References of "Kirkove, Murielle"
     in
Bookmark and Share    
Full Text
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 ▲]

Detailed reference viewed: 56 (9 ULiège)
Full Text
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 ▲]

Detailed reference viewed: 47 (12 ULiège)
Full Text
Peer Reviewed
See detailIterative Phase Retrieval Assisted Off-Axis Terahertz Digital Holography
Zhao, Yuchen ULiege; Vandenrijt, Jean-François ULiege; Kirkove, Murielle ULiege et al

in Applied Optics (2019), 58(32),

In THz digital holography, the off-axis configuration is the appropriate choice when the investigated object is non-sparse and complex. The limitation of recording distance in off-axis configuration ... [more ▼]

In THz digital holography, the off-axis configuration is the appropriate choice when the investigated object is non-sparse and complex. The limitation of recording distance in off-axis configuration restricts the imaging quality. Either low resolution or spectra overlap can potentially occur. We propose an iterative phase retrieval approach to improve the quality of reconstruction results obtained from off-axis hologram. One additional capture of object wave intensity is recorded to perform iterative phase retrieval with off-axis reconstruction as the initial guess. Apodization operation can be applied to the object wave intensity capture to suppress undesired border diffraction effects. The image quality using the proposed method has been improved both from simulation and experimental verification. [less ▲]

Detailed reference viewed: 75 (18 ULiège)
Full Text
See detailThermography-inspired processing strategy applied on shearography towards nondestructive inspection of composites
Kirkove, Murielle ULiege; Zhao, Yuchen ULiege; Blain, Pascal ULiege et al

in Proceedings of SPIE: The International Society for Optical Engineering (2019, June 21), 11056

Detailed reference viewed: 62 (23 ULiège)
Full Text
See detailImaging quality and resolution enhancement by iterative phase retrieval in THz off-axis digital holography
Zhao, Yuchen ULiege; Vandenrijt, Jean-François ULiege; Kirkove, Murielle ULiege et al

in Digital Holography and Three-Dimensional Imaging 2019 (2019, May 23)

The intrinsic resolution of 2.52 THz off-axis digital holography system is known to be diffraction limited. However, in practical recording condition, reference wavefront would inevitably suffer excessive ... [more ▼]

The intrinsic resolution of 2.52 THz off-axis digital holography system is known to be diffraction limited. However, in practical recording condition, reference wavefront would inevitably suffer excessive diffraction or obstruction with large off-axis angle. Consequently, the theoretical resolution cannot be achieved, and the imaging quality is degraded. We propose a phase-retrieval-assisted solution to correct the errors caused by inaccurate reference wave. Experimental results demonstrate enhanced imaging quality and recovered lateral resolution. [less ▲]

Detailed reference viewed: 35 (10 ULiège)
Full Text
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 ▲]

Detailed reference viewed: 47 (8 ULiège)
Full Text
Peer Reviewed
See detailDetermination of vibration amplitudes from binary phase patterns obtained by phase-shifting time-averaged speckle shearing interferometry
Kirkove, Murielle ULiege; Guérit, Stéphanie; Jacques, Laurent et al

in Applied Optics (2018), 57(27), 8065-8077

Speckle shearing interferometry (shearography) is a full-field strain measurement technique that can be used in vibration analysis. In our case, we apply a method that combines the time-averaging and ... [more ▼]

Speckle shearing interferometry (shearography) is a full-field strain measurement technique that can be used in vibration analysis. In our case, we apply a method that combines the time-averaging and phase-shifting tech- niques. It produces binary phase patterns, where the phase changes are related to the zeroes of a Bessel J 0 function, typical of time-averaging. However, the contrast and resolution are better compared to traditional time-averaging. In a previous paper, we have shown that this is particularly useful in vibration testing performed under industrial conditions, because fringe patterns are noisier than in quiet laboratory environments. This paper goes a step further in proposing a processing method for estimating the vibration amplitude, for helping non-experts to identify vibration modes. Since shearography measures the spatial derivative of displacement, spatial integration is required. Prior to that, different processes like denoising, binarization, automated nodal line detection, and amplitude assignment are applied. We analyze the performance of the method on synthetic and experimental data, in the function of noise level and fringes density. Results on data acquired in an industrial environment illustrate the good performances of the proposed method. [less ▲]

