Complex Interferometric Coherence Loci for the Rvog and Ovog Models with a Dominant Double-bounce Scattering in a Single-transmit Acquisition Mode

Mathematical expressions for the interferometric coherence of homogeneous-volume-over-ground models (RVoG and OVoG) for the case of dominant specular scattering and considering a single-tx interferometer are derived. The analysis of the positions of the coherences on the complex plane, as a function of the polarization channel, yields important differences for the single-tx and the alternate-tx acquisition modes when the ground return is dominated by the double-bounce contributions. An additional volume decorrelation term appears when the interferometer is operated in a single-tx mode. This feature makes more difficult the parameter inversion from PolInSAR observables, since the topographic phase is not represented anymore by the crossing between the line formed by the coherences and the unit circumference. The effect of this bistatic volume decorrelation is even more noticeable for the cross-polar channel in the oriented volume case, since the phase of the coherence with an infinite ground-to-volume ratio does not correspond to the topographic phase, as observed for the copolar channels. Additionally, a preliminary study of the influence of the bistatic volume decorrelation as a function of the bistatic angle has been carried out.