phase unwrapping, while demonstrating graceful degradation in regions of pure noise. The performance of the filter is demonstrated with SAR data from the ERS satellites over the Jakobshavns glacier of Greenland.

    
    

    @Article{goldsteinWernerGRL1998GoldsteinWernerFilterInSAR,
    author = {Goldstein, Richard M. and Werner, Charles L.},
    title = {Radar interferogram filtering for geophysical applications},
    journal = {Geophysical Research Letters},
    year = {1998},
    volume = {25},
    number = {21},
    pages = {4035-4038},
    abstract = {The use of SAR interferometry is often impeded by decorrelation from thermal noise, temporal change, and baseline geometry. Power spectra of interferograms are typically the sum of a narrow-band component combined with broad-band noise. We describe a new adaptive filtering algorithm that dramatically lowers phase noise, improving both measurement accuracy and phase unwrapping, while demonstrating graceful degradation in regions of pure noise. The performance of the filter is demonstrated with SAR data from the ERS satellites over the Jakobshavns glacier of Greenland.},
    doi = {10.1029/1998GL900033},
    eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1998GL900033},
    file = {:goldsteinWernerGRL1998GoldsteinWernerFilterInSAR.pdf:PDF},
    keywords = {SAR Processing, SAR Interferometry, Interferometry, Goldstein-Werner filter, adaptive filter, adaptive interferogram filtering},
    owner = {ofrey},
    url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/1998GL900033},
    
    }
    




11. Aruna Gunawardena and Dennis Longstaff. Wave Equation Formulation of Synthetic Aperture Radar (SAR) Algorithms in the Time-Space Domain. IEEE Transactions on Geoscience and Remote Sensing, 36(6):1995-1999, November 1998. Keyword(s): SAR Processing, Time-Space Domain Algorithm, Wavenumber Domain Algorithm, omega-k, Range Migration Algorithm, Comparison of Algorithms.

    Abstract:

    In this paper, we propose an alternative wave equationbased time-space domain synthetic aperture radar (SAR) algorithm. The proposed algorithm can be interpreted as the exact time-space domain counterpart of the wave equation-based omega-k domain SAR algorithms proposed in recent years. Links to conventional SAR and seismic migration algorithm are also established.

    
    

    @Article{gunawardenaLongstaff98:SAR,
    Title = {{Wave Equation Formulation of Synthetic Aperture Radar (SAR) Algorithms in the Time-Space Domain}},
    Author = {Aruna Gunawardena and Dennis Longstaff},
    Month = Nov,
    Number = {6},
    Pages = {1995-1999},
    Url = {http://ieeexplore.ieee.org/iel4/36/15714/00729376.pdf},
    Volume = {36},
    Year = {1998},
    Abstract = {In this paper, we propose an alternative wave equationbased time-space domain synthetic aperture radar (SAR) algorithm. The proposed algorithm can be interpreted as the exact time-space domain counterpart of the wave equation-based omega-k domain SAR algorithms proposed in recent years. Links to conventional SAR and seismic migration algorithm are also established.},
    Journal = {IEEE Transactions on Geoscience and Remote Sensing},
    Keywords = {SAR Processing, Time-Space Domain Algorithm, Wavenumber Domain Algorithm, omega-k, Range Migration Algorithm, Comparison of Algorithms},
    Pdf = {../../../docs/gunawardenaLongstaff98.pdf} 
    }
    




12. R. Lanari, S. Hensley, and P.A. Rosen. Chirp z-transform based SPECAN approach for phase-preserving ScanSAR image generation. Radar, Sonar and Navigation, IEE Proceedings -, 145(5):254-261, October 1998. Keyword(s): SAR Processing, Modified SPECAN, SPECAN, Spectral Analysis, Z transforms, airborne radar, image resolution, radar imaging, radar resolution, InSAR, SAR Interferometry, radiowave interferometry, spaceborne radar, synthetic aperture radar, time-domain analysis, transient response, ScanSAR, airborne platform, algorithm, azimuth focusing, chirp z-transform, chirp-z, experiments, high resolution microwave images, image impulse response, interferometric ScanSAR systems, modified SPECAN algorithm, phase analysis, phase-preserving ScanSAR image generation, real data, scan mode synthetic aperture radar, simulated data, spaceborne platform, standard range-Doppler approach, time domain.

    Abstract:

    The scan mode synthetic aperture radar (ScanSAR) image impulse response is derived in the time domain, and particular attention is given to the analysis of the phase, which is important for several applications, and especially in interferometric ScanSAR systems. A new algorithm for phase-preserving azimuth focusing of ScanSAR data, that extends the basic SPECAN procedure, is presented. The proposed algorithm avoids the interpolation step needed to achieve a constant azimuth pixel spacing by replacing the standard Fourier transform used in the SPECAN procedure with an appropriate chirp z-transform. The relationship between the modified SPECAN algorithm and the standard range-Doppler approach is also discussed. Experiments on real and simulated data are carried out to validate the theory

    
    

    @Article{lanariHensleyRosen1998Long:ModifiedSPECAN,
    author = {Lanari, R. and Hensley, S. and Rosen, P.A.},
    journal = {Radar, Sonar and Navigation, IEE Proceedings -},
    title = {Chirp z-transform based SPECAN approach for phase-preserving ScanSAR image generation},
    year = {1998},
    issn = {1350-2395},
    month = {Oct},
    number = {5},
    pages = {254-261},
    volume = {145},
    abstract = {The scan mode synthetic aperture radar (ScanSAR) image impulse response is derived in the time domain, and particular attention is given to the analysis of the phase, which is important for several applications, and especially in interferometric ScanSAR systems. A new algorithm for phase-preserving azimuth focusing of ScanSAR data, that extends the basic SPECAN procedure, is presented. The proposed algorithm avoids the interpolation step needed to achieve a constant azimuth pixel spacing by replacing the standard Fourier transform used in the SPECAN procedure with an appropriate chirp z-transform. The relationship between the modified SPECAN algorithm and the standard range-Doppler approach is also discussed. Experiments on real and simulated data are carried out to validate the theory},
    file = {:lanariHensleyRosen1998Long.pdf:PDF},
    keywords = {SAR Processing, Modified SPECAN, SPECAN, Spectral Analysis, Z transforms, airborne radar, image resolution, radar imaging, radar resolution, InSAR, SAR Interferometry, radiowave interferometry, spaceborne radar, synthetic aperture radar, time-domain analysis, transient response, ScanSAR, airborne platform, algorithm, azimuth focusing, chirp z-transform, chirp-z, experiments, high resolution microwave images, image impulse response, interferometric ScanSAR systems, modified SPECAN algorithm, phase analysis, phase-preserving ScanSAR image generation, real data, scan mode synthetic aperture radar, simulated data, spaceborne platform, standard range-Doppler approach, time domain},
    owner = {ofrey},
    pdf = {../../../docs/lanariHensleyRosen1998Long.pdf},
    url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=741980&isnumber=15932},
    
    }
    




13. Zheng-She Liu and Jian Li. Synthetic-aperture-radar motion compensation and feature extraction by means of a relaxation-based algorithm. J. Opt. Soc. Am. A, 15(3):599-610, 1998. Keyword(s): SAR Processing, Autofocus, Motion Compensation, MoComp, Residual Motion Errors, Airborne SAR, Phase Gradient Autofocus, PGA, RELAX, MCRELAX, Cramer-Rao Bound, Parametric Estimation.
    

    @Article{liuLi98:Autofocus,
    Title = {Synthetic-aperture-radar motion compensation and feature extraction by means of a relaxation-based algorithm},
    Author = {Zheng-She Liu and Jian Li},
    Number = {3},
    Pages = {599--610},
    Url = {http://www.opticsinfobase.org/DirectPDFAccess/6D59F34F-BDB9-137E-C70AC82BCFBCC953_1422.pdf},
    Volume = {15},
    Year = {1998},
    Journal = {J. Opt. Soc. Am. A},
    Keywords = {SAR Processing, Autofocus, Motion Compensation, MoComp, Residual Motion Errors, Airborne SAR, Phase Gradient Autofocus, PGA, RELAX, MCRELAX, Cramer-Rao Bound, Parametric Estimation},
    Pdf = {../../../docs/liuLi98.pdf},
    Publisher = {OSA} 
    }
    




14. Zheng-She Liu, Hongbin Li, and Jian Li. Efficient implementation of Capon and APES for spectral estimation. IEEE Transactions on Aerospace and Electronic Systems, 34(4):1314-1319, October 1998. Keyword(s): Capon, MVDR, minimum variance distortionless reponse, spectral analysis, adaptive estimation, adaptive filters, matched filters, statistical analysis, filtering theory, Capon, APES, spectral estimation, matched-filterbank spectral estimators, narrow spectral peaks, sidelobe levels, statistical performance, Finite impulse response filter, Frequency, Fast Fourier transforms, Two dimensional displays, Application software, Synthetic aperture radar, Adaptive filters, Filtering, Noise level, Interference.

    Abstract:

    Both the Capon and APES estimators can be shown to belong to the class of matched-filterbank spectral estimators and can be used to obtain complex spectral estimates that have more narrow spectral peaks and lower sidelobe levels than the fast Fourier transform (FFT) methods. It can also be shown that APES has better statistical performance than Capon. In this paper, we address the issue of how to efficiently implement Capon and APES for spectral estimation.

    
    

    @Article{liuLiLiTAES1998EffientCaponAndAPESforSpectralEstimation,
    author = {Zheng-She Liu and Hongbin Li and Jian Li},
    title = {Efficient implementation of {Capon} and {APES} for spectral estimation},
    journal = {IEEE Transactions on Aerospace and Electronic Systems},
    year = {1998},
    volume = {34},
    number = {4},
    pages = {1314-1319},
    month = {Oct},
    issn = {2371-9877},
    abstract = {Both the Capon and APES estimators can be shown to belong to the class of matched-filterbank spectral estimators and can be used to obtain complex spectral estimates that have more narrow spectral peaks and lower sidelobe levels than the fast Fourier transform (FFT) methods. It can also be shown that APES has better statistical performance than Capon. In this paper, we address the issue of how to efficiently implement Capon and APES for spectral estimation.},
    doi = {10.1109/7.722716},
    file = {:liuLiLiTAES1998EffientCaponAndAPESforSpectralEstimation.pdf:PDF},
    keywords = {Capon, MVDR, minimum variance distortionless reponse, spectral analysis;adaptive estimation;adaptive filters;matched filters;statistical analysis;filtering theory;Capon;APES;spectral estimation;matched-filterbank spectral estimators;narrow spectral peaks;sidelobe levels;statistical performance;Finite impulse response filter;Frequency;Fast Fourier transforms;Two dimensional displays;Application software;Synthetic aperture radar;Adaptive filters;Filtering;Noise level;Interference},
    owner = {ofrey},
    
    }
    




15. Didier Massonnet and Kurt L. Feigl. Radar interferometry and its application to changes in the Earth's surface. Reviews of Geophysics, 36(4):441-500, 1998. Keyword(s): Permeability and porosity.