Detailed reference viewed: 41 (11 ULiège)
Full Text
Peer Reviewed
See detailProcessing of binary fringe patterns obtained by phase-shifting time-averaged shearography on vibrating objects
Kirkove, Murielle ULiege; Guérit, Stéphanie; Jacques, Laurent et al

in Jaroszewicz, L. R. (Ed.) Proceedings of SPIE volume 10834, 7th International Conference on Speckle Metrology, Speckle 2018 (2018, September 07)

Shearography can be used for full-field strain measurements in the field of vibration analysis. It provides the spatial derivative of the optical phase difference of the vibration modes amplitude along ... [more ▼]

Shearography can be used for full-field strain measurements in the field of vibration analysis. It provides the spatial derivative of the optical phase difference of the vibration modes amplitude along the so-called shear direction. The shearographic setup considered here is based on the phase-shifting time-averaged technique. It can easily be applied experimentally, but its drawback is that binary phase patterns are obtained. These phase changes are related to the zeroes of a Bessel function. Retrieving the corresponding displacement maps is not straightforward. Moreover, integration of shearographic results need to be performed, and this step is sensitive to noise in the patterns. In this paper, different processing stages are described, from fringe denoising to integration of the displacement maps. The application on data acquired in industrial environment illustrates the good performances of the proposed method. [less ▲]

Detailed reference viewed: 46 (16 ULiège)
Full Text
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 ▲]

Detailed reference viewed: 94 (5 ULiège)
Full Text
See detailArtificial defects in CFRP composite structure for Thermography and Shearography nondestructive inspection
Blain, Pascal ULiege; Vandenrijt, Jean-François ULiege; Languy, Fabian ULiege et al

in Proceedings of SPIE 10449, Fifth International Conference on Optical and Photonics Engineering (2017, April)

Locating defects in CFRP composite materials is a hot topic in nondestructive inspection (NDI). Beside classical NDI technique, such as ultrasound testing (UT), contactless techniques are actively studied ... [more ▼]

Locating defects in CFRP composite materials is a hot topic in nondestructive inspection (NDI). Beside classical NDI technique, such as ultrasound testing (UT), contactless techniques are actively studied. Generally manufacturers of CFRP structure incorporate artificial defects in the bulk, with different extents and depths, in order to study the performance of a specific NDI technique to detect the defect. One of the most common defects in CFRP is delamination between two layers. This is simulated by inserting teflon sheets which, like air, acts as ultrasound blocker in UT. When such reference part is used to assess NDI performance of thermography or shearography, we only observe respectively the thermal or mechanical response of teflon with respect to external loading used with these techniques. In this work, we assess other possibilities for artificial defects in CFRP matrix. For that a CFRP structure was developed and which incorporates teflon, flat-bottom holes and delamination obtained by the pull-out method. We experimentally studied the signals and we discuss the difference between the various artificial defects methods. [less ▲]

Detailed reference viewed: 66 (23 ULiège)
Full Text
See detailChange Detection Using Interferometric and Polarimetric Signatures in Argentina
Dadamia, Danilo; Thibeault, Marc; Palomeque, Mathias et al

Scientific conference (2017, January 23)

The two-satellite SAOCOM-1A/B SAR constellation to be deployed by Argentina shall provide full-polarimetric acquisitions at L-band, the main mission driver being the generation of soil moisture maps in ... [more ▼]

