References of "Orban, Anne"
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See detailEmpirical Removal of Tides and Inverse Barometer Effect on DInSAR From Double DInSAR and a Regional Climate Model
Glaude, Quentin ULiege; Amory, Charles ULiege; Berger, Sophie et al

in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing (2020), 13

Ice shelves—the floating extensions of the Antarctic ice sheet—regulate the Antarctic contribution to sea-level rise by restraining the grounded ice flowing from upstream. Therefore, ice-shelf change (e.g ... [more ▼]

Ice shelves—the floating extensions of the Antarctic ice sheet—regulate the Antarctic contribution to sea-level rise by restraining the grounded ice flowing from upstream. Therefore, ice-shelf change (e.g., ice-shelf thinning) results in accelerated ice discharge into the ocean, which has a direct effect on sea level. Studying ice-shelf velocity allows the monitoring of the ice shelves’ stability and evolution. Differential synthetic aperture radar interferometry (DInSAR) is a common technique from which highly accurate velocity maps can be inferred at high resolution. Because ice shelves are afloat, small sea-level changes—i.e., ocean tides and varying atmospheric pressure (aka inverse barometer effect) lead to vertical displacements. If not accounted for in the interferometric process, these effects will induce a strong bias in the horizontal velocity estimation. In this article, we present an empirical DInSAR correction technique from geophysical models and double DInSAR, with a study on its variance propagation. The method is developed to be used at large coverage on short timescales, essential for the near-continuous monitoring of rapidly changing areas on polar ice sheets. We used Sentinel-1 SAR acquisitions in interferometric wide and extra -wide swath modes. The vertical interferometric bias is estimated using a regional climate model (MAR) and a tide model (CATS2008). The study area is located on the Roi Baudouin Ice Shelf in Dronning Maud Land, East Antarctica. Results show a major decrease (67 m ⋅ a −1 ) in the vertical-induced displacement bias. [less ▲]

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See detailMUZUBI – Advanced phase unwrapping using split-band interferometry
Defrere, Denis ULiege; Radioti, Aikaterini ULiege; De Rauw, Dominique ULiege et al

Scientific conference (2019, November 28)

Absolute phase retrieval is a mandatory pre-requisite for accurate topographic measurements from SAR interferometric data. Because they use the phase of a starting point as a reference level, classical ... [more ▼]

Absolute phase retrieval is a mandatory pre-requisite for accurate topographic measurements from SAR interferometric data. Because they use the phase of a starting point as a reference level, classical phase unwrapping techniques usually fail to connect regions separated by non-coherent areas and require additional corrections to produce continuous phase maps which are consistent with the ground truth. A technique commonly used for that purpose is split-band interferometry, also known as multi chromatic analysis (MCA), which exploits the large range bandwidth of SAR sensors such as TerraSAR-X / TanDEM-X. The idea behind this technique is that the absolute phase is proportional to the intercept and slope of the spectrally-dispersed phase across individual sub-bands. Previous MCA analysis generally focused on the search of carefully-chosen targets, called frequency-persistent scatterers, which are used to estimate the global phase offset of the entire disconnected region. In this study, we take another approach and argue that all pixels in each independently-unwrapped region carry useful information that can be used to improve the precision on the absolute phase. In the context of the MUZUBI project, we have applied this idea to TerraSAR-X / TanDEM-X and SENTINEL images and investigated the effect of sensor bandwidth, mean coherence across the region, and region size on the precision of the computed absolute phase. [less ▲]

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See detailFundamental Limit of Absolute Phase Retrieval with Split-Band Interferometry: Application to TerraSAR-X / TanDEM-X and SENTINEL Images
Defrere, Denis ULiege; Radioti, Aikaterini ULiege; Libert, Ludivine et al

Scientific conference (2019, October 24)

Accurate topographic and deformation measurements from SAR interferometry require to correctly unwrap the phase. However, classical phase unwrapping often fails at connecting different regions separated ... [more ▼]