    Abstract:

    Geophysical applications of radar interferometry to measure changes in the Earth's surface have exploded in the early 1990s. This new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times. The resulting interferogram is a contour map of the change in distance between the ground and the radar instrument. These maps provide an unsurpassed spatial sampling density (100 pixels/km), a competitive precision (1 cm), and a useful observation cadence (1 pass /month). They record movements in the crust, perturbations in the atmosphere, dielectric modifications in the soil, and relief in the topography. They are also sensitive to technical effects, such as relative variations in the radar's trajectory or variations in its frequency standard. We describe how all these phenomena contribute to an interferogram. Then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments, including the four satellites currently in orbit: ERS-1, ERS-2, JERS-1, and RADARSAT. The next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement: respecting the limits of the technique, assessing its uncertainty, recognizing artifacts, and discriminating different types of signal. We then review the geophysical applications published to date, most of which study deformation related to earthquakes, volcanoes, and glaciers using ERS-1 data. We also show examples of monitoring natural hazards and environmental alterations related to landslides, subsidence, and agriculture. In addition, we consider subtler geophysical signals such as postseismic relaxation, tidal loading of coastal areas, and interseismic strain accumulation. We conclude with our perspectives on the future of radar interferometry. The objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it.

    
    

    @Article{massonnetFeiglReviewsGeophysics1998DINSARReviewPaper,
    author = {Massonnet, Didier and Feigl, Kurt L.},
    title = {Radar interferometry and its application to changes in the {E}arth's surface},
    journal = {Reviews of Geophysics},
    year = {1998},
    volume = {36},
    number = {4},
    pages = {441-500},
    issn = {1944-9208},
    abstract = {Geophysical applications of radar interferometry to measure changes in the Earth's surface have exploded in the early 1990s. This new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times. The resulting interferogram is a contour map of the change in distance between the ground and the radar instrument. These maps provide an unsurpassed spatial sampling density (100 pixels/km), a competitive precision (1 cm), and a useful observation cadence (1 pass /month). They record movements in the crust, perturbations in the atmosphere, dielectric modifications in the soil, and relief in the topography. They are also sensitive to technical effects, such as relative variations in the radar's trajectory or variations in its frequency standard. We describe how all these phenomena contribute to an interferogram. Then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments, including the four satellites currently in orbit: ERS-1, ERS-2, JERS-1, and RADARSAT. The next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement: respecting the limits of the technique, assessing its uncertainty, recognizing artifacts, and discriminating different types of signal. We then review the geophysical applications published to date, most of which study deformation related to earthquakes, volcanoes, and glaciers using ERS-1 data. We also show examples of monitoring natural hazards and environmental alterations related to landslides, subsidence, and agriculture. In addition, we consider subtler geophysical signals such as postseismic relaxation, tidal loading of coastal areas, and interseismic strain accumulation. We conclude with our perspectives on the future of radar interferometry. The objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it.},
    doi = {10.1029/97RG03139},
    file = {:massonnetFeiglReviewsGeophysics1998DINSARReviewPaper.pdf:PDF},
    keywords = {Permeability and porosity},
    pdf = {../../../docs/massonnetFeiglReviewsGeophysics1998DINSARReviewPaper.pdf},
    url = {http://dx.doi.org/10.1029/97RG03139},
    
    }
    




16. Christian Matzler. Improved Born approximation for scattering of radiation in a granular medium. Journal of Applied Physics, 83(11):6111-6117, 1998.
    

    @Article{Maetzler1998,
    author = {Matzler, Christian},
    title = {Improved Born approximation for scattering of radiation in a granular medium},
    journal = {Journal of Applied Physics},
    year = {1998},
    volume = {83},
    number = {11},
    pages = {6111--6117},
    owner = {ofrey},
    publisher = {AIP},
    
    }
    




17. Johan J. Mohr, Niels Reeh, and Soren N. Madsen. Three-dimensional glacial flow and surface elevation measured with radar interferometry. Nature, 391(6664):273-276, January 1998. Keyword(s): SAR Processing, Interferometry, SAR interferometry, differential SAR interferometry, DInSAR, Glacier velocity, glacial flow.

    Abstract:

    Outlet glaciers which serve to drain ice from ice sheets, seem to be dynamically less stable in North Greenland than in South Greenland. Storstrommen, a large outlet glacier in northeastern Greenland which surged between 1978 and 1984, has been well studied. In general, neither glacier surge mechanisms nor the geographical distribution of the surges are well known. Conventional satellite radar interferometry can provide large-scale topography models with high resolution, and can measure the radar line-of-sight component of ice-flow vectors5, but cannot map full vector flow fields. Here we present an interferometry method that combines observations from descending and ascending satellite orbits which, assuming ice flow parallel to the topographic surface, allows us to use the differing view angles to estimate full three-dimensional surface flow patterns. The accuracy of our technique is confirmed by the good agreement between our radar-based flow model and in situ Global Positioning System (GPS) reference data at Storstrommen. Radar measurements such as these, made regularly and at high spatial density, have the potential to substantially enhance our understanding of glacier dynamics and ice-sheet flow, as well as improve the accuracy of glacier mass-balance estimates.

    
    

    @Article{mohrReehMadsenNature1998InSARGlacierFlowAndDEM,
    author = {Mohr, Johan J. and Reeh, Niels and Madsen, Soren N.},
    journal = {Nature},
    title = {Three-dimensional glacial flow and surface elevation measured with radar interferometry},
    year = {1998},
    issn = {0028-0836},
    month = jan,
    number = {6664},
    pages = {273-276},
    volume = {391},
    abstract = {Outlet glaciers which serve to drain ice from ice sheets, seem to be dynamically less stable in North Greenland than in South Greenland. Storstrommen, a large outlet glacier in northeastern Greenland which surged between 1978 and 1984, has been well studied. In general, neither glacier surge mechanisms nor the geographical distribution of the surges are well known. Conventional satellite radar interferometry can provide large-scale topography models with high resolution, and can measure the radar line-of-sight component of ice-flow vectors5, but cannot map full vector flow fields. Here we present an interferometry method that combines observations from descending and ascending satellite orbits which, assuming ice flow parallel to the topographic surface, allows us to use the differing view angles to estimate full three-dimensional surface flow patterns. The accuracy of our technique is confirmed by the good agreement between our radar-based flow model and in situ Global Positioning System (GPS) reference data at Storstrommen. Radar measurements such as these, made regularly and at high spatial density, have the potential to substantially enhance our understanding of glacier dynamics and ice-sheet flow, as well as improve the accuracy of glacier mass-balance estimates.},
    doi = {10.1038/34635},
    file = {:mohrReehMadsenNature1998InSARGlacierFlowAndDEM.pdf:PDF},
    keywords = {SAR Processing, Interferometry, SAR interferometry, differential SAR interferometry, DInSAR, Glacier velocity, glacial flow},
    owner = {ofrey},
    pdf = {../../../docs/mohrReehMadsenNature1998InSARGlacierFlowAndDEM.pdf},
    url = {http://dx.doi.org/10.1038/34635},
    
    }
    




18. Eric J. Rignot. Fast Recession of a West Antarctic Glacier. Science, 281(5376):549-551, 1998.

    Abstract:

    Satellite radar interferometry observations of Pine Island Glacier, West Antarctica, reveal that the glacier hinge-line position retreated 1.2 +/- 0.3 kilometers per year between 1992 and 1996, which in turn implies that the ice thinned by 3.5 +/- 0.9 meters per year. The fast recession of Pine Island Glacier, predicted to be a possible trigger for the disintegration of the West Antarctic Ice Sheet, is attributed to enhanced basal melting of the glacier floating tongue by warm ocean waters.

    
    

    @Article{rignotScience1998AntarticGlacier,
    author = {Rignot, Eric J.},
    title = {Fast Recession of a West Antarctic Glacier},
    journal = {Science},
    year = {1998},
    volume = {281},
    number = {5376},
    pages = {549-551},
    abstract = {Satellite radar interferometry observations of Pine Island Glacier, West Antarctica, reveal that the glacier hinge-line position retreated 1.2 +/- 0.3 kilometers per year between 1992 and 1996, which in turn implies that the ice thinned by 3.5 +/- 0.9 meters per year. The fast recession of Pine Island Glacier, predicted to be a possible trigger for the disintegration of the West Antarctic Ice Sheet, is attributed to enhanced basal melting of the glacier floating tongue by warm ocean waters.},
    doi = {10.1126/science.281.5376.549},
    eprint = {http://www.sciencemag.org/content/281/5376/549.full.pdf},
    file = {:rignotScience1998AntarticGlacier.pdf:PDF},
    pdf = {../../../docs/rignotScience1998AntarticGlacier.pdf},
    url = {http://www.sciencemag.org/content/281/5376/549.abstract},
    
    }
    




19. David T. Sandwell and Evelyn J. Price. Phase gradient approach to stacking interferograms. Journal of Geophysical Research: Solid Earth, 103(B12):30183-30204, 1998. Keyword(s): SAR Processing, Interferometry, SAR interferometry, differential SAR interferometry, Inteferogram Stacking, DInSAR, Displacement, Surface Displacement, Deformation Mapping, Deformation Monitoring, Oceanic structures, Space geodetic surveys, Instruments and techniques, Tectonophysics: Dynamics, seismotectonics.

    Abstract:

    The phase gradient approach is used to construct averages and differences of interferograms without phase unwrapping. Our objectives for change detection are to increase fringe clarity and decrease errors due to tropospheric and ionospheric delay by averaging many interferograms. The standard approach requires phase unwrapping, scaling the phase according to the ratio of the perpendicular baseline, and finally forming the average or difference; however, unique phase unwrapping is usually not possible. Since the phase gradient due to topography is proportional to the perpendicular baseline, phase unwrapping is unnecessary prior to averaging or differencing. Phase unwrapping may be needed to interpret the results, but it is delayed until all of the largest topographic signals are removed. We demonstrate the method by averaging and differencing six interferograms having a suite of perpendicular baselines ranging from 18 to 406 m. Cross-spectral analysis of the difference between two Tandem interferograms provides estimates of spatial resolution, which are used to design prestack filters. A wide range of perpendicular baselines provides the best topographic recovery in terms of accuracy and coverage. Outside of mountainous areas the topography has a relative accuracy of better than 2 m. Residual interferograms (single interferogram minus stack) have tilts across the unwrapped phase that are typically 50 mm in both range and azimuth, reflecting both orbit error and atmospheric delay. Smaller-scale waves with amplitudes of 15 mm are interpreted as atmospheric lee waves. A few Global Positioning System (GPS) control points within a frame could increase the precision to 20 mm for a single interferogram; further improvements may be achieved by stacking residual interferograms.