The two-satellite SAOCOM-1A/B SAR constellation to be deployed by Argentina shall provide full-polarimetric acquisitions at L-band, the main mission driver being the generation of soil moisture maps in the agriculture and hydrological contexts. The two satellites shall be incorporated, together with the Italian COSMO-Skymed satellites, in an X-L band constellation (referred to as SIASGE system) for risk management. Following an offer from CONAE, ESA has initiated the development of a passive receiving micro-satellite, SAOCOM-CS, for carrying out tomographic, interferometric, and bistatic imaging. SAOCOM-CS will fly in formation with SAOCOM-1B providing unique new single-pass measurements at L-band. The present paper reports the first results from an on-going study that comes in support to both the SAOCOM and SAOCOM-CS missions. The objective of this project is to accomplish a breakthrough in the development of algorithms and associated tools for change detection in Argentina, the core domain of focus being agriculture. The processing developments carried out in this project include a study of the polarimetric signature for different targets, and a multitemporal, spatial and angular analysis of the polarimetric parameters for different L band targets. The results are then applied in non-supervised algorithms for classification of SAR images and the development of simulated SAR images. Tests data sets include airborne and spaceborne SAR images and corresponding field measurements. [less ▲]

Detailed reference viewed: 56 (11 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 117 (7 ULiège)
Full Text
Peer Reviewed
See detailEvaluation of the performance of an experimental somnolence quantification system in terms of reaction times and lapses
François, Clémentine ULiege; Wertz, Jérôme ULiege; Kirkove, Murielle ULiege et al

in Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society (2014, August)

Detailed reference viewed: 84 (35 ULiège)
Full Text
Peer Reviewed
See detailComparative evaluation of existing and new methods for correcting ocular artifacts in electroencephalographic recordings
Kirkove, Murielle ULiege; François, Clémentine ULiege; Verly, Jacques ULiege

in Signal Processing (2014), 98(C), 102-120

EEG signals are often contaminated by ocular artifacts (OAs), in particular when they are recorded for a subject that is, in principle, awake, such as in a study of drowsiness. It is generally desirable ... [more ▼]

EEG signals are often contaminated by ocular artifacts (OAs), in particular when they are recorded for a subject that is, in principle, awake, such as in a study of drowsiness. It is generally desirable to detect and/or correct these OAs before interpreting the EEG signals. We have identified 11 existing methods for dealing with OAs. Their study allowed us to create 16 new methods. We performed a comparative performance evaluation of the resulting 27 distinct methods using a common set of data and a common set of metrics. The data was recorded during a driving task of about two hours in a driving simulator. This led to a ranking of all methods, with five emerging clear winners, comprising two existing methods and three new ones. [less ▲]

Detailed reference viewed: 74 (25 ULiège)
Full Text
Peer Reviewed
See detailPerformance evaluation of methods for correcting ocular artifacts in electroencephalographic (EEG) recordings
Kirkove, Murielle ULiege; François, Clémentine ULiege; Libotte, Aurélie et al

Conference (2013, February)

The presence of ocular artifacts (OA) due to eye movements and eye blinks is a major problem for the analysis of electroencephalographic (EEG) recordings in most applications. A large variety of methods ... [more ▼]

The presence of ocular artifacts (OA) due to eye movements and eye blinks is a major problem for the analysis of electroencephalographic (EEG) recordings in most applications. A large variety of methods (algorithms) exist for detecting or/and correcting OA’s. We identified the most promising methods, implemented them, and compared their performance for correctly detecting the presence of OA’s. These methods are based on signal processing “tools” that can be classified into three categories: wavelet transform, adaptive filtering, and blind source separation. We evaluated the methods using EEG signals recorded from three healthy persons subjected to a driving task in a driving simulator. We performed a thorough comparison of the methods in terms of the usual performances measures (sensitivity, specificity, and ROC curves), using our own manual scoring of the recordings as ground truth. Our results show that methods based on adaptive filtering such as LMS and RLS appear to be the best to successfully identify OA’s in EEG recordings. [less ▲]

Detailed reference viewed: 133 (48 ULiège)
Peer Reviewed
See detailContrast and sensitivity performances of Elscint, General Electric, Siemens and SMV multi-heads cameras.
Kirkove, Murielle ULiege; Seret, Alain ULiege

in European Journal of Nuclear Medicine and Molecular Imaging (2007, October), 34(S2), 345

Detailed reference viewed: 58 (5 ULiège)