Accurate topographic and deformation measurements from SAR interferometry require to correctly unwrap the phase. However, classical phase unwrapping often fails at connecting different regions separated by low coherence. This results in phase jumps, difficult to correct or even detect without proper ground measurements. One solution consists in using the topographic and deformation phase dependence with the wavelength. Using large bandwidth SAR acquisitions such as TerraSAR-X Spotlight images, we can apply split-band interferometry (SBInSAR) in order to produce different interferograms with slightly different center-frequencies. The absolute topographic phase is then proportional to the slope of individuals split-band interferograms. Previous MCA analysis generally focused on the search of carefully-chosen targets, called frequency-persistent scatterers (PSf). If they exist, these PSfs could be used to estimate the global phase offset of the entire disconnected region. Here, we take another approach and argue that all pixels in each independently-unwrapped region carry useful information on the absolute phase. All this information can finally be used to improve the precision on the absolute phase. In the context of the MUZUBI project, we have applied this idea to TerraSAR-X / TanDEM-X, CSK, and SENTINEL images. We investigated the effect of sensor bandwidth, mean coherence across the region, and region size on the precision of the computed absolute phase. The technique is also compared with the results of the SRTM digital elevation model. In the end, we derived the fundamental limits of applicability of split-band interferometry. [less ▲]

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See detailSplit-band SAR Interferometry For Vessel Tracking: Application On Sentinel-1 Data
Kirkove, Murielle ULiege; De Rauw, Dominique ULiege; Orban, Anne ULiege

Poster (2019, May 15)

Most recent Synthetic Aperture Radar (SAR) sensors use wide band signals to achieve metric range resolution. One can take advantage of this wide band to split a single acquisition into sub-bands and ... [more ▼]

Most recent Synthetic Aperture Radar (SAR) sensors use wide band signals to achieve metric range resolution. One can take advantage of this wide band to split a single acquisition into sub-bands and generate several lower-resolution images, centered on slightly different frequencies, performing so a SAR spectral analysis. One application of this process is the vessel detection based on spectral coherence analysis. We present a processing technique of vessel detection using SAR data, combining spectral coherence processing and Constant False Alarm Rate (CFAR) algorithm. The control of open seas areas or marine protected areas (MPAs) is usually performed based on the Automated Identification System (AIS) embarked within most of the vessels. The proposed technique handles a comparison with AIS data allowing to determine the ratio of non-cooperative vessels (or not equipped with AIS) within an area. We performed experiments on SAR data acquired on the Libyan Sea and we compared the results with the ones obtained by the SNAP “Ocean feature” tool, commonly used by the Remote Sensing community. [less ▲]

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See detailRemoving Tides and Inverse Barometer Effect on DInSAR of Antarctic Ice Shelves
Glaude, Quentin; Glaude, Quentin ULiege; Berger, Sophie et al

Conference (2019, April 11)

Surface displacements are of particular interest for characterizing the dynamics of Antarctic ice shelves. Differential Synthetic Aperture Radar Interferometry (DInSAR) is a common technique from which ... [more ▼]

Surface displacements are of particular interest for characterizing the dynamics of Antarctic ice shelves. Differential Synthetic Aperture Radar Interferometry (DInSAR) is a common technique from which high-resolution velocity maps can be inferred at high accuracy. However, though vertical displacement may be useful in some contexts, the main component of interest is the horizontal velocity when analyzing ice fluxes. Since SAR sensors are side-looking, it is the vector sum of both the vertical and horizontal components along the line of sight (LOS) that can be measured, creating some ambiguity in separating the two elements. Impacted by ocean tides and inverse barometer effect (IBE), ice shelves are subject to a vertical bias to be removed. Here, we present an empirical technique using Sentinel-1 radar satellite and regional models to estimate and remove the corresponding bias and show preliminary results on the Roi Baudouin Ice Shelf (RBIS) in Dronning Maud Land (Antarctica). [less ▲]

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See detailEmpirical Correction of Tides and Inverse Barometer Effect Phase Components from Double Dinsar and Regional Models
Glaude, Quentin ULiege; Berger, Sophie; Amory, Charles ULiege et al

Poster (2019)

Surface displacements are of particular interest for characterizing the dynamics of Antarctic ice shelves. Differential Synthetic Aperture Radar Interferometry (DInSAR) is a common technique from which ... [more ▼]

