Baseline Decorrelation in Bistatic Interferometric SAR Systems Over Bare Soil Surfaces

In the context of bistatic synthetic aperture radar (SAR) imaging, SAR interferometry is an appealing application due to the capability of retrieving accurate topographic information or surface deformations at fractions of wavelength. Within this framework, we present a new physical-based approach to evaluate the correlation between a pair of bistatic SAR acquisitions over a bare soil surface and in a very general imaging geometry, which includes two transmitters and two receivers. Some specific configurations of practical interest for proposed bistatic spaceborne SAR missions, for example, SESAME and PLATiNO-1 (PLT-1), namely coplanar and along-track bistatic geometries, are analyzed as well. The proposed methodology makes use of electromagnetic scattering models suited to random rough surfaces, namely the Kirchhoff approximation (KA) and the first-order small-slope approximation (SSA1), under which analytical formulations of the correlation between the received electromagnetic fields are derived. It is found that in the coplanar imaging geometry, a unitary correlation coefficient can be obtained with nonnull orthogonal baselines. Closed-form expressions of the critical baseline are derived as well. The proposed approach can be applied to such scenarios where single surface scattering is the dominant mechanism, such as bare soil surfaces or scarcely to moderately vegetated areas.