The TropiSAR campaign was conducted in French Guiana in the summer 2009 in the framework of the Phase A studies pertaining to the BIOMASS mission, one of the three for Earth Explorer candidates. Its main objectives were the evaluation of P-Band radar imaging over tropical forests for biomass and forest height estimation. Over two main forest sites, Paracou and Nouragues, a temporal decorrelation analysis is done in order to evaluate the performance of the PolInSAR technique in a single-satellite configuration. The interferometric coherence is observed to stay high after 22 days over the Paracou site, while presenting larger decorrelation over the Nouragues area, a more rugged area.