Abstract
A theoretical model is developed to describe the interferometric coherency between pairs of SAR images of rough soil surfaces. The model is derived using a dyadic form for surface reflectivity in the Kirchhoff approximation. This permits the combination of Kirchhoff theory and spotlight synthetic aperture radar (SAR) image formation theory. The resulting model is used to describe the interferometric coherency between pairs of SAR images of rough soil surfaces. The theoretical model is applied to SAR images formed before and after surface changes observed by a repeat-pass SAR system. The change in surface associated with a tyre track following vehicle passage is modelled and SAR coherency estimates are obtained. Predicted coherency distributions for both the change and no-change scenarios are used to estimate receiver operator curves for the detection of the changes using a high-resolution, X-band SAR system.
Highlights
Coherent change detection (CCD) using synthetic aperture radar (SAR) images from repeated apertures is an interferometric SAR technique and an increasingly important and rapidly developing area of research [1, 2, 3]
CCD techniques may be used to detect scene disturbances that occur between repeated SAR observations, which would otherwise remain undetected by incoherent change detection techniques
We demonstrate the utility of the theoretical model by performing numerical calculations designed to predict the performance of a very-highresolution SAR system capable of generating 0.15 m resolution spotlight SAR imagery
Summary
Coherent change detection (CCD) using synthetic aperture radar (SAR) images from repeated apertures is an interferometric SAR technique and an increasingly important and rapidly developing area of research [1, 2, 3]. We report a theoretical approach designed to model the detection of changes in soil surfaces The theory incorporates both a physical model for surface scattering (Kirchhoff theory, see, e.g., [5, 6, 7]) and a model for spotlight SAR signal processing [8, 9]. Surface reflectivity and the received signal We consider spotlight SAR images formed using repeated transmission of a radar pulse described by p(t ) = P(ω) exp(−iωt )dω. In repeat-pass SAR CCD, a pair of images is formed and on each occasion an observation is made of the reflectivity function: changes to the scene result in changes to this function upon which the coherency between images will depend. Given a suitable expression for the reflectivity density F(ω, s, u), (5) is in a form suitable for considering in the polar format algorithm (PFA) [8, 9]
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