Publications of Christian Barbier
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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 detailMonitoring the Recent Activity of Landslides in the Mailuu-Suu Valley (Kyrgyzstan) Using Radar and Optical Remote Sensing Techniques
Piroton, Valentine ULiege; Schlögel, Romy; Barbier, Christian ULiege et al

in Geosciences (2020), 10(5),

Central Asian mountain regions are prone to multiple types of natural hazards, often causing damage due to the impact of mass movements. In spring 2017, Kyrgyzstan suffered significant losses from a ... [more ▼]

Central Asian mountain regions are prone to multiple types of natural hazards, often causing damage due to the impact of mass movements. In spring 2017, Kyrgyzstan suffered significant losses from a massive landslide activation event, during which also two of the largest deep-seated mass movements of the former mining area of Mailuu-Suu—the Koytash and Tektonik landslides—were reactivated. This study consists of the use of optical and radar satellite data to highlight deformation zones and identify displacements prior to the collapse of Koytash and to the more superficial deformation on Tektonik. Especially for the first one, the comparison of Digital Elevation Models of 2011 and 2017 (respectively, satellite and unmanned aerial vehicle (UAV) imagery-based) highlights areas of depletion and accumulation, in the scarp and near the toe, respectively. The Differential Synthetic Aperture Radar Interferometry analysis identified slow displacements during the months preceding the reactivation in April 2017, indicating the long-term sliding activity of Koytash and Tektonik. This was confirmed by the computation of deformation time series, showing a positive velocity anomaly on the upper part of both landslides. Furthermore, the analysis of the Normalized Difference Vegetation Index revealed land cover changes associated with the sliding process between June 2016 and October 2017. In addition, in situ data from a local meteorological station highlighted the important contribution of precipitation as a trigger of the collapse. The multidirectional approach used in this study demonstrated the efficiency of applying multiple remote sensing techniques, combined with a meteorological analysis, to identify triggering factors and monitor the activity of landslides. [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 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 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 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 detailThe RESIST Project: a Study of Geohazards in the Kivu Basin Region using ground- and space borne Techniques
Libert, Ludivine ULiege; d'Oreye, Nicolas; Kervyn, François et al

Poster (2015, September)

Presentation of the goals and means of the RESIST project

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See detailSplit-Band Interferometric SAR Processing Using TanDEM-X Data
De Rauw, Dominique ULiege; Kervyn, François; d'Oreye, Nicolas et al

in ESA SP-731 (2015, March)

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. This process, named Multi Chromatic Analysis (MCA) corresponds to performing a spectral analysis of SAR images. Split-Band SAR interferometry (SBInSAR) is based on 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. In this paper, we present an SBInSAR processor and its application using TanDEM-X data over the Nyiragongo volcano. [less ▲]

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See detailMulti-Chromatic Analysis of SAR Images for Coherent Target Detection
Bovenga, Fabio; Barbier, Christian ULiege; De Rauw, Dominique ULiege et al

in Remote Sensing (2014), 6

This work investigates the possibility of performing target analysis through the Multi-Chromatic Analysis (MCA), a technique that basically explores the information content of sub-band images obtained by ... [more ▼]

This work investigates the possibility of performing target analysis through the Multi-Chromatic Analysis (MCA), a technique that basically explores the information content of sub-band images obtained by processing portions of the range spectrum of a synthetic aperture radar (SAR) image. According to the behavior of the SAR signal at the different sub-bands, MCA allows target classification. Two strategies have been experimented by processing TerraSAR-X images acquired over the Venice Lagoon, Italy: one exploiting the phase of interferometric sub-band pairs, the other using the spectral coherence derived by computing the coherence between sub-band images of a single SAR acquisition. The first approach introduces the concept of frequency-persistent scatterers (FPS), which is complementary to that of the time-persistent scatterers (PS). FPS and PS populations have been derived and analyzed to evaluate the respective characteristics and the physical nature of the targets. Spectral coherence analysis has been applied to vessel detection, according to the property that, in presence of a random distribution of surface scatterers, as for open sea surfaces, spectral coherence is expected to be proportional to sub-band intersection, while in presence of manmade structures it is preserved anyhow. First results show that spectral coherence is well preserved even for very small vessels, and can be used as a complementary information channel to constrain vessel detection in addition to classical Constant False Alarm Rate techniques based on the sole intensity channel. [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 detailApplication de la télédétection optique et RADAR pour contribuer à une gestion hydrique efficiente de la céréaliculture des périmètres irrigués au Maroc : Cas du périmètre irrigué du Tadla.
Benabdelouahab, Tarik ULiege; Balaghi, Riad ULiege; Barbier, Christian ULiege et al

Scientific conference (2013, February 06)

« l’Application de la télédétection optique et radar pour contribuer à la gestion de la céréaliculture dans les périmètres irrigués : cas du périmètre irrigué de Tadla ». Cette présentation est un résumé ... [more ▼]

« l’Application de la télédétection optique et radar pour contribuer à la gestion de la céréaliculture dans les périmètres irrigués : cas du périmètre irrigué de Tadla ». Cette présentation est un résumé de projet de thèse doctorale qui vise à contribuer à une gestion synoptique du périmètre irrigué grâce aux outils de la télédétection spatiale optique et radar combinés à la modélisation agrométéorologique. [less ▲]

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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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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 detailStrategic Research Agenda for High-Altitude Aircraft and Airship Remote Sensing Applications
Barbier, Christian ULiege; Delauré, Bavo; Lavie, Arie

in International Archives of Photogrammetry (2006), XXXVI-1/W44

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