    
    

    @Article{sandwellPriceJGRB1998InterferogramStackingPhaseGradient,
    author = {Sandwell, David T. and Price, Evelyn J.},
    title = {Phase gradient approach to stacking interferograms},
    journal = {Journal of Geophysical Research: Solid Earth},
    year = {1998},
    volume = {103},
    number = {B12},
    pages = {30183-30204},
    issn = {2156-2202},
    abstract = {The phase gradient approach is used to construct averages and differences of interferograms without phase unwrapping. Our objectives for change detection are to increase fringe clarity and decrease errors due to tropospheric and ionospheric delay by averaging many interferograms. The standard approach requires phase unwrapping, scaling the phase according to the ratio of the perpendicular baseline, and finally forming the average or difference; however, unique phase unwrapping is usually not possible. Since the phase gradient due to topography is proportional to the perpendicular baseline, phase unwrapping is unnecessary prior to averaging or differencing. Phase unwrapping may be needed to interpret the results, but it is delayed until all of the largest topographic signals are removed. We demonstrate the method by averaging and differencing six interferograms having a suite of perpendicular baselines ranging from 18 to 406 m. Cross-spectral analysis of the difference between two Tandem interferograms provides estimates of spatial resolution, which are used to design prestack filters. A wide range of perpendicular baselines provides the best topographic recovery in terms of accuracy and coverage. Outside of mountainous areas the topography has a relative accuracy of better than 2 m. Residual interferograms (single interferogram minus stack) have tilts across the unwrapped phase that are typically 50 mm in both range and azimuth, reflecting both orbit error and atmospheric delay. Smaller-scale waves with amplitudes of 15 mm are interpreted as atmospheric lee waves. A few Global Positioning System (GPS) control points within a frame could increase the precision to 20 mm for a single interferogram; further improvements may be achieved by stacking residual interferograms.},
    doi = {10.1029/1998JB900008},
    file = {:sandwellPriceJGRB1998InterferogramStackingPhaseGradient.pdf:PDF},
    keywords = {SAR Processing, Interferometry, SAR interferometry, differential SAR interferometry, Inteferogram Stacking, DInSAR, Displacement, Surface Displacement, Deformation Mapping, Deformation Monitoring, Oceanic structures, Space geodetic surveys, Instruments and techniques, Tectonophysics: Dynamics, seismotectonics},
    pdf = {../../../docs/sandwellPriceJGRB1998InterferogramStackingPhaseGradient.pdf},
    url = {http://dx.doi.org/10.1029/1998JB900008},
    
    }
    




20. Beat Schmid, Paul R Spyak, Stuart F Biggar, Christoph Wehrli, Jörg Sekler, Thomas Ingold, Christian Mätzler, and Niklaus Kämpfer. Evaluation of the applicability of solar and lamp radiometric calibrations of a precision Sun photometer operating between 300 and 1025 nm. Applied Optics, 37(18):3923-3941, 1998.
    

    @Article{Schmid1998,
    author = {Schmid, Beat and Spyak, Paul R and Biggar, Stuart F and Wehrli, Christoph and Sekler, J{\"o}rg and Ingold, Thomas and M{\"a}tzler, Christian and K{\"a}mpfer, Niklaus},
    title = {Evaluation of the applicability of solar and lamp radiometric calibrations of a precision Sun photometer operating between 300 and 1025 nm},
    journal = {Applied Optics},
    year = {1998},
    volume = {37},
    number = {18},
    pages = {3923--3941},
    owner = {ofrey},
    publisher = {Optical Society of America},
    
    }
    




21. Martin Schneebeli and Jerome B. Johnson. A constant-speed penetrometer for high-resolution snow stratigraphy. Annals of Glaciology, 26:107-111, 1998. Keyword(s): snow, snow micro pen, snow stratigraphy.

    Abstract:

    A new constant-speed penetrometer for field and laboratory measurement has been developed. The initially independent work of SFISAR and CRREL has been brought together, and a portable field device is now in an advanced stage of testing. The new penetrometer has high rigidity and a high-resolution large dynamic range force sensor. It uses a much smaller sensing head (5mm) than previous designs and has a constant-speed drive. With this construction, the penetration resistance of very fine layers and the influence of the bonding strength between snow grains can be more accurately determined than is possible with the rammsonde or Pandalp. Artificial foam layers as thin as 2 mm and thin layers in snow have been detected by the penetrometer. Thin snow layers detected from penetration-resistance profiles have been correlated to fine layering as determined from plane-section microphotographs of samples taken adjacent to the profile. The instrument's measurements are highly repeatable and the lack of subjective decisions when operating the penetrometer makes the penetration resistance a quantitative measure of snow stratigraphy.

    
    

    @Article{schneebeliJohnson1998SnowMicroPen,
    author = {Schneebeli, Martin and Johnson, Jerome B.},
    journal = {Annals of Glaciology},
    title = {A constant-speed penetrometer for high-resolution snow stratigraphy},
    year = {1998},
    pages = {107-111},
    volume = {26},
    abstract = {A new constant-speed penetrometer for field and laboratory measurement has been developed. The initially independent work of SFISAR and CRREL has been brought together, and a portable field device is now in an advanced stage of testing. The new penetrometer has high rigidity and a high-resolution large dynamic range force sensor. It uses a much smaller sensing head (5mm) than previous designs and has a constant-speed drive. With this construction, the penetration resistance of very fine layers and the influence of the bonding strength between snow grains can be more accurately determined than is possible with the rammsonde or Pandalp. Artificial foam layers as thin as 2 mm and thin layers in snow have been detected by the penetrometer. Thin snow layers detected from penetration-resistance profiles have been correlated to fine layering as determined from plane-section microphotographs of samples taken adjacent to the profile. The instrument's measurements are highly repeatable and the lack of subjective decisions when operating the penetrometer makes the penetration resistance a quantitative measure of snow stratigraphy.},
    doi = {10.3189/1998AoG26-1-107-111},
    file = {:schneebeliJohnson1998SnowMicroPen.pdf:PDF},
    keywords = {snow, snow micro pen, snow stratigraphy},
    publisher = {Cambridge University Press},
    
    }
    




22. Tazio Strozzi and Christian Matzler. Backscattering measurements of alpine snowcovers at 5.3 and 35 GHz. IEEE Transactions on Geoscience and Remote Sensing, 36(3):838-848, May 1998. Keyword(s): backscatter, hydrological techniques, radar cross-sections, radar polarimetry, remote sensing by radar, snow, 35 GHz, 5.3 GHz, AD 1993, AD 1994, AD 1995, AD 1996, Austria, Austrian Alp, C-band, EHF, Ka-band, SHF, Switzerland, hydrology, measurement technique, network-analyzer based scatterometer, radar backscatter, radar polarimetry, radar remote sensing, radar scattering, refrozen crust thickness, snow cover, snowcover, volumetric liquid water content, Backscatter, Frequency, Instruments, Millimeter wave measurements, Performance evaluation, Physics, Polarization, Radar measurements, Snow, Testing.

    Abstract:

    This paper describes two network-analyzer (NA)-based scatterometers at 5.3 (C-band) and 35 GHz (Ka-band) as well as snowcover measurements made in the Swiss and Austrian Alps between December 1993 and January 1996. First, the setup and the mode of operation of the scatterometers are discussed. Both instruments measure the backscattering coefficients gamma at hh, vv, vh, and vh polarizations and for incidence angles ranging from 0 to 70deg. The accuracy of gamma is generally better than +/-1.8 dB, and the scatterometers are well suited for signature studies of natural surfaces. During the two years, the authors performed many backscattering measurements of natural, strongly layered snowcovers and the authors investigated relationships between gamma and physical parameters of the snowcover. All measurements were collected in a signature catalogue. They report on results at 40deg incidence angle. They found that the combined use of active sensors at 5.3 and 35 GHz allows the discrimination of various snowcover situations, if multitemporal information is available. In addition, they observed a relationship of gamma at 5.3 GHz with the integrated column height of liquid water and dependencies of gamma at 35 GHz on the height of the dry snow, on the volumetric liquid water content at the snow surface, and on the thickness of the refrozen crust at the snow surface

    
    

    @Article{strozziMatzlerTGRS1998Snow,
    author = {Tazio Strozzi and Christian Matzler},
    title = {Backscattering measurements of alpine snowcovers at 5.3 and 35 {GHz}},
    journal = {IEEE Transactions on Geoscience and Remote Sensing},
    year = {1998},
    volume = {36},
    number = {3},
    pages = {838-848},
    month = may,
    issn = {0196-2892},
    abstract = {This paper describes two network-analyzer (NA)-based scatterometers at 5.3 (C-band) and 35 GHz (Ka-band) as well as snowcover measurements made in the Swiss and Austrian Alps between December 1993 and January 1996. First, the setup and the mode of operation of the scatterometers are discussed. Both instruments measure the backscattering coefficients gamma at hh, vv, vh, and vh polarizations and for incidence angles ranging from 0 to 70deg. The accuracy of gamma is generally better than +/-1.8 dB, and the scatterometers are well suited for signature studies of natural surfaces. During the two years, the authors performed many backscattering measurements of natural, strongly layered snowcovers and the authors investigated relationships between gamma and physical parameters of the snowcover. All measurements were collected in a signature catalogue. They report on results at 40deg incidence angle. They found that the combined use of active sensors at 5.3 and 35 GHz allows the discrimination of various snowcover situations, if multitemporal information is available. In addition, they observed a relationship of gamma at 5.3 GHz with the integrated column height of liquid water and dependencies of gamma at 35 GHz on the height of the dry snow, on the volumetric liquid water content at the snow surface, and on the thickness of the refrozen crust at the snow surface},
    doi = {10.1109/36.673677},
    file = {:strozziMatzlerTGRS1998Snow.pdf:PDF},
    keywords = {backscatter;hydrological techniques;radar cross-sections;radar polarimetry;remote sensing by radar;snow;35 GHz;5.3 GHz;AD 1993;AD 1994;AD 1995;AD 1996;Austria;Austrian Alp;C-band;EHF;Ka-band;SHF;Switzerland;hydrology;measurement technique;network-analyzer based scatterometer;radar backscatter;radar polarimetry;radar remote sensing;radar scattering;refrozen crust thickness;snow cover;snowcover;volumetric liquid water content;Backscatter;Frequency;Instruments;Millimeter wave measurements;Performance evaluation;Physics;Polarization;Radar measurements;Snow;Testing},
    owner = {ofrey},
    pdf = {../../../docs/strozziMatzlerTGRS1998Snow.pdf},
    
    }
    




23. Lars M. H. Ulander and Per-Olov Frölind. Ultra-Wideband SAR Interferometry. IEEE Transactions on Geoscience and Remote Sensing, 36(5):1540-1550, September 1998. Keyword(s): SAR Processing, Interferometry, DEM Generation, Fourier-Hankel Inversion, Hankel Transform, Abel Transform, Ultra-Wideband SAR, VHF SAR, CARABAS, Airborne SAR.

    Abstract:

    We introduce ultra-wideband synthetic aperture radar (SAR) interferometry as a new technique for topographic height retrieval. It is based on using a SAR system with large relative bandwidth that acquires data along two parallel tracks with a separation of the same order of magnitude as the flight altitude. The complex SAR image data are resampled onto a common reference surface, filtered, and followed by a Hermitian multiplication. The resulting interferogram is shown to have a finite depth-of-focus (DOF) in terms of phase coherence. The achieved height precision is controlled by the ambiguity height, which is shown to scale to the DOF as the relative bandwidth. This means that only one fringe is within the DOF as the resolution approaches the fundamental wavelength limit; i.e., the phase is unambiguously related to topographic height. The topography may thus be determined by changing the reference surface and retrieving the height at each step. The technique is successfully demonstrated to generate fringes based on VHF-band data acquired by the CARABAS airborne SAR system. Temporal decorrelation is not a problem due to the long wavelengths nor is the effect of tropospheric delay on the retrieved height.

