Fabien Blarel (LEGOS-OMP, France); Denis Blumstein (CNES, France); Fernando Niño (LEGOS-OMP, France)

Spaceborne radar sensors provide global observation of continental surfaces at different frequencies, resolution, incidence angles and polarizations. Backscattering coefficients (σ0) from radar scatterometers and Synthetic Aperture Radar (SAR) images are commonly used to monitor the dynamics of key variables characterizing the continental surfaces, such as vegetation density or surface soil moisture (SSM). Spatial and temporal variations of radar altimeter (RA) backscattering coefficients (σ0) were related to the dynamics of surface properties over land and ice sheets. Over land, RA backscattering coefficients at C-band were used to detect flood in Siberia. Signatures of soil roughness and SSM changes in the deserts were identified at Ku band using ERS-1 and Topex/Poseidon data. Backscattering coefficients from Topex/Poseidon were found to be decreasing as vegetation increase in Sahel. A comprehensive comparison of radar signatures acquired over West Africa (between 0° and 25°N and 5°W - 25°E) at both C- and Ku- bands using nadir-looking altimeters (35-day orbital period ENVISAT RA-2 over 2003-2010 and 10-day orbital period Jason-2 over mid-2008-2012) that covers the major bioclimatic zones, soil and vegetation types encountered in this region was performed. A recent study also demonstrated the capability to