Papers by Virginie Kubica
2017 Progress in Electromagnetics Research Symposium - Fall (PIERS - FALL), 2017
Spaceborne Synthetic Aperture Radar (SAR) systems usually operate over land in complex scanning m... more Spaceborne Synthetic Aperture Radar (SAR) systems usually operate over land in complex scanning modes such as ScanSAR or TOPSAR that can achieve wide swath coverage in a single pass of the satellite at the cost of degraded cross-range resolution. This work demonstrates the feasibility to produce bistatic radar images using a SAR satellite as emitter of opportunity and a stationary ground-based receiver with a 5-fold increase in cross-range resolution in TOPSAR mode. A Maximum A Posteriori-based image reconstruction method is validated using real measurements from the European Space Agency's satellite Sentinel-1A.
Burst mode SAR’s such as ScanSAR or TOPSAR can achieve wide sw ath coverage in a single pass of t... more Burst mode SAR’s such as ScanSAR or TOPSAR can achieve wide sw ath coverage in a single pass of the satellite at the cost of degraded cross-range resolution. In the bista tic configuration using a SAR satellite as illuminator of opp rtunity and a ground-based stationary receiver close to the imaged a r a, this coarse cross-range resolution can be improved in s ome favourable geometries by exploiting the sidelobe emission of the beams illuminating the adjacent sub-swaths. This pa per compares the oustanding performance that can be achieved in Sca SAR and TOPSAR mode thanks to a bistatic geometry.
IEEE Transactions on Aerospace and Electronic Systems, 2016
Wide-swath SAR imaging modes such as ScanSAR or TOPSAR share the synthetic aperture length betwee... more Wide-swath SAR imaging modes such as ScanSAR or TOPSAR share the synthetic aperture length between beam positions. This leads to a degraded along-track resolution compared to the conventional Stripmap mode. We show that this degraded resolution can be enhanced in the case of a bistatic configuration by exploiting the sidelobe emissions of the elevation beams illuminating the adjacent sub-swaths. If the SNR of the backscattered signals is sufficient, the performance of the Stripmap mode can even be restored. This concept becomes particularly useful when spaceborne illuminators of opportunity are considered. Indeed, the imaging mode of spaceborne SAR instruments is most often a wide-swath mode. Making it possible to exploit those modes to produce images with high azimuthal resolution dramatically increases the number of useful images that can be produced using emitters of opportunity. Signals from any radar satellite in the receiving band of the receiver can be used, thus further decreasing the revisit time of the area of interest. This paper proposes a cross-range resolution-enhancement method which provides an enhanced cross-range resolution compared to the one obtained by the classical burst-mode SAR processing. This method is experimentally validated using measurements acquired in a space-ground bistatic configuration.
The ASAR instrument of ENVISAT can operate in Image Mode (stripmap-like mode) and in ScanSAR mode... more The ASAR instrument of ENVISAT can operate in Image Mode (stripmap-like mode) and in ScanSAR mode (burst mode) in which five sub-swaths are used to image large swaths at the expense of azimuth resolution. The poor azimuth resolution of the ScanSAR mode in monostatic configuration can be enhanced in the case of a bistatic configuration with a receiver close to the imaged area by using the sidelobe emissions of the beams illuminating the adjacent sub-swaths in addition to the mainlobe emissions of the beam illuminating the considered sub-swath. In this paper, we describe the exploitation of the low azimuth resolution ScanSAR modes of the ASAR instrument and assess how the azimuth resolution can be improved from the nominal azimuth resolution based on real data acquired by a ground-based receiver.
For non-cooperative bistatic SAR, one of the major issue is the direct path interference. This si... more For non-cooperative bistatic SAR, one of the major issue is the direct path interference. This signal will also enter the receiver and seriously impact the SAR imaging. The image synthesis is based on the direct application of the matched filter. Imaging in the immediate surrounding of the receiver will be impaired by the range and azimuth sidelobes of the strong direct path signal caused by the conventional matched-filterbased SAR processing. In this paper, we present two methods to mitigate the range and azimuth sidelobes of the strong direct path signal: adaptive digital nullsteering and apodization of the matched filter. These methods are first evaluated on simulated signals. Next, field experiments using the European Space Agency's ENVISAT satellite as transmitter of opportunity will validate this processing.
2011 IEEE RadarCon (RADAR), 2011
One of the main challenges in opportunistic bistatic SAR imaging is the synchronisation of the re... more One of the main challenges in opportunistic bistatic SAR imaging is the synchronisation of the receiver with the transmitter of opportunity. By adaptive spatial beamforming, we can retrieve the reference signal needed to perform the synchronisation in SAR imaging. This processing also attenuates the direct path interference. In this paper, a four-element patch array antenna is considered. In addition, this phased-array can be used to reject interferences coming from external sources. The calibration of the receiver is of utmost importance considering on the one hand the significant mutual coupling between the antenna elements and on the other hand the differences in phase and gain between the reception chains. This paper discusses two calibration strategies and compares their performance on experimental data.
