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See detailPresentation of CSL Signal Processing Laboratory - First STAR Workshop on 15/09/2017
Orban, Anne ULiege

Scientific conference (2017, September 15)

Presentation of the Signal Processing laboratory of the Centre Spatial de Liège

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See detailSplit-Band Interferometry-Assisted Phase Unwrapping for the Phase Ambiguities Correction
Libert, Ludivine ULiege; De Rauw, Dominique ULiege; d'Oreye, Nicolas et al

in Remote Sensing (2017), 9(9),

Split-Band Interferometry (SBInSAR) exploits the large range bandwidth of the new generation of synthetic aperture radar (SAR) sensors to process images at subrange bandwidth. Its application to an ... [more ▼]

Split-Band Interferometry (SBInSAR) exploits the large range bandwidth of the new generation of synthetic aperture radar (SAR) sensors to process images at subrange bandwidth. Its application to an interferometric pair leads to several lower resolution interferograms of the same scene with slightly shifted central frequencies. When SBInSAR is applied to frequency-persistent scatterers, the linear trend of the phase through the stack of interferograms can be used to perform absolute and spatially independent phase unwrapping. While the height computation has been the main concern of studies on SBInSAR so far, we propose instead to use it to assist conventional phase unwrapping. During phase unwrapping, phase ambiguities are introduced when parts of the interferogram are separately unwrapped. The proposed method reduces the phase ambiguities so that the phase can be connected between separately unwrapped regions. The approach is tested on a pair of TerraSAR-X spotlight images of Copahue volcano, Argentina. In this framework, we propose two new criteria for the frequency-persistent scatterers detection, based respectively on the standard deviation of the slope of the linear regression and on the phase variance stability, and we compare them to the multifrequency phase error. Both new criteria appear to be more suited to our approach than the multifrequency phase error. We validate the SBInSAR-assisted phase unwrapping method by artificially splitting a continuous phase region into disconnected subzones. Despite the decorrelation and the steep topography affecting the volcanic test region, the expected phase ambiguities are successfully recovered whatever the chosen criterion to detect the frequency-persistent scatterers. Comparing the aspect ratio of the distributions of the computed phase ambiguities, the analysis shows that the phase variance stability is the most efficient criterion to select stable targets and the slope standard deviation gives satisfactory results. [less ▲]

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See detailThe Split-Band Interferometry Approach to Determine the Phase Unwrapping Offset
Libert, Ludivine ULiege; De Rauw, Dominique ULiege; d'Oreye, Nicolas et al

Poster (2017, June)

This poster presents an approach based on the Split-Band Interferometry to solve the ambiguities introduced during the phase unwrapping of separate regions.

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See detailA TOPSAR Processor based on the Omega-K Algorithm: Evaluation with Sentinel-1 Data
Kirkove, Murielle ULiege; Orban, Anne ULiege; De Rauw, Dominique ULiege et al

in A TOPSAR Processor based on the Omega-K Algorithm: Evaluation with Sentinel-1 Data (2016, June)

This paper presents a processor for the TOPS (Terrain Observation by Progressive Scans) imaging mode. TOPS signals have two characteristics that make the use of Stripmap SAR processors inconvenient, i.e ... [more ▼]

This paper presents a processor for the TOPS (Terrain Observation by Progressive Scans) imaging mode. TOPS signals have two characteristics that make the use of Stripmap SAR processors inconvenient, i.e., azimuth frequency and azimuth time foldings. This paper describes a processor based on the Omega-K (Ω-k) algorithm, combined with pre-processing by frequency unfolding and post-processing by time unfolding. Raw data acquired by Sentinel-1 have been used to assess the quality of image reconstruction [less ▲]

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See detailVérification expérimentale de modèles opto-thermo-élastiques simulés avec le logiciel OOFELIE Multiphysics
Mazzoli, Alexandra ULiege; Saint-Georges, Philippe; Orban, Anne ULiege et al

in 12ème colloque international francophone sur les Méthodes et Techniques Optiques pour l'Industrie (2011, November)

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See detailExperimental validation of opto-thermo-elastic modeling in OOFELIE Multiphysics
Mazzoli, Alexandra ULiege; Saint-Georges, Philippe; Orban, Anne ULiege et al

in SPIE, Optical Systems Design (Marseille 5-8 septembre 2011) (2011)

The objective of this work is to demonstrate the correlation between a simple laboratory test bench case and the predictions of the Oofelie MultiPhysics software in order to deduce modelling guidelines ... [more ▼]

The objective of this work is to demonstrate the correlation between a simple laboratory test bench case and the predictions of the Oofelie MultiPhysics software in order to deduce modelling guidelines and improvements. For that purpose two optical systems have been analysed. The first one is a spherical lens fixed in an aluminium barrel, which is the simplest structure found in an optomechanical system. In this study, material characteristics are assumed to be well known: BK7 and aluminium have been retained. Temperature variations between 0 and +60°C from ambient have been applied to the samples. The second system is a YAG laser bar heated by means of a dedicated oven. For the two test benches thermo-elastic distortions have been measured using a Fizeau interferometer. This sensor measures wavefront error in the range of 20 nm to 1 μm without physical contact with the optomechanical system. For the YAG bar birefringence and polarization measurements have also been performed using a polarimetric bench. The tests results have been compared to the predictions obtained by Oofelie MultiPhysics which is a multiphysics toolkit treating coupled problems of optics, mechanics, thermal physics, electricity, electromagnetism, acoustics and hydrodynamics. From this comparison modelling guidelines have been issued with the aim of improving the accuracy of computed thermo-elastic distortions and their impact on the optical performances. [less ▲]