Surface displacements are of particular interest for characterizing the dynamics of Antarctic ice shelves. Differential Synthetic Aperture Radar Interferometry (DInSAR) is a common technique from which high-resolution velocity maps can be inferred at high accuracy. However, though vertical displacement may be useful in some contexts, the main component of interest is the horizontal velocity when analyzing ice fluxes. Since SAR sensors are side-looking, it is the vector sum of both the vertical and horizontal components along the line of sight (LOS) that can be measured, creating some ambiguity in separating the two elements. Impacted by ocean tides and inverse barometer effect (IBE), ice shelves are subject to a vertical bias to be removed. Here, we present an empirical technique using Sentinel-1 radar satellite and regional models to estimate and remove the corresponding bias and show preliminary results on the Roi Baudouin Ice Shelf (RBIS) in Dronning Maud Land (Antarctica). [less ▲]

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See detailWater Vapor Vertical Profiles on Mars in Dust Storms Observed by TGO/NOMAD
Aoki, Shohei ULiege; Vandaele, A. C.; Daerden, F. et al

in Journal of Geophysical Research: Planets (2019), 124(12), 3482-3497

It has been suggested that dust storms efficiently transport water vapor from the near-surface to the middle atmosphere on Mars. Knowledge of the water vapor vertical profile during dust storms is ... [more ▼]

It has been suggested that dust storms efficiently transport water vapor from the near-surface to the middle atmosphere on Mars. Knowledge of the water vapor vertical profile during dust storms is important to understand water escape. During Martian Year 34, two dust storms occurred on Mars: a global dust storm (June to mid-September 2018) and a regional storm (January 2019). Here we present water vapor vertical profiles in the periods of the two dust storms (Ls = 162–260° and Ls = 298–345°) from the solar occultation measurements by Nadir and Occultation for Mars Discovery (NOMAD) onboard ExoMars Trace Gas Orbiter (TGO). We show a significant increase of water vapor abundance in the middle atmosphere (40–100 km) during the global dust storm. The water enhancement rapidly occurs following the onset of the storm (Ls~190°) and has a peak at the most active period (Ls~200°). Water vapor reaches very high altitudes (up to 100 km) with a volume mixing ratio of ~50 ppm. The water vapor abundance in the middle atmosphere shows high values consistently at 60°S-60°N at the growth phase of the dust storm (Ls = 195°–220°), and peaks at latitudes greater than 60°S at the decay phase (Ls = 220°–260°). This is explained by the seasonal change of meridional circulation: from equinoctial Hadley circulation (two cells) to the solstitial one (a single pole-to-pole cell). We also find a conspicuous increase of water vapor density in the middle atmosphere at the period of the regional dust storm (Ls = 322–327°), in particular at latitudes greater than 60°S. [less ▲]

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See detailMethane on Mars: New insights into the sensitivity of CH 4 with the NOMAD/ExoMars spectrometer through its first in-flight calibration
Liuzzi, G.; Villanueva, G. L.; Mumma, M. J. et al

in Icarus (2019), 321

The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and ... [more ▼]

The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibration was achieved, together with its variability due to thermal effects on the grating. The AOTF properties and transfer function were also quantified, and we developed and tested a realistic method to compute the spectral continuum transmitted through the coupled grating and AOTF system. The calibration results enabled unprecedented insights into the important problem of the sensitivity of NOMAD to methane abundances in the atmosphere. We also deeply characterized its performance under realistic conditions of varying aerosol abundances, diverse albedos and changing illumination conditions as foreseen over the nominal mission. The results show that, in low aerosol conditions, NOMAD single spectrum, 1σ sensitivity to CH 4 is around 0.33 ppbv at 20 km of altitude when performing solar occultations, and better than 1 ppbv below 30 km. In dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir geometry, results demonstrate that NOMAD will be able to produce seasonal maps of CH 4 with a sensitivity around 5 ppbv over most of planet's surface with spatial integration over 5 × 5° bins. Results show also that such numbers can be improved by a factor of ~10 to ~30 by data binning. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate. © 2018 Elsevier Inc. [less ▲]

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See detailOn the characterization of frequency-persistent scatterers in Split-Band Interferometry
Libert, Ludivine ULiege; De Rauw, Dominique ULiege; d'Oreye, Nicolas et al

Conference (2018, July 24)

Split-Band Interferometry (SBInSAR) requires the presence of reliable frequency-persistent scatterers within the studied scene. However, the physical nature of such reflectors is still poorly known. In ... [more ▼]