    
    

    @Article{ulanderfroelind98:Interfero,
    author = {Lars M. H. Ulander and Per-Olov Fr{\"o}lind},
    title = {{Ultra-Wideband SAR Interferometry}},
    journal = {IEEE Transactions on Geoscience and Remote Sensing},
    year = {1998},
    volume = {36},
    number = {5},
    pages = {1540-1550},
    month = sep,
    abstract = {We introduce ultra-wideband synthetic aperture radar (SAR) interferometry as a new technique for topographic height retrieval. It is based on using a SAR system with large relative bandwidth that acquires data along two parallel tracks with a separation of the same order of magnitude as the flight altitude. The complex SAR image data are resampled onto a common reference surface, filtered, and followed by a Hermitian multiplication. The resulting interferogram is shown to have a finite depth-of-focus (DOF) in terms of phase coherence. The achieved height precision is controlled by the ambiguity height, which is shown to scale to the DOF as the relative bandwidth. This means that only one fringe is within the DOF as the resolution approaches the fundamental wavelength limit; i.e., the phase is unambiguously related to topographic height. The topography may thus be determined by changing the reference surface and retrieving the height at each step. The technique is successfully demonstrated to generate fringes based on VHF-band data acquired by the CARABAS airborne SAR system. Temporal decorrelation is not a problem due to the long wavelengths nor is the effect of tropospheric delay on the retrieved height.},
    file = {:ulanderfroelind98.pdf:PDF},
    keywords = {SAR Processing, Interferometry, DEM Generation, Fourier-Hankel Inversion, Hankel Transform, Abel Transform, Ultra-Wideband SAR, VHF SAR, CARABAS, Airborne SAR},
    pdf = {../../../docs/ulanderfroelind98.pdf},
    url = {http://ieeexplore.ieee.org/iel4/36/15531/00718858.pdf},
    
    }
    




24. Andreas Wiesmann, Christian Matzler, and Thomas Weise. Radiometric and structural measurements of snow samples. Radio Science, 33(2):273-289, 1998.

    Abstract:

    The interaction of microwaves with the natural snow cover strongly depends on the complex structure of the snowpack. In order to quantify this dependency, dedicated experiments were performed with homogeneous slabs of dry, natural snow samples measured over a frequency range from 11 to 94 GHz. A new method introduced by M{\"a}tzler and Wegm{\"u}ller [1995] and Weise [1996a] for determining the scattering and absorption behavior of test samples was applied and further developed by application of a multiple scattering model. Homogeneous samples of dry snow were (1) investigated using a set of portable, linearly polarized Dicke radiometers at frequencies of 11, 21, 35, 48 and 94 GHz, (2) characterized by temperature, grain size and shape, density and permittivity, and (3) structurally analyzed by digitized snow sections in order to obtain statistical information of the snow structure i.e. the autocorrelation function. During the winters 1994/1995 and 1995/1996 additional measurements of snow samples were made to extend the variability of the investigated snow types. Up to now, 20 samples, representing alpine snow in winter (that is, without melt metamorphism) have been collected during three winter campaigns. Here, we present the method and the radiative transfer model and show how it can be inverted to obtain scattering and absorption coefficients. A first assessment of the snow sample data is also presented. The results show good agreement between the measured and the theoretical absorption coefficient. The scattering coefficient turns out to be a strong function of frequency and correlation length as expected from Rayleigh scattering. However, distinct differences can be noted.

    
    

    @Article{wiesmannMatzlerWeiseRadioScience1998RadiometricStructuralMeasurementOfSnowSamples,
    author = {Wiesmann, Andreas and Matzler, Christian and Weise, Thomas},
    title = {Radiometric and structural measurements of snow samples},
    journal = {Radio Science},
    year = {1998},
    volume = {33},
    number = {2},
    pages = {273--289},
    abstract = {The interaction of microwaves with the natural snow cover strongly depends on the complex structure of the snowpack. In order to quantify this dependency, dedicated experiments were performed with homogeneous slabs of dry, natural snow samples measured over a frequency range from 11 to 94 GHz. A new method introduced by M{\"a}tzler and Wegm{\"u}ller [1995] and Weise [1996a] for determining the scattering and absorption behavior of test samples was applied and further developed by application of a multiple scattering model. Homogeneous samples of dry snow were (1) investigated using a set of portable, linearly polarized Dicke radiometers at frequencies of 11, 21, 35, 48 and 94 GHz, (2) characterized by temperature, grain size and shape, density and permittivity, and (3) structurally analyzed by digitized snow sections in order to obtain statistical information of the snow structure i.e. the autocorrelation function. During the winters 1994/1995 and 1995/1996 additional measurements of snow samples were made to extend the variability of the investigated snow types. Up to now, 20 samples, representing alpine snow in winter (that is, without melt metamorphism) have been collected during three winter campaigns. Here, we present the method and the radiative transfer model and show how it can be inverted to obtain scattering and absorption coefficients. A first assessment of the snow sample data is also presented. The results show good agreement between the measured and the theoretical absorption coefficient. The scattering coefficient turns out to be a strong function of frequency and correlation length as expected from Rayleigh scattering. However, distinct differences can be noted.},
    file = {:wiesmannMatzlerWeiseRadioScience1998RadiometricStructuralMeasurementOfSnowSamples.pdf:PDF},
    owner = {ofrey},
    pdf = {../../../docs/wiesmannMatzlerWeiseRadioScience1998RadiometricStructuralMeasurementOfSnowSamples.pdf},
    publisher = {Wiley Online Library},
    
    }
    




25. Simon Williams, Yehuda Bock, and Peng Fang. Integrated satellite interferometry: Tropospheric noise, GPS estimates and implications for interferometric synthetic aperture radar products. Journal of Geophysical Research: Solid Earth, 103(B11):27051-27067, 1998. Keyword(s): SAR Processing, Interferometry, SAR interferometry, differential SAR interferometry, DInSAR, Displacement, Surface Displacement, Atmosphere, APS, Geodesy and Gravity, Instruments and techniques, GPS, GNSS.

    Abstract:

    Interferometric synthetic aperture radar (INSAR), like other astronomic and space geodetic techniques, is limited by the spatially and temporally variable delay of electromagnetic waves propagating through the neutral atmosphere. Statistical analysis of these variations, from a wide variety of instruments, reveals a power law dependence on frequency that is characteristic of elementary (Kolmogorov) turbulence. A statistical model for a major component of the delay fluctuations, the ''wet'' component, has previously been developed by Treuhaft and Lanyi [1987] for very long baseline interferometry. A continuous Global Positioning System (GPS) network is now in place in southern California that allows estimation of, along with geodetic parameters, the total delay due to the atmosphere above each site on a subhourly basis. These measurements are shown to conform to the Treuhaft and Lanyi (TL) statistical model both temporally and spatially. The TL statistical model is applied to the problem of INSAR and used to produce the covariance between two points separated in time and/or space. The error, due to the atmospheric variations, for SAR products such as topography and surface deformation is calculated via propagation of errors. There are two methods commonly cited to reduce the effect of atmospheric distortion in products from SAR interferometry, stacking and calibration. Stacking involves averaging independent interferograms to reduce the noise. Calibration involves removing part (or all) of the delay using data from an independent source such as total zenith delay estimates from continuous GPS networks. Despite the relatively poor spatial density of surface measurements, calibration can be used to reduce noise if the measurements are sufficiently accurate. Reduction in tropospheric noise increases with increasing number of measurement points and increasing accuracy up to a maximum of sqrt(N), where N is the number of points. Stacking and calibration are shown to be complementary and can be used simultaneously to reduce the noise to below that achievable by either method alone.

    
    

    @Article{williamsBockFangJGRBInSARandGPSTroposphere,
    author = {Williams, Simon and Bock, Yehuda and Fang, Peng},
    journal = {Journal of Geophysical Research: Solid Earth},
    title = {Integrated satellite interferometry: Tropospheric noise, {GPS} estimates and implications for interferometric synthetic aperture radar products},
    year = {1998},
    issn = {2156-2202},
    number = {B11},
    pages = {27051--27067},
    volume = {103},
    abstract = {Interferometric synthetic aperture radar (INSAR), like other astronomic and space geodetic techniques, is limited by the spatially and temporally variable delay of electromagnetic waves propagating through the neutral atmosphere. Statistical analysis of these variations, from a wide variety of instruments, reveals a power law dependence on frequency that is characteristic of elementary (Kolmogorov) turbulence. A statistical model for a major component of the delay fluctuations, the ''wet'' component, has previously been developed by Treuhaft and Lanyi [1987] for very long baseline interferometry. A continuous Global Positioning System (GPS) network is now in place in southern California that allows estimation of, along with geodetic parameters, the total delay due to the atmosphere above each site on a subhourly basis. These measurements are shown to conform to the Treuhaft and Lanyi (TL) statistical model both temporally and spatially. The TL statistical model is applied to the problem of INSAR and used to produce the covariance between two points separated in time and/or space. The error, due to the atmospheric variations, for SAR products such as topography and surface deformation is calculated via propagation of errors. There are two methods commonly cited to reduce the effect of atmospheric distortion in products from SAR interferometry, stacking and calibration. Stacking involves averaging independent interferograms to reduce the noise. Calibration involves removing part (or all) of the delay using data from an independent source such as total zenith delay estimates from continuous GPS networks. Despite the relatively poor spatial density of surface measurements, calibration can be used to reduce noise if the measurements are sufficiently accurate. Reduction in tropospheric noise increases with increasing number of measurement points and increasing accuracy up to a maximum of sqrt(N), where N is the number of points. Stacking and calibration are shown to be complementary and can be used simultaneously to reduce the noise to below that achievable by either method alone.},
    doi = {10.1029/98JB02794},
    file = {:williamsBockFangJGRBInSARandGPSTroposphere.pdf:PDF},
    keywords = {SAR Processing, Interferometry, SAR interferometry, differential SAR interferometry, DInSAR, Displacement, Surface Displacement, Atmosphere, APS, Geodesy and Gravity, Instruments and techniques, GPS, GNSS},
    pdf = {../../../docs/williamsBockFangJGRBInSARandGPSTroposphere.pdf},
    url = {http://dx.doi.org/10.1029/98JB02794},
    
    }
    

Conference articles

1. Stefan Buckreuss and Ralf Horn. E-SAR P-band SAR subsystem design and RF-interference suppression. In Geoscience and Remote Sensing Symposium Proceedings, 1998. IGARSS '98. 1998 IEEE International, volume 1, pages 466-468, 1998. Keyword(s): SAR Processing, airborne radar, interference suppression, microstrip antenna arrays, radar interference, radar polarimetry, synthetic aperture radar, 450 MHz, E-SAR P-band SAR subsystem design, Germany, Institut fur Hochfrequenztechnik, P-Band, P-band radar front-end, RFI Suppression, RF-interference suppression, Weilheim, carrier frequency, experimental airborne synthetic aperture radar, microstrip patch array antenna, polarimetric radar, signal bandwidth.

   Abstract:

   Since the beginning of 1994 the Institut f{\"u}r Hochfrequenztechnik of the German Aerospace Center (DLR) has been operating an experimental airborne SAR E-SAR with a P-band radar front-end. The microstrip patch array antenna allows a signal bandwidth of slightly more than 10% of the 450 MHz carrier frequency. The radar is polarimetric on a pulse-to-pulse basis.