2006 IEEE Conference on Radar
Unlike classical bistatic radars, passive radars make use of illuminators of opportunity to detec... more Unlike classical bistatic radars, passive radars make use of illuminators of opportunity to detect targets and to estimate target parameters. One existing radio transmission suitable for passive radar operation is the Global System for Mobile Communication (GSM). For non-cooperative bistatic configurations, one of the major difficulties is the estimation of the reference signal which is required to perform detection. This reference signal, a priori unknown, can be extracted from the signal received at the antenna array provided the direction of arrival of the direct path signal is known. Conventional matched-filter based Doppler filtering offers the possibility of placing the target and interferences in a domain where they can be separated based on Doppler shift. However, slow moving targets residing near mainbeam clutter in the range-Doppler diagram, remain difficult to detect. Internal Clutter Motion (ICM) exacerbates this issue by spreading the clutter signal power in Doppler frequency. In this paper, we first present a method to estimate autonomously the direction of the illuminating GSM base station from measurements obtained with a two-element antenna array. We passively detect the azimuth of the transmitter without a priori knowledge of the environment. Spatial processing is then employed to attenuate the direct path signal and mitigate its influence on the target detection process. We then propose two methods able to cope with clutter echoes with non zero-Doppler components. We first propose an extension of a CLEAN-like algorithm. We also propose to extend adaptive matched filters to noise-like signals. The adapted matched filter can be used to suppress strictly static clutter but also clutter affected by ICM. These methods are validated by using actual clutter measurements obtained from a passive radar using a GSM base station as illuminator of opportunity.
IET International Conference on Radar Systems (Radar 2012), 2012
The ScanSAR mode allows imaging of a swath much wider than range ambiguity limits would normally ... more The ScanSAR mode allows imaging of a swath much wider than range ambiguity limits would normally allow but at the cost of degraded cross-range resolution. This degraded cross-range resolution in monostatic configuration can be enhanced in the case of a bistatic configuration with a receiver close to the imaged area by exploiting the sidelobe emissions of the beams illuminating the adjacent subswaths. In this paper, we will assess the feasibility of enhancing the cross-range resolution in ScanSAR modes of spaceborne transmitters and evaluate the impact on the revisit time. A preliminary analysis of the performance of the method on the novel ScanSAR mode, TOPSAR, is provided.
2013 International Conference on Radar, 2013
ABSTRACT Opportunistic SAR interferometry using a groundbased receiver and a spaceborne transmitt... more ABSTRACT Opportunistic SAR interferometry using a groundbased receiver and a spaceborne transmitter has previously been addressed. However, the analysis is limited to the conventional Stripmap mode of such radar satellites. The occurrence of satellite passes in Stripmap high-resolution mode is however not as frequent as passes in ScanSAR mode, hence the motivation to exploit ScanSAR mode illuminations by opportunistic receiver. In ScanSAR mode imaging, a burst-mode resolution enhancement method has been developed to enhance the cross-range resolution performance by exploiting the sidelobe emissions of the beams illuminating the adjacent sub-swaths. In this paper, the impact of this method on the interferometric performance is evaluated in the novel application of bistatic interferometry using cross-range resolution-enhanced burst-mode images.
2011 IEEE RadarCon (RADAR), 2011
SAR imaging has been historically performed using monostatic radar configurations where the trans... more SAR imaging has been historically performed using monostatic radar configurations where the transmitter and receiver shared the same location. Bistatic SAR is certainly not new. Cooperative bistatic SAR has been conducted either air-air, airspace and space-space [1]. Non-cooperative space-ground bistatic SAR as the one presented in this paper or in [2,3] present the advantages of being relatively cheap and able achieve a high revisit time by combining several satellites such as Envisat, ERS-2 or RADARSAT-2. From a tactical point, these systems are difficult to detect as they are passive. The synchronization between the transmitter and the receiver is crucial in bistatic SAR systems. This is usually done physically, by having one antenna pointing towards the transmitter and another towards the scene. A particularity of the system described in this paper is that the receive antenna consists in a phased array and that phased array is used to separate the direct-path signal from the echo signal. The spatial processing is described in a companion paper [4] while this paper concentrates on a description of the system, an analysis of the interferences present and present initial results.
2006 IEEE Conference on Radar
In this paper, we examine the feasibility of applying Space-Time Adaptive Processing (STAP) to bi... more In this paper, we examine the feasibility of applying Space-Time Adaptive Processing (STAP) to bistatic passive radars using illuminators of opportunity. The transmitters considered are GSM base stations and are non-cooperative. Although STAP has been extensively applied to signals from pulse-Doppler radars, it was never applied to arbitrary signals arising from illuminators of opportunity. We show that by computing the appropriate mixing product, we essentially convert the signal of opportunity to a pulse-Doppler like signal, hence making the application of STAP to arbitrary signals straightforward. We finally confirm these theoretical results by using real measurements.
2015 IEEE Radar Conference (RadarCon), 2015
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Papers by Virginie Kubica