Coherence loci for a homogeneous volume over a double-bounce ground return

The formulation of the polarimetric interferometric coherences derived by simple homogeneous-volume-over-ground models is revisited for the case of ground returns dominated by the double-bounce terms. The differences between single-transmit (single-tx) and alternate-transmit modes of the interferometer are analyzed by inspecting the positions of the coherences on the complex plane. An additional volume-decorrelation term appears when the interferometer is operated in a single-tx mode, which adds complexity in the potential inversion of the model parameters. This effect is even more noticeable for the cross-polar channels in the oriented 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.