   
   

   @InProceedings{buckreussHorn98:RFI,
   author = {Buckreuss, Stefan and Horn, Ralf},
   booktitle = {Geoscience and Remote Sensing Symposium Proceedings, 1998. IGARSS '98. 1998 IEEE International},
   title = {E-SAR P-band SAR subsystem design and RF-interference suppression},
   year = {1998},
   pages = {466--468},
   volume = {1},
   abstract = {Since the beginning of 1994 the Institut f{\"u}r Hochfrequenztechnik of the German Aerospace Center (DLR) has been operating an experimental airborne SAR E-SAR with a P-band radar front-end. The microstrip patch array antenna allows a signal bandwidth of slightly more than 10% of the 450 MHz carrier frequency. The radar is polarimetric on a pulse-to-pulse basis.},
   keywords = {SAR Processing, airborne radar, interference suppression, microstrip antenna arrays, radar interference, radar polarimetry, synthetic aperture radar, 450 MHz, E-SAR P-band SAR subsystem design, Germany, Institut fur Hochfrequenztechnik, P-Band, P-band radar front-end, RFI Suppression, RF-interference suppression, Weilheim, carrier frequency, experimental airborne synthetic aperture radar, microstrip patch array antenna, polarimetric radar, signal bandwidth},
   owner = {ofrey},
   pdf = {../../../docs/buckreussHorn98.pdf},
   
   }
   




2. N. Doren and D.E. Wahl. Implementation of SAR interferometric map generation using parallel processors. In IGARSS '98. Sensing and Managing the Environment. 1998 IEEE International Geoscience and Remote Sensing. Symposium Proceedings. (Cat. No.98CH36174), volume 5, pages 2640-2642 vol.5, July 1998. Keyword(s): Pixel, Layout, Geometry, Laboratories, Synthetic aperture radar interferometry, Phase estimation, Parallel processing, Reflectivity, Azimuth, Postal services.

   Abstract:

   Interferometric fringe maps are generated by accurately registering a pair of complex SAR images of the same scene imaged from two very similar geometries, and calculating the phase difference between the two images by averaging over a neighborhood of pixels at each spatial location. The phase difference (fringe) map resulting from this IFSAR operation is then unwrapped and used to calculate the height estimate of the imaged terrain. Although the method used to calculate interferometric fringe maps is well known, it is generally executed in a post-processing mode well after the image pairs have been collected. In that mode of operation, there is little concern about algorithm speed and the method is normally implemented on a single processor machine. This paper describes how the interferometric map generation is implemented on a distributed-memory parallel processing machine. This particular implementation is designed to operate on a 16 node Power-PC platform and to generate interferometric maps in near real-time. The implementation is able to accommodate large translational offsets, along with a slight amount of rotation which may exist between the interferometric pair of images. If the number of pixels in the IFSAR image is large enough, the implementation accomplishes nearly linear speed-up times with the addition of processors.

   
   

   @InProceedings{Doren1998,
   author = {Doren, N. and Wahl, D.E.},
   booktitle = {IGARSS '98. Sensing and Managing the Environment. 1998 IEEE International Geoscience and Remote Sensing. Symposium Proceedings. (Cat. No.98CH36174)},
   title = {Implementation of SAR interferometric map generation using parallel processors},
   year = {1998},
   month = {July},
   pages = {2640-2642 vol.5},
   volume = {5},
   abstract = {Interferometric fringe maps are generated by accurately registering a pair of complex SAR images of the same scene imaged from two very similar geometries, and calculating the phase difference between the two images by averaging over a neighborhood of pixels at each spatial location. The phase difference (fringe) map resulting from this IFSAR operation is then unwrapped and used to calculate the height estimate of the imaged terrain. Although the method used to calculate interferometric fringe maps is well known, it is generally executed in a post-processing mode well after the image pairs have been collected. In that mode of operation, there is little concern about algorithm speed and the method is normally implemented on a single processor machine. This paper describes how the interferometric map generation is implemented on a distributed-memory parallel processing machine. This particular implementation is designed to operate on a 16 node Power-PC platform and to generate interferometric maps in near real-time. The implementation is able to accommodate large translational offsets, along with a slight amount of rotation which may exist between the interferometric pair of images. If the number of pixels in the IFSAR image is large enough, the implementation accomplishes nearly linear speed-up times with the addition of processors.},
   doi = {10.1109/IGARSS.1998.702305},
   keywords = {Pixel;Layout;Geometry;Laboratories;Synthetic aperture radar interferometry;Phase estimation;Parallel processing;Reflectivity;Azimuth;Postal services},
   owner = {ofrey},
   
   }
   




3. Francesco Holecz, Paolo Pasquali, João Moreira, and Daniel Nüesch. Rigorous radiometric calibration of airborne AeS-1 InSAR data. In IGARSS '98, Geoscience and Remote Sensing Symposium, volume 5, pages 2442-2444, 1998. Keyword(s): SAR Processing, Radiometry, Radiometric Calibration, Airborne SAR, Topography, Interferometry, calibration, geophysical techniques, remote sensing by radar, synthetic aperture radar, 9.6 GHz, AeS-1, InSAR, X-band, airborne radar, elevation data, geophysical measurement technique, interferometric SAR, land surface, radar remote sensing, radiometric calibration, terrain mapping, topographic data.

   Abstract:

   The processing of synthetic aperture radar images usually does not

   
   

   @InProceedings{HoleczPasqualiMoreiraNuesch98:RadiometricCalibrationAes1Data,
   author = {Holecz, Francesco and Pasquali, Paolo and Moreira, Jo{\~a}o and N{\"u}esch, Daniel},
   booktitle = {IGARSS '98, Geoscience and Remote Sensing Symposium},
   title = {{Rigorous radiometric calibration of airborne AeS-1 InSAR data}},
   year = {1998},
   pages = {2442--2444},
   volume = {5},
   abstract = {The processing of synthetic aperture radar images usually does not},
   keywords = {SAR Processing, Radiometry, Radiometric Calibration, Airborne SAR, Topography, Interferometry, calibration, geophysical techniques, remote sensing by radar, synthetic aperture radar, 9.6 GHz, AeS-1, InSAR, X-band, airborne radar, elevation data, geophysical measurement technique, interferometric SAR, land surface, radar remote sensing, radiometric calibration, terrain mapping, topographic data},
   owner = {ofrey},
   pdf = {../../../docs/HoleczPasqualiMoreiraNuesch98.pdf},
   url = {http://ieeexplore.ieee.org/iel4/5660/15200/00702240.pdf},
   
   }
   




4. Charles V. Jakowatz, Daniel E. Wahl, and Paul H. Eichel. Refocus of constant-velocity moving targets in synthetic aperture radar imagery. In Edmund G. Zelnio, editor, , volume 3370, pages 85-95, 1998. SPIE. Keyword(s): SAR Processing, Moving Target Indication, MTI.
   

   @Conference{jakowatzWahlEichelRefocusMovingTargets,
   author = {Charles V. Jakowatz and Daniel E. Wahl and Paul H. Eichel},
   title = {Refocus of constant-velocity moving targets in synthetic aperture radar imagery},
   year = {1998},
   editor = {Edmund G. Zelnio},
   volume = {3370},
   number = {1},
   pages = {85-95},
   publisher = {SPIE},
   doi = {10.1117/12.321814},
   file = {:jakowatzWahlEichelRefocusMovingTargets.pdf:PDF},
   journal = {Algorithms for Synthetic Aperture Radar Imagery V},
   keywords = {SAR Processing, Moving Target Indication, MTI},
   location = {Orlando, FL, USA},
   owner = {ofrey},
   pdf = {../../../docs/jakowatzWahlEichelRefocusMovingTargets.pdf},
   url = {http://link.aip.org/link/?PSI/3370/85/1},
   
   }
   




5. Bruno Juhel, Yannick Chevalier, Marc Le Goff, Emmanuel Legros, and Georges Vezzosi. Experimental Ultra Wide Band SAR Images of Canonical Targets. In IGARSS '98, International Geoscience and Remote Sensing Symposium, volume 2, pages 1153-1155, 1998. Keyword(s): SAR Processing, Back-Projection, Time-Domain Back-Projection, Ultra-Wideband SAR.

   Abstract:

   This paper describes one technique for ultra wide band (UWB) time domain radar signal processing. Usually a radar is a narrow band system, but in this case transmitted signals are nanosecond short pulses without carrier which have a spectral content from 100 MHz to 1 GHz. Time domain backprojection is used to focus SAR images. The algorithm is tested with experimental data measured with an UWB prototype radar. The configuration of this radar is described and some UWB SAR images of canonical targets are presented

   
   

   @InProceedings{JuhelEtAl98:Backproj,
   Title = {{Experimental Ultra Wide Band SAR Images of Canonical Targets}},
   Author = {Bruno Juhel and Yannick Chevalier and Marc Le Goff and Emmanuel Legros and Georges Vezzosi},
   Booktitle = {IGARSS '98, International Geoscience and Remote Sensing Symposium},
   Pages = {1153-1155},
   Volume = {2},
   Year = {1998},
   Abstract = {This paper describes one technique for ultra wide band (UWB) time domain radar signal processing. Usually a radar is a narrow band system, but in this case transmitted signals are nanosecond short pulses without carrier which have a spectral content from 100 MHz to 1 GHz. Time domain backprojection is used to focus SAR images. The algorithm is tested with experimental data measured with an UWB prototype radar. The configuration of this radar is described and some UWB SAR images of canonical targets are presented},
   Keywords = {SAR Processing, Back-Projection, Time-Domain Back-Projection, Ultra-Wideband SAR},
   Pdf = {../../../docs/juhelEtAl98.pdf} 
   }
   




6. Bruno Juhel, Georges Vezzosi, and Marc Le Goff. Radio Frequency Interferences Suppression for Noisy Ultra Wide Band SAR Measurements. In Ultra-Wideband Short-Pulse Electromagnetics 4, 1998, pages 387-393, June 1998. Keyword(s): SAR Processing, Back-Projection, Ultra-Wideband SAR, RFI Suppression.

   Abstract:

   A back projection algorithm dedicated to Ultra Wide Band (UWB) signals for synthetic aperture radar (SAR) imaging is described. The time domain aspect is all the more important that the transient nature of UWB signal supplies a vast amount of information on the electromagnetic scattering mechanisms. But, during UWB measurements, radio frequency interferences (RFI) can appear and obscure target detection. We have described how RFI can be an important noise source in UWB system and how they can be suppressed. The Least Mean Square (LMS) method for extracting RFI give good results, which are quantified with simulated data. Next, we would like to improve our sinusoidal model of the RFI to include a more complete description of the RFI signal and to apply the LMS algorithm to measured data

   
   

   @InProceedings{JuhelVezzosiLeGoff98:Backproj,
   Title = {{Radio Frequency Interferences Suppression for Noisy Ultra Wide Band SAR Measurements}},
   Author = {Bruno Juhel and Georges Vezzosi and Marc Le Goff},
   Booktitle = {Ultra-Wideband Short-Pulse Electromagnetics 4, 1998},
   Month = Jun,
   Pages = {387-393},
   Url = {http://ieeexplore.ieee.org/iel5/6640/17710/00818972.pdf},
   Year = {1998},
   Abstract = {A back projection algorithm dedicated to Ultra Wide Band (UWB) signals for synthetic aperture radar (SAR) imaging is described. The time domain aspect is all the more important that the transient nature of UWB signal supplies a vast amount of information on the electromagnetic scattering mechanisms. But, during UWB measurements, radio frequency interferences (RFI) can appear and obscure target detection. We have described how RFI can be an important noise source in UWB system and how they can be suppressed. The Least Mean Square (LMS) method for extracting RFI give good results, which are quantified with simulated data. Next, we would like to improve our sinusoidal model of the RFI to include a more complete description of the RFI signal and to apply the LMS algorithm to measured data},
   Keywords = {SAR Processing, Back-Projection, Ultra-Wideband SAR, RFI Suppression},
   Pdf = {../../../docs/JuhelVezzosiLeGoff98.pdf} 
   }
   




7. Kenneth Knaell. Progress in three-dimensional SAR from curvilinear apertures. In William J. Miceli, editor, , volume 3462, pages 110-121, 1998. SPIE. Keyword(s): SAR Processing, Non-Linear Flight Path, SAR Tomography, Curvilinear SAR.
   

