Stephane Meric

Investigations on OFDM Signal for Range Ambiguity Suppression in SAR Configuration

This paper presents an opportunity to cancel range ambiguities in synthetic aperture radar (SAR) configuration. One of the limitations of SAR systems is the range ambiguity phenomenon that appears with long delayed echoes. The reflected signal corresponding to one pulse is detected when the radar has already transmitted the next pulse. Thus, this signal is considered as an echo from the next pulse. This paper investigates the opportunity of coding the transmitted pulses using an orthogonal frequency-division multiplexing pulse. The results show that coded-OFDM signals outperform conventional chirp signal and make it possible to relax constraints placed upon the pulse repetition frequency.

Matching stereoscopic SAR images for radargrammetric applications

The aim of this paper is to present our studies about extraction of 3D information from radar images. Several radargrammetric methods allow DEM (digital elevation model) generation from SAR images and we take a special interest to stereoscopic method. The main idea is to match image stereo pairs, to create a disparity map from one image to the other and to compute elevation thanks to the incidences angles.

Mapping dynamic wetland processes with a one year RADARSAT-2 quad pol time-series

Remotely sensed data are widely used to identify, delineate and characterize wetlands. Optical data provide interesting information on land-use and land cover but are limited to cloud-free periods and to a description of the top layer of the vegetation strata because penetration depth is very small. For these reasons, it is not possible to precisely inventory wetland vegetation and agricultural practices, as well as water cycles and water levels in these areas with passive remote sensing techniques. The objective of this article is to evaluate fully polarimetric RADARSAT-2 time-series datasets to determine the water cycle dynamics, in order to delineate precisely potential, effective and efficient wetlands. To that end, the development and validation of a supervised PolSAR segmentation including multi-temporal analysis of wetland evolution, and the investigation of polarimetric decomposition methods for quantitative physical parameter inversion algorithms are presented. The proposed methodology is based on the segmentation of a polarimetric descriptor, the Shannon Entropy, which has been shown to be a very sensitive parameter to the temporal variability of flooded areas. The results have been validated using soil moisture measurements in the field and a LiDAR image. They show that it is possible to produce detailed water feature maps useful for delineating water tables as well as water-saturated areas, and for monitoring water area dynamics. These products provide useful information to identify and delineate wetlands in order to support conservation and management in these ecosystems across large areas.

Spaceborne fully polarimetric time-series datasets for land cover analysis

The objective of this paper is to make a review of the current status of the project entitled Evaluation of RADARSAT-2 quad-pol data for functional assessment of wetlands (Id6842), developed in the frame of the CSA-ESA SOAR-EU (Science and operational applications research for Europe) program by a consortium comprising I.E.T.R at the University of Rennes 1 and COSTEL-LETG at the University of Haute-Bretagne. The main objective of this project concerns in evaluating fully polarimetric RADARSAT-2 time-series datasets to delineate precisely effective and potential wetlands, map detailed vegetation distribution, identify agricultural practices and determine water cycle and waterlevels.

On the use of fully polarimetric RADARSAT-2 time-series datasets for delineating and monitoring the seasonal dynamics of wetland ecosystem

The project entitled Evaluation of RADARSAT-2 quad-pol data for functional assessment of wetlands (Id6842), developed in the framework of the CSA-ESA SOAR-EU (Science and operational applications research for Europe) aims to contribute to the application development in demonstrating the exploitation of fully polarimetric time-series datasets for the functional assessment of wetlands. The objective of this paper is to address the issue of evaluating fully polarimetric RADARSAT-2 time-series datasets to determine the water cycle dynamics, in order to delineate precisely potential, effective and efficient wetlands.

Synthesis of Sparse Planar Arrays for Passive Imaging Systems Based on Switch Submatrix

In order to reduce the cost of imaging systems, the use of a switch matrix instead of the standard multichannel schema is considered to be a good solution. However, the design of a switch matrix for imaging applications is a complex task, particularly for a 2-D array because it depends mainly on the array topology, the number of channels, and the required performance. In this letter, a switch submatrix approach for a passive imaging system is presented and discussed. The goal is to reduce the complexity and the cost of the system architecture while maintaining its high performance. An optimization method that is able to yield optimal sparse arrays with a very low redundancy and an optimized switching process is then proposed. Numerical results confirm the efficiency of the proposed method. A good tradeoff between cost, performance, and system complexity is also reported.

Using Polynomial Wigner–Ville Distribution for Velocity Estimation in Remote Toll Applications

This letter presents the use of polynomial Wigner-Ville distribution (PWVD) for accurate velocity estimation as used in remote road traffic management applications. In such applications based on inverse synthetic aperture radar, velocity estimation is central to obtain a suitable level of performance of the signal processing. Moreover, the precision of this velocity estimation is crucial in order to achieve the best detection and estimation of the gauge of the vehicles through the use of radar images. Hence, the PWVD is applied as an instantaneous frequency estimator used in this traffic surveillance application.

FMCW RADAR SYSTEM FOR TRANSPONDER IDENTIFICATION

In this paper, we deal with a frequency modulated continuous wave (FMCW) radar used for localizing and tracking targets by frequency evaluation of the received radar beat signal. The radar system achieved with a primary radar (reader) and a secondary radar (transponder) is addressed as super high frequency (SHF) radio frequency identification (RFID). Consequently, considering the transponder as an active target, we achieve an identification application thanks to the shift frequency induced by the transponder. Moreover, the impact of the non-linearity behavior of this transponder on the localization performance is investigated, and a solution is proposed for cancelling non-linear effects.

A 2D synthetic aperture radiometry demonstrator by switching strategy at X band

The broad topic of the presented paper consists in the research on novel methods in the field of microwave imaging, in particular the so-called passive microwave / millimeter-wave imaging, which is also referred to radiometric imaging. This study focuses on proximity range applications such as concealed objects detection, human body screening, etc. The aim is to design a low cost and compact fully electronic passive imaging system suitable for short-range 2D imaging applications, and study the necessary devices for the implementation of a complete demonstrator. In this study, a new approach based on the use of a switch sub-matrix strategy has been adapted into a complete antenna system at X band. The main objective of this prototype is to validate this approach experimentally. Image quality is examined by using the interferometric aperture synthesis technique and G-matrix calibration imaging algorithms. The spatial resolution is measured by using the emission from noise source and is compared with theory.

Polarimetric multi-angular Radarsat-2 data sensitivity to surface parameters

The objective of this study is to evaluate the potential of C-band polarimetric multi-angular Radarsat-2 datasets to characterize soil moisture and surface roughness over bare agricultural fields. The polarimetric parameters derived from single angular and dual angular SAR data are examined to analyze the polarimetric sensitivities to bare surfaces. In the case of single angular analysis, the results show that smooth surfaces can be separated from medium rough as well as rough surfaces. Polarimetric parameters SRalpha1, ρhhvv have potentials to characterize soil moisture. In the case of dual angular analysis, the backscattering coefficient differences between two incidence angles Δσ in HH and VV polarization depend negatively on surface roughness and positively on soil moisture.