Volume and double-bounce decorrelation effects in the OVoG model for Single-Tx PolInSAR

The formulation of the complex interferometric coherence for the oriented volume over ground model (OVoG) has been recently proposed for the case of dominant double-bounce mechanism from the ground when the interferometer is operated in single-transmit (bistatic) mode. This paper analyzes the two contributions to the total coherence function: the volume and the double-bounce terms. The study is performed by observing the model predictions of the coherence loci for several agricultural crop scenarios and with system parameters corresponding to the TanDEM-X mission. For low vegetation depths (up to 1 m) neither of the two contributions is negligible when the ground-to- volume ratio is low. However, when the backscattering returns from ground and vegetation are similar, i.e. ground-to-volume ratios around 0 dB, the volume decorrelation terms does not affect the coherence so much. As predicted by theory, higher vegetation layers yield an increase of the influence of the volume term and more differences between polarimetric channels.