   @Conference{knaell:110,
   Title = {Progress in three-dimensional SAR from curvilinear apertures},
   Author = {Kenneth Knaell},
   Editor = {William J. Miceli},
   Doi = {10.1117/12.326738},
   Location = {San Diego, CA, USA},
   Number = {1},
   Pages = {110-121},
   Publisher = {SPIE},
   Url = {http://link.aip.org/link/?PSI/3462/110/1},
   Volume = {3462},
   Year = {1998},
   Journal = {Radar Processing, Technology, and Applications III},
   Keywords = {SAR Processing, Non-Linear Flight Path, SAR Tomography, Curvilinear SAR} 
   }
   




8. Riccardo Lanari, Scott Hensley, and Paul Rosen. Modified SPECAN algorithm for ScanSAR data processing. In IEEE International Geoscience and Remote Sensing Symposium, volume 2, pages 636-638, July 1998. Keyword(s): SAR Processing, Modified SPECAN, SPECAN, Spectral Analysis, geophysical signal processing, geophysical techniques, radar imaging, remote sensing by radar, spaceborne radar, synthetic aperture radarSAR, ScanSAR, ScanSAR image, chirp z-transform, chirp-z, geophysical measurement technique, land surface, modified SPECAN algorithm, phase-preserving algorithm, radar remote sensing, range-dependent correction factor, synthetic aperture radar, terrain mapping.

   Abstract:

   The authors present a new phase-preserving algorithm for ScanSAR data processing that extends the SPECAN procedure. The proposed technique allows one to avoid the range dependent scaling of the azimuth pixel dimension, obtained by applying the standard SPECAN approach; this result is achieved by replacing the standard Fourier transform included in the SPECAN algorithm with a chirp z-transform, whose kernel includes a range-dependent correction factor. ScanSAR images generated via the proposed procedure have a constant azimuth pixel spacing whose dimension can be selected according to the application requirements

   
   

   @InProceedings{lanariHensleyRosen1998Short:ModifiedSPECAN,
   author = {Lanari, Riccardo and Hensley, Scott and Rosen, Paul},
   booktitle = {IEEE International Geoscience and Remote Sensing Symposium},
   title = {Modified SPECAN algorithm for ScanSAR data processing},
   year = {1998},
   month = jul,
   pages = {636-638},
   volume = {2},
   abstract = {The authors present a new phase-preserving algorithm for ScanSAR data processing that extends the SPECAN procedure. The proposed technique allows one to avoid the range dependent scaling of the azimuth pixel dimension, obtained by applying the standard SPECAN approach; this result is achieved by replacing the standard Fourier transform included in the SPECAN algorithm with a chirp z-transform, whose kernel includes a range-dependent correction factor. ScanSAR images generated via the proposed procedure have a constant azimuth pixel spacing whose dimension can be selected according to the application requirements},
   doi = {10.1109/IGARSS.1998.699535},
   keywords = {SAR Processing, Modified SPECAN, SPECAN, Spectral Analysis, geophysical signal processing, geophysical techniques, radar imaging, remote sensing by radar, spaceborne radar, synthetic aperture radarSAR, ScanSAR, ScanSAR image, chirp z-transform, chirp-z, geophysical measurement technique, land surface, modified SPECAN algorithm, phase-preserving algorithm, radar remote sensing, range-dependent correction factor, synthetic aperture radar, terrain mapping},
   owner = {ofrey},
   pdf = {../../../docs/lanariHensleyRosen1998Short.pdf},
   url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=699535&isnumber=15176?tag=1},
   
   }
   




9. Li Liwei, Asif Raza, and Mao Shiyi. Improvement of rank one phase estimation (ROPE) autofocusing technique. In Signal Processing Proceedings, 1998. ICSP '98. 1998 Fourth International Conference on, volume 2, pages 1461-1464, October 1998.
   

   @InProceedings{Liwei1998,
   Title = {Improvement of rank one phase estimation (ROPE) autofocusing technique},
   Author = {Li Liwei and Asif Raza and Mao Shiyi},
   Booktitle = {Signal Processing Proceedings, 1998. ICSP '98. 1998 Fourth International Conference on},
   Doi = {10.1109/ICOSP.1998.770896},
   Month = oct,
   Pages = {1461--1464},
   Volume = {2},
   Year = {1998},
   Owner = {ofrey} 
   }
   




10. F. Lombardini, H.D. Griffiths, and F. Gini. A ML multichannel ATI-SAR technique for measuring ocean surface velocities. In OCEANS '98 Conference Proceedings, volume 2, pages 778-782, September 1998.
    

    @InProceedings{Lombardini1998,
    Title = {A ML multichannel ATI-SAR technique for measuring ocean surface velocities},
    Author = {Lombardini, F. and Griffiths, H.D. and Gini, F.},
    Booktitle = {OCEANS '98 Conference Proceedings},
    Doi = {10.1109/OCEANS.1998.724344},
    Month = sep,
    Pages = {778--782},
    Volume = {2},
    Year = {1998},
    Owner = {ofrey} 
    }
    




11. F. Lombardini and P. Lombardo. A ML thinned array SAR interferometric sensor for high accuracy absolute phase retrieval. In Radar Conference, 1998. RADARCON 98. Proceedings of the 1998 IEEE, pages 263-268, May 1998.
    

    @InProceedings{Lombardini1998a,
    Title = {A {ML} thinned array {SAR} interferometric sensor for high accuracy absolute phase retrieval},
    Author = {Lombardini, F. and Lombardo, P.},
    Booktitle = {Radar Conference, 1998. RADARCON 98. Proceedings of the 1998 IEEE},
    Doi = {10.1109/NRC.1998.678012},
    Month = may,
    Pages = {263--268},
    Year = {1998},
    Owner = {ofrey} 
    }
    




12. Richard T. Lord and Michael R. Inggs. Approaches to RF interference suppression for VHF/UHF synthetic aperture radar. In Communications and Signal Processing, 1998. COMSIG '98. Proceedings of the 1998 South African Symposium on, pages 95-100, 1998. Keyword(s): SAR Processing, adaptive filters, adaptive signal processing, interference suppression, least mean squares methods, radar imaging, radar interference, synthetic aperture radar, LMS adaptive filter, P-Band, RF interference suppression, RFI Suppression, SAR imagery, VHF/UHF SAR applications, VHF/UHF synthetic aperture radar, coherent subtraction algorithms, filter approaches, image quality, interference power, least-mean-squared filter, radio frequency interference, receiver noise, spectral estimation.

    Abstract:

    An increasing amount of interest has developed in VHF/UHF SAR applications. Unfortunately the VHF-UHF portion of the spectrum is already in heavy use by other services, such as television and mobile communications. Even in remote locations the interference power often exceeds receiver noise by many dB, becoming the limiting factor on system sensitivity and severely degrading the image quality. This paper addresses the problem of radio frequency (RF) interference and its impact on SAR imagery. Several RF interference suppression methods are described and discussed. These include spectral estimation and coherent subtraction algorithms, as well as various filter approaches. The least-mean-squared (LMS) adaptive filter is described in detail, and its effectiveness in suppressing RF interference is demonstrated on simulated data and on real P-band data.

    
    

    @InProceedings{lordInggs98:RFI,
    Title = {Approaches to RF interference suppression for VHF/UHF synthetic aperture radar},
    Author = {Lord, Richard T. and Inggs, Michael R.},
    Booktitle = {Communications and Signal Processing, 1998. COMSIG '98. Proceedings of the 1998 South African Symposium on},
    Pages = {95--100},
    Url = {http://ieeexplore.ieee.org/iel4/5945/15887/00736929.pdf},
    Year = {1998},
    Abstract = {An increasing amount of interest has developed in VHF/UHF SAR applications. Unfortunately the VHF-UHF portion of the spectrum is already in heavy use by other services, such as television and mobile communications. Even in remote locations the interference power often exceeds receiver noise by many dB, becoming the limiting factor on system sensitivity and severely degrading the image quality. This paper addresses the problem of radio frequency (RF) interference and its impact on SAR imagery. Several RF interference suppression methods are described and discussed. These include spectral estimation and coherent subtraction algorithms, as well as various filter approaches. The least-mean-squared (LMS) adaptive filter is described in detail, and its effectiveness in suppressing RF interference is demonstrated on simulated data and on real P-band data.},
    Keywords = {SAR Processing, adaptive filters, adaptive signal processing, interference suppression, least mean squares methods, radar imaging, radar interference, synthetic aperture radar, LMS adaptive filter, P-Band, RF interference suppression, RFI Suppression, SAR imagery, VHF/UHF SAR applications, VHF/UHF synthetic aperture radar, coherent subtraction algorithms, filter approaches, image quality, interference power, least-mean-squared filter, radio frequency interference, receiver noise, spectral estimation},
    Owner = {ofrey},
    Pdf = {../../../docs/lordInggs98.pdf} 
    }
    




13. Carole E. Nahum. Autofocusing using multiscale local correlation. In Proc. SPIE, volume 3497, pages 21-30, 1998. Keyword(s): SAR Processing, Autofocus, SAR Autofocus, MoComp, Motion Compensation, Map-Drift Autofocus, airborne radar, radar imaging, synthetic aperture radar, SAR data, SAR images, X-band airborne SAR system, arbitrary residual phase error, local-quadratic map-drift autofocus, phase error estimation, quadratic errors, small data blocks, uncompensated phase errors, Antennas, Azimuth, Bandwidth, Doppler effect, Measurement uncertainty, Radar, Trajectory, autofocus, map-drift, motion compensation, motion errors, synthetic aperture radar.

    Abstract:

    Ground imaging using a Synthetic Aperture Radar (SAR) requires the knowledge of the antenna trajectory with a relative accuracy of a fraction of the wavelength upon an integration time of a few seconds. This information is not always available from inertial navigation unit especially in the airborne framework and must be recovered from the radar signal itself using the techniques known as autofocus. We describe in this paper an original method designed at ONERA for the registration of looks. We show how it applies to autofocusing. It improves the map-drift algorithm making it time variant thus allowing for the correction of low frequency trajectory errors, and not only velocity bias.