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See detailWide band SAR sub-band splitting and inter-band coherence measurements
De Rauw, Dominique ULiege; Orban, Anne ULiege; Barbier, Christian ULiege

in Remote Sensing Letters (2010), 1(3), 133-140

Range resolution of SAR images is determined by transmitted radar signal bandwidth. Most recent SAR sensors use wide band signals in order to achieve metric range resolution, whereas metric azimuth ... [more ▼]

Range resolution of SAR images is determined by transmitted radar signal bandwidth. Most recent SAR sensors use wide band signals in order to achieve metric range resolution, whereas metric azimuth resolution can be achieved in spotlight mode. As an example, ENVISAT ASAR sensor uses a 15-MHz bandwidth chirp whereas TerraSAR-X spotlight mode uses signals having a 150-MHz bandwidth leading to a potentially 10 times higher resolution. One can also take advantage of wide band to split the full band into sub-bands and generate several lower resolution images from a single acquisition, each being centred on slightly different frequencies. These sub-images can then be used in a classical interferometric process to measure inter-band coherence of a given scene. This inter-band coherence reveals scatterers keeping a stable-phase behaviour along with frequency shift. A simple coherence model derived from Zebker model for randomly distributed surface scatterers is proposed. Examples are presented, showing that scatterers can have a behaviour that deviates from the model, leading to a new information channel. [less ▲]

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See detailInter-band Coherence of Split Wide Band SAR Images; A Potentially New Information Channel
De Rauw, Dominique ULiege; Orban, Anne ULiege; Barbier, Christian ULiege

in EARSel Newsletter (2009), 79

Recently-launched SAR sensors like TerraSAR-X or CosmoSkyMed are equipped with wide bandwidth radar signal emitters. Working at large bandwidth allows reaching metric range resolution, which combined with ... [more ▼]

Recently-launched SAR sensors like TerraSAR-X or CosmoSkyMed are equipped with wide bandwidth radar signal emitters. Working at large bandwidth allows reaching metric range resolution, which combined with spotlight mode, leads to Very High Resolution (VHR) SAR imagery. One can also take advantage of this wide band to split it into sub-bands and generate several lower resolution images from the same master one, each centered on a slightly different cen- tral frequency. These sub-images can then be used in a classical interferometric process to estimate inter- band coherence of a given scene. This inter-band coherence reveals scatterers keeping a stable phase behaviour along with frequency shift. In this paper, a simple model derived from Zebker model for randomly distributed surface scatterers is proposed and examples are pre- sented showing that scatterers can have a behaviour that deviates from the model, leading to a new information channel. [less ▲]

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See detailOptical calibration of the FUV spectrographic imager for the IMAGE mission
Habraken, Serge ULiege; Houbrechts, Yvette ULiege; Renotte, Etienne ULiege et al

in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (1999, October 01)

The FUV Spectrographic Imager for IMAGE is simultaneously imaging auroras at 1218 and 1358 angstrom. It is designed to efficiently reject the Lyman-(alpha) emission line at 1215.7 angstrom. This paper ... [more ▼]

The FUV Spectrographic Imager for IMAGE is simultaneously imaging auroras at 1218 and 1358 angstrom. It is designed to efficiently reject the Lyman-(alpha) emission line at 1215.7 angstrom. This paper describes the optical calibration. The content is: 1) field of view calibration: detector pixels location with respect to the reference optical cube; distortion matrix used to computer the TDI. b) Radiometric calibration: detector response and linearity; instrument throughput according to its clear aperture and mirror reflection lost; response vs. wavelength and band-rejection certification. [less ▲]

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See detailDesign and verification of the Far Ultraviolet Spectrographic Imager (FUV-SI) for the IMAGE mission
Renotte, Etienne ULiege; Habraken, Serge ULiege; Rochus, Pierre ULiege et al

in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (1998, November 01)

The IMAGE FUV-SI is simultaneously imaging auroras at 121.8 nm and 135.8 nm. The spectrograph design challenge is the efficient rejection of the intense Lyman-alpha emission at 121.6 nm while passing its ... [more ▼]

The IMAGE FUV-SI is simultaneously imaging auroras at 121.8 nm and 135.8 nm. The spectrograph design challenge is the efficient rejection of the intense Lyman-alpha emission at 121.6 nm while passing its Doppler-shifted component at 121.8 nm. The FUV-SI opto-mechanical design, analysis integration, and verification of performances against environment are discussed in this paper. In absence of STM environmental constraints at subsystem levels are derived analytically from F.E.M. and used for pre-qualifying optical subsystems. [less ▲]

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