Split-Band Interferometry (SBInSAR) requires the presence of reliable frequency-persistent scatterers within the studied scene. However, the physical nature of such reflectors is still poorly known. In this work, we perform a temporal analysis over the region of the Virunga Volcanic Province (Democratic Republic of Congo - DRC) and we show that frequency-persistent scatterers are not necessarily stable over time. We study and quantify the effect of the range resolution loss due to the bandwidth degradation in the SBInSAR process. Finally, radiometric information and spectral coherence are used to show that frequency-persistent scatterers cannot be associated to a specific scattering mechanism. [less ▲]

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See detailSplit-Band SAR and Split Band InSAR principle and applications
De Rauw, Dominique ULiege; Kirkove, Murielle ULiege; Libert, Ludivine ULiege et al

Poster (2018, April 19)

Most recent SAR sensors use wide band signals to achieve metric range resolution. One can also take advantage of wide band to split it into sub-bands and generate several lower-resolution images, centered ... [more ▼]

Most recent SAR sensors use wide band signals to achieve metric range resolution. One can also take advantage of wide band to split it into sub-bands and generate several lower-resolution images, centered on slightly different frequencies, from a single acquisition (Bovenga & al. 2014). This process, named Multi Chromatic Analysis (MCA) corresponds to performing a spectral analysis of SAR images. From this spectral analysis, three potential applications are shown. First, this splitting allows performing a spectral analysis of observed scatterers. Spectral coherence is derived by computing the coherence between sub-images issued from a single SAR acquisition. It was shown that in the presence of a random distribution of surface scatterers, spectral coherence is proportional to sub-band intersection of sub-images. This model is fully verified when observing spectral coherence on open seas areas. If the scatterers distribution departs from this distribution, like for manmade structures, spectral coherence may be preserved to a certain degree and allows discriminating vessels from see clutter even in case of high sea state. This property can be used to perform vessel detection (Derauw & al., 2010). Second, Split-Band SAR interferometry (SBInSAR) is also based on this spectral analysis performed on each image of an InSAR pair, yielding a stack of sub-band interferograms. Scatterers keeping a coherent behaviour in each sub- band interferogram show a phase that varies linearly with the carrier frequency, the slope being proportional to the absolute optical path difference. This potentially solves the problems of phase unwrapping on a pixel-per-pixel basis (Libert & al.). Third, unwrapping classically two sub-band interferograms allows getting two phases of a same scene and same ionospheric components. Since these two components behave differently with frequency, SBInSAR allows discriminating both and remove the ionospheric artifacts if presents (Gomba & al. 2016, Furuya & al. 2016). [less ▲]

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See detailEO_Regions_Science: Basic Research in support of EO_Regions!
Orban, Anne ULiege; Barbier, Christian ULiege; Billen, Roland ULiege et al

Conference (2018, January)

Detailed reference viewed: 56 (10 ULiège)
See detailRAPAS Close range aerial sensing of soils for improved remote sennsing products
Lambot; Van Oost; Orban, Anne ULiege et al

Conference (2018)

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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 detailStudy of a Passive Companion Micro-Satellite to the SAOCOM-1B Satellite of Argentina, for Bistatic and Interferometric SAR Applications
Barbier, Christian ULiege; De Rauw, Dominique ULiege; Orban, Anne ULiege et al

in Spie (Ed.) Proceedings SPIE Remote Sensing Conference 9241 Sensors, Systems, and Next-Generation Satellites (2014, September)

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See detailDetermining Tree Height by Polarimetric SAR Interferometry: Methodology
Orban, Anne ULiege; Barbier, Christian ULiege; De Rauw, Dominique ULiege

Poster (2012, September)

This poster presents the development of tools for extraction of tree height estimates from SARAT data using polarimetric SAR interferometry (PolInSAR) techniques: theoretical and practical expertise in ... [more ▼]

This poster presents the development of tools for extraction of tree height estimates from SARAT data using polarimetric SAR interferometry (PolInSAR) techniques: theoretical and practical expertise in canopy height extraction using advanced PolInSAR techniques, PolInSAR tool tailored to SAOCOM and SARAT specificities allowing these estimates to be made, and finally PolInSAR products and canopy height estimates over the test site of interest. [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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