    
    

    @InProceedings{nahumSPIE1998Autofocus,
    author = {Nahum, Carole E.},
    booktitle = {Proc. SPIE},
    title = {Autofocusing using multiscale local correlation},
    year = {1998},
    pages = {21-30},
    volume = {3497},
    abstract = {Ground imaging using a Synthetic Aperture Radar (SAR) requires the knowledge of the antenna trajectory with a relative accuracy of a fraction of the wavelength upon an integration time of a few seconds. This information is not always available from inertial navigation unit especially in the airborne framework and must be recovered from the radar signal itself using the techniques known as autofocus. We describe in this paper an original method designed at ONERA for the registration of looks. We show how it applies to autofocusing. It improves the map-drift algorithm making it time variant thus allowing for the correction of low frequency trajectory errors, and not only velocity bias.},
    doi = {10.1117/12.331359},
    file = {:nahumSPIE1998Autofocus.pdf:PDF},
    keywords = {SAR Processing, Autofocus, SAR Autofocus, MoComp, Motion Compensation, Map-Drift Autofocus, airborne radar;radar imaging;synthetic aperture radar;SAR data;SAR images;X-band airborne SAR system;arbitrary residual phase error;local-quadratic map-drift autofocus;phase error estimation;quadratic errors;small data blocks;uncompensated phase errors;Antennas;Azimuth;Bandwidth;Doppler effect;Measurement uncertainty;Radar;Trajectory;autofocus;map-drift;motion compensation;motion errors;synthetic aperture radar},
    pdf = {../../../docs/nahumSPIE1998Autofocus.pdf},
    
    }
    




14. Stefan Nilsson and Lars-Erik Andersson. Application of Fast Backprojection Techniques for some Inverse Problems of Synthetic Aperture Radar. In Edmund G. Zelnio, editor, Algorithms for Synthetic Aperture Radar Imagery V, volume SPIE 3370, pages 62-72, 1998. Keyword(s): SAR Processing, Back-Projection, Fast Back-Projection, Quadtree Processing, Time-Domain Back-Projection, TDBP, Circular Averages, Wideband SAR, Focusing, Motion Compensation.

    Abstract:

    In certain radar imaging applications one encounters the problem of reconstructing a reflectivityfunction from information about its averages over circles with center on a straight line. A robust inversion method is afiltered backprojection method, similar to the one used in medical tomography. We will present a fast algorithm for this backprojection operator. Numerical examples are given.

    
    

    @InProceedings{NilssonAndersson98:Backprojection,
    Title = {{Application of Fast Backprojection Techniques for some Inverse Problems of Synthetic Aperture Radar}},
    Author = {Stefan Nilsson and Lars-Erik Andersson},
    Booktitle = {Algorithms for Synthetic Aperture Radar Imagery V},
    Editor = {Edmund G. Zelnio},
    Pages = {62-72},
    Url = {http://spie.org/scripts/abstract.pl?bibcode=1998SPIE%2e3370%2e%2e%2e62N&page=1&qs=spie},
    Volume = {SPIE 3370},
    Year = {1998},
    Abstract = {In certain radar imaging applications one encounters the problem of reconstructing a reflectivityfunction from information about its averages over circles with center on a straight line. A robust inversion method is afiltered backprojection method, similar to the one used in medical tomography. We will present a fast algorithm for this backprojection operator. Numerical examples are given.},
    Keywords = {SAR Processing, Back-Projection, Fast Back-Projection, Quadtree Processing, Time-Domain Back-Projection, TDBP, Circular Averages, Wideband SAR, Focusing, Motion Compensation},
    Pdf = {../../../docs/NilssonAndersson98.pdf} 
    }
    




15. Richard Rau and James H. McClellan. A Directional Image Decomposition for Ultra-Wideband SAR. In ICASSP '98, International Conference on Acoustics, Speech, and Signal Processing, volume 5, pages 2877-2880, May 1998. Keyword(s): SAR Processing, Back-Projection, Ultra-Wideband SAR, Directional Filterbanks, TDBP, Time-Domain Back-Projection.

    Abstract:

    This paper presents a theoretical analysis of the structure of wide angle, ultra-wideband SAR images formed by a constant integration angle backprojection image former. It is shown that the effects of the image former can be modeled as a filtering operation on the original data. Furthermore, SAR images for different squint angles can be obtained from the original images by directional filtering. As a result, it is shown that perfect reconstructing directional filterbanks can be used as a unitary transform between SAR images and a 3-D representation containing additional aspect-angle information. It is demonstrated, how this new representation can be used to enhance targets.

    
    

    @InProceedings{RauMcClellan98:Backproj,
    Title = {{A Directional Image Decomposition for Ultra-Wideband SAR}},
    Author = {Richard Rau and James H. McClellan},
    Booktitle = {ICASSP '98, International Conference on Acoustics, Speech, and Signal Processing},
    Month = May,
    Pages = {2877-2880},
    Volume = {5},
    Year = {1998},
    Abstract = {This paper presents a theoretical analysis of the structure of wide angle, ultra-wideband SAR images formed by a constant integration angle backprojection image former. It is shown that the effects of the image former can be modeled as a filtering operation on the original data. Furthermore, SAR images for different squint angles can be obtained from the original images by directional filtering. As a result, it is shown that perfect reconstructing directional filterbanks can be used as a unitary transform between SAR images and a 3-D representation containing additional aspect-angle information. It is demonstrated, how this new representation can be used to enhance targets.},
    Keywords = {SAR Processing, Back-Projection, Ultra-Wideband SAR, Directional Filterbanks, TDBP, Time-Domain Back-Projection},
    Pdf = {../../../docs/rauMcClellan98.pdf} 
    }
    




16. Andreas Reigber and Andreas Ulbricht. P-band repeat-pass interferometry with the DLR experimental SAR. In Geoscience and Remote Sensing Symposium Proceedings, 1998. IGARSS '98. 1998 IEEE International, volume 4, pages 1914-1916, 1998. Keyword(s): SAR Processing, airborne radar, geophysical techniques, remote sensing by radar, synthetic aperture radar, DLR experimental SAR, ESAR, P-Band, RF interference removal, RFI Suppression, SAR interferometry, Interferometry, UHF, geophysical measurement technique, ground parameters, land surface, radar remote sensing, repeat-pass interferometry, repeat-pass mode, surface topography, terrain mapping.

    Abstract:

    SAR interferometry is a powerful tool for the determination of surface topography and for estimation of ground parameters. In particular the analysis of different frequencies has the capability to provide a broad set of useful information. Therefore long wavelengths like the P-band of great interest, because they often show different interactions with scatterers than shorter wavelengths like the C-band. The authors address the implementation of a P-band repeat-pass mode for the DLR's experimental SAR (ESAR), including the problematic removal of RF-interferences in the data. Recent results on a test site in Solothurn/Switzerland are shown.

    
    

    @InProceedings{reigberUlbricht98:InterferoRFI,
    author = {Reigber, Andreas and Ulbricht, Andreas},
    booktitle = {Geoscience and Remote Sensing Symposium Proceedings, 1998. IGARSS '98. 1998 IEEE International},
    title = {P-band repeat-pass interferometry with the DLR experimental SAR},
    year = {1998},
    pages = {1914--1916},
    volume = {4},
    abstract = {SAR interferometry is a powerful tool for the determination of surface topography and for estimation of ground parameters. In particular the analysis of different frequencies has the capability to provide a broad set of useful information. Therefore long wavelengths like the P-band of great interest, because they often show different interactions with scatterers than shorter wavelengths like the C-band. The authors address the implementation of a P-band repeat-pass mode for the DLR's experimental SAR (ESAR), including the problematic removal of RF-interferences in the data. Recent results on a test site in Solothurn/Switzerland are shown.},
    keywords = {SAR Processing, airborne radar, geophysical techniques, remote sensing by radar, synthetic aperture radar, DLR experimental SAR, ESAR, P-Band, RF interference removal, RFI Suppression, SAR interferometry, Interferometry, UHF, geophysical measurement technique, ground parameters, land surface, radar remote sensing, repeat-pass interferometry, repeat-pass mode, surface topography, terrain mapping},
    owner = {ofrey},
    pdf = {../../../docs/reigberUlbricht98.pdf},
    url = {http://ieeexplore.ieee.org/iel4/5660/15207/00703693.pdf},
    
    }
    




17. Olle Seger, Magnus Herberthson, and Hans Hellsten. Real time SAR processing of low frequency ultra wide band radar data. In Proc. of EUSAR '98 - European Conference on Synthetic Aperture Radar, pages 489-492, May 1998. Keyword(s): SAR Processing, Back-Projection, Time-Domain Back-Projection, TDBP, Local Back-Projection, Real Time Operation, Ultra-Wideband SAR, FOPEN, Image processing, Ground Penetrating Radar, Low-Frequency SAR, Image Reconstruction, Radar Resolution, Parallel Processing.

    Abstract:

    CARABAS (Coherent All RAdio BAnd Sensing) is a synthetic aperture radar with high relative bandwidth. Furthermore, CARABAS operates at radio band frequencies, which enables the radar to penetrate foliage. In this paper, we propose and analyze a reconstruction algorithm suitable for parallel implementation. The core idea of the method is a subdivision of the radar raw data into subapertures, from which coarse resolution subimages can be reconstructed. These subimages are then distributed to the nodes of a powerful parallel computer in order to achieve fine resolution at real-time rate.

    
    

    @InProceedings{segerHerberthsonHellsten98:LocalBackprojection,
    Title = {Real time SAR processing of low frequency ultra wide band radar data},
    Author = {Seger, Olle and Herberthson, Magnus and Hellsten, Hans},
    Booktitle = {Proc. of EUSAR '98 - European Conference on Synthetic Aperture Radar},
    Month = {May},
    Pages = {489-492},
    Year = {1998},
    Abstract = {CARABAS (Coherent All RAdio BAnd Sensing) is a synthetic aperture radar with high relative bandwidth. Furthermore, CARABAS operates at radio band frequencies, which enables the radar to penetrate foliage. In this paper, we propose and analyze a reconstruction algorithm suitable for parallel implementation. The core idea of the method is a subdivision of the radar raw data into subapertures, from which coarse resolution subimages can be reconstructed. These subimages are then distributed to the nodes of a powerful parallel computer in order to achieve fine resolution at real-time rate.},
    Keywords = {SAR Processing, Back-Projection, Time-Domain Back-Projection, TDBP, Local Back-Projection, Real Time Operation, Ultra-Wideband SAR, FOPEN, Image processing; Ground Penetrating Radar, Low-Frequency SAR, Image Reconstruction, Radar Resolution, Parallel Processing},
    Owner = {ofrey},
    Pdf = {../../../docs/segerHerberthsonHellsten98.pdf} 
    }
    




18. David Small, Francesco Holecz, Erich Meier, and Daniel Nüesch. Absolute radiometric correction in rugged terrain: A plea for integrated radar brightness. In Proc. IEEE Int. Geosci. Remote Sens. Symp., volume 1, pages 330-332, 1998. Keyword(s): geophysical signal processing, geophysical techniques, radar imaging, remote sensing by radar, spaceborne radar, synthetic aperture radar, absolute radiometric correction, biomass estimation, geophysical measurement technique, integrated radar brightness, integrative faceted heteromorphic approach, land surface, multimode SAR imagery, multimode image comparison, radar remote sensing, radiometric normalisation, rugged terrain, terrain mapping, terrain-induced variation.

