The impact of vegetation growth on DInSAR coherence regions and estimated deformations

The polarization diversity of the phase in differential interferometry causes ambiguities in the estimation of displacements: it might be related to complex dynamic processes such as vegetation growth. As the properties and possible origins besides noise-like influences of such diversity over changing vegetation canopies are virtually unknown, we propose to investigate them empirically using an L band data set covering one growing season over different agricultural crops. The polarimetric coherence regions (i.e. the shape and relation to biomass) over wheat, barley and, to a lesser extent, rape suggest the presence of birefringence within the canopy, which can yield phase differences between HH and VV channels exceeding 0.5π. The remaining fields (maize and sugar beet) - while also showing such a dependence on polarization - cannot be explained by birefringence. Irrespective of the origin of this dependence, its presence and magnitude indicate the importance of vegetation effects in differential interferometry, with potentially deleterious influences on the estimation of deformations.