Scatterers characterisation in radar imaging using joint time–frequency analysis and polarimetric coherent decompositions

Abstract

Classical radar imaging generally considers targets as set of isotropic independent sources with a constant response in the measured frequency band. Nevertheless, new radar capabilities, in terms of signal bandwidth and angular excursion, may challenge this bright point model. Studies based on multidimensional time-frequency (TF) analysis, describing the angular and frequency behaviour of a scene's reflectivity, showed that some scatterers may have anisotropic and dispersive responses. Polarisation diversity is an interesting additional source of information in radar imaging, and provides indicators closely linked to some geometric and electromagnetic properties of the observed objects. In this study, a fully polarimetric TF analysis is proposed for radar imaging (SAR, ISAR) that characterises the anisotropic and dispersive behaviour of the polarimetric response of deterministic targets. This method is based on the hyper-image concept, which describes the response of scatterers as a function of the observation angle, the emitted frequency and polarimetric canonical behaviours. Polarimetric hyper-images point out that non-stationary behaviours can be related to physical properties of the target (geometrical shape, relative orientation) and allow a better understanding of the scattering mechanisms. This polarimetric hyper-image representation is then used to detect non-stationary scatterers and to classify their behaviour.

Design of New Wavelet Packets Adapted to High-Resolution SAR Images With an Application to Target Detection

“…When a target is illuminated using a large bandwidth and a large range of angles, it is more reasonable to assume that its response is dependent of the wave vector. Recent studies of the spectral and angular behaviour of the scatterers have shown the variation of the scatterers' response for several angles of illumination and several frequencies [2], [45]. Figure 2 presents an ONERA SAR image in X-band.…”

Multidimensional very high resolution SAR interferometry for monitoring energetic structures

“…It characterizes an "extended image" relative to the spatial repartition I( r). Such images can be built using the Short Time Fourier transform (STFT) and are called hyper-images [7]. Since the STFT is an atomic decomposition, the phase of hyper-image is preserved and it can be used for interferometric processing.…”

Multivariate change detection on high resolution monovariate SAR image using linear time-frequency analysis

“…We assume that the scatterers present in the scene will respond to an electromagnetic wave in all directions and in all frequencies. This hypothesis is reasonable for low-resolution SAR systems, but it was shown ( [7], [8], [9], [10], [11], [12]) that for recent high-resolution SAR imagery, it does no longer apply. The scatterers can have a peculiar signature in angle and frequency domains.…”