    Abstract:

    Rigorous intercomparison of multimode SAR imagery requires not

    
    

    @InProceedings{SmallHoleczMeierNuesch98:RadiometricCorrectionIGARSS,
    author = {Small, David and Holecz, Francesco and Meier, Erich and N{\"u}esch, Daniel},
    booktitle = {Proc. IEEE Int. Geosci. Remote Sens. Symp.},
    title = {Absolute radiometric correction in rugged terrain: A plea for integrated radar brightness},
    year = {1998},
    pages = {330--332},
    volume = {1},
    abstract = {Rigorous intercomparison of multimode SAR imagery requires not},
    keywords = {geophysical signal processing, geophysical techniques, radar imaging, remote sensing by radar, spaceborne radar, synthetic aperture radar, absolute radiometric correction, biomass estimation, geophysical measurement technique, integrated radar brightness, integrative faceted heteromorphic approach, land surface, multimode SAR imagery, multimode image comparison, radar remote sensing, radiometric normalisation, rugged terrain, terrain mapping, terrain-induced variation},
    owner = {ofrey},
    pdf = {../../../docs/SmallHoleczMeierNuesch98IGARSS.pdf},
    url = {http://ieeexplore.ieee.org/iel4/5660/15194/00702895.pdf},
    
    }
    




19. David Small, Francesco Holecz, Erich Meier, and Daniel Nüesch. Radiometric Normalization for Multimode Image Comparison. In Proc. of EUSAR '98 - European Conference on Synthetic Aperture Radar, pages 191-194, 1998. Keyword(s): SAR Processing, SAR Geocoding, Geocoding, Calibration, Radiometric Calibration, Radiometric Correction, Digital Elevation Model, Image Simulation, Terrain-Geocoding.

    Abstract:

    Intercomparison of backscatter collected by SAR sensors at heterogeneous radar look angles gives rise to highly variable ground areas being associated with each pixel location within a radar geometry (slant or ground range) image. Many elements within a digital elevation model (in map geometry) can be mapped to a single location in the radar image (range / Doppler coordinates). An image simulation technique uses a faceted high resolution elevation model to integrate all backscatter returned to each range and Doppler location in the radar image (incorporating knowledge of local radar shadow). Modelling the imaging process in this manner, a map of illuminated area is produced in radar geometry, and used to normalize the true backscatter returned by the radar sensor. Although radar shadow must be considered specially, no extraordinary treatment is required of layover regions, as they are correctly accounted for by integration of the illuminated area. The image simulation approach improves on the conventional consideration of 2D incidence angles, as the 3D configuration defining the illuminated area (in both the range and azimuth dimensions) is captured. RADARSAT images acquired over Switzerland are used to demonstrate the benefit of such normalization for thematic interpretation. A high resolution digital elevation model (DEM) with 25m pixel spacing is used as input to the image simulation. The deterioration of the normalization with progressively poorer input DEMs is studied empirically to gauge the required DEM resolution for acceptable normalization of images acquired over pre-alpine topography.

    
    

    @InProceedings{smallHoleczMeierNueesch98:RadiometricNorm,
    author = {David Small and Francesco Holecz and Erich Meier and Daniel N{\"u}esch},
    booktitle = {Proc. of EUSAR '98 - European Conference on Synthetic Aperture Radar},
    title = {Radiometric Normalization for Multimode Image Comparison},
    year = {1998},
    pages = {191-194},
    abstract = {Intercomparison of backscatter collected by SAR sensors at heterogeneous radar look angles gives rise to highly variable ground areas being associated with each pixel location within a radar geometry (slant or ground range) image. Many elements within a digital elevation model (in map geometry) can be mapped to a single location in the radar image (range / Doppler coordinates). An image simulation technique uses a faceted high resolution elevation model to integrate all backscatter returned to each range and Doppler location in the radar image (incorporating knowledge of local radar shadow). Modelling the imaging process in this manner, a map of illuminated area is produced in radar geometry, and used to normalize the true backscatter returned by the radar sensor. Although radar shadow must be considered specially, no extraordinary treatment is required of layover regions, as they are correctly accounted for by integration of the illuminated area. The image simulation approach improves on the conventional consideration of 2D incidence angles, as the 3D configuration defining the illuminated area (in both the range and azimuth dimensions) is captured. RADARSAT images acquired over Switzerland are used to demonstrate the benefit of such normalization for thematic interpretation. A high resolution digital elevation model (DEM) with 25m pixel spacing is used as input to the image simulation. The deterioration of the normalization with progressively poorer input DEMs is studied empirically to gauge the required DEM resolution for acceptable normalization of images acquired over pre-alpine topography.},
    keywords = {SAR Processing, SAR Geocoding, Geocoding, Calibration, Radiometric Calibration, Radiometric Correction, Digital Elevation Model, Image Simulation, Terrain-Geocoding},
    owner = {ofrey},
    pdf = {../../../docs/smallHoleczMeierNueesch98.pdf},
    url = {http://www.geo.uzh.ch/publications/daves/1998/Small_EUSAR_1998.pdf},
    
    }
    




20. Mehrdad Soumekh. Range Stacking: An Interpolation-free SAR Reconstruction Algorithm. In Edmund G. Zelnio, editor, Algorithms for Synthetic Aperture Radar Imagery V, volume SPIE 3370, pages 13-24, 1998. Keyword(s): SAR Processing, Range Stacking Algorithm, Wavefront Reconstruction, Wavenumber Domain Algorithm, omega-k, Back-Projection, Time-Domain Back-Projection, TDBP, Wideband SAR, Squinted SAR, FOPEN, Motion Compensation.

    Abstract:

    A method for digital image formation in Synthetic Aperture Radar (SAR) systems is presented. The proposed approach is based on the wavefront reconstruction theory for SAR imaging systems. However, this is achieved without image formation in the spatial frequency domain of the target function which requires interpolation. The proposed method forms the target function at individual range points within the radar range swath; this is referred to as range stacking. The range stacking reconstruction method is applicable in stripmap and spotlight (broadside and squint) SAR systems. Results using a wide-beamwidth FOliage PENetrating (FOPEN) SAR database are provided, and the effect of beamwidth filtering on the signature of moving targets in the imaging scene is shown.

    
    

    @InProceedings{Soumekh98:,
    Title = {{Range Stacking: An Interpolation-free SAR Reconstruction Algorithm}},
    Author = {Mehrdad Soumekh},
    Booktitle = {Algorithms for Synthetic Aperture Radar Imagery V},
    Editor = {Edmund G. Zelnio},
    Pages = {13-24},
    Url = {http://spiedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PSISDG003370000001000013000001&idtype=cvips&gifs=yes},
    Volume = {SPIE 3370},
    Year = {1998},
    Abstract = {A method for digital image formation in Synthetic Aperture Radar (SAR) systems is presented. The proposed approach is based on the wavefront reconstruction theory for SAR imaging systems. However, this is achieved without image formation in the spatial frequency domain of the target function which requires interpolation. The proposed method forms the target function at individual range points within the radar range swath; this is referred to as range stacking. The range stacking reconstruction method is applicable in stripmap and spotlight (broadside and squint) SAR systems. Results using a wide-beamwidth FOliage PENetrating (FOPEN) SAR database are provided, and the effect of beamwidth filtering on the signature of moving targets in the imaging scene is shown.},
    Keywords = {SAR Processing, Range Stacking Algorithm, Wavefront Reconstruction, Wavenumber Domain Algorithm, omega-k, Back-Projection, Time-Domain Back-Projection, TDBP, Wideband SAR, Squinted SAR, FOPEN, Motion Compensation},
    Pdf = {../../../docs/Soumekh98.pdf} 
    }
    




21. D.G. Thompson, J.S. Bates, D.V. Arnold, David G. Long, and A. Robertson. Range dependent phase gradient autofocus. In IEEE International Geoscience and Remote Sensing Symposium Proceedings, IGARSS '98, volume 5, pages 2634-2636, July 1998. Keyword(s): SAR Processing, Autofocus, Phase Gradient Autofocus, PGA, Range-dependent.

    Abstract:

    The Phase Gradient Autofocus (PGA) algorithm has been widely used in Spotlight Synthetic Aperture Radar (SAR) to remove motion-induced blurs in the images. The PGA algorithm has been proven to be a superior autofocus method. PGA assumes a narrow beam, which is valid for most SAR systems. However, lower altitude SAR have large range dependencies that cannot be ignored. A new phase estimator for PGA is introduced and extended to allow range dependence. An ERS-1 image of Death Valley is used in simulations comparing the new estimator to the widely used maximum likelihood approach and in demonstrating the range-dependent PGA algorithm.

    
    

    @InProceedings{thompsonBatesArnoldLong1998:PGA,
    Title = {Range dependent phase gradient autofocus},
    Author = {Thompson, D.G. and Bates, J.S. and Arnold, D.V. and Long, David G. and Robertson, A.},
    Booktitle = {IEEE International Geoscience and Remote Sensing Symposium Proceedings, IGARSS '98},
    Doi = {10.1109/IGARSS.1998.702303},
    Month = jul,
    Pages = {2634--2636},
    Url = {http://ieeexplore.ieee.org/iel4/5660/15200/00702303.pdf},
    Volume = {5},
    Year = {1998},
    Abstract = {The Phase Gradient Autofocus (PGA) algorithm has been widely used in Spotlight Synthetic Aperture Radar (SAR) to remove motion-induced blurs in the images. The PGA algorithm has been proven to be a superior autofocus method. PGA assumes a narrow beam, which is valid for most SAR systems. However, lower altitude SAR have large range dependencies that cannot be ignored. A new phase estimator for PGA is introduced and extended to allow range dependence. An ERS-1 image of Death Valley is used in simulations comparing the new estimator to the widely used maximum likelihood approach and in demonstrating the range-dependent PGA algorithm.},
    Keywords = {SAR Processing, Autofocus, Phase Gradient Autofocus, PGA, Range-dependent},
    Owner = {ofrey},
    Pdf = {../../../docs/thompsonBatesArnoldLong1998.pdf} 
    }
    

Miscellaneous

1. Clint Slatton. Improving Segmented INSAR Processing Using Presumming. , 1998. Keyword(s): SAR Processing, InSAR, TOPSAR, Presumming, Range-Doppler Algorithm, Azimuth Processing, omega-k Algorithm.

   Abstract:

   Literature Survey

   Comments:

   +/- Not much on presumming, but generally a good introduction to some SAR concepts.

   
   

   @Unpublished{Sla98:Improving,
   Title = {{Improving Segmented INSAR Processing Using Presumming}},
   Author = {Clint Slatton},
   Url = {http://www.ae.utexas.edu/~slatton/},
   Year = {1998},
   Abstract = {Literature Survey},
   Comments = {+/- Not much on presumming, but generally a good introduction to some SAR concepts.},
   Keyword = {SAR Processing, InSAR, TOPSAR, Presumming, Range-Doppler Algorithm, Azimuth Processing, omega-k Algorithm},
   Owner = {ofrey},
   Pdf = {../../../docs/slaton98.pdf} 
   }
   

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This collection of SAR literature is far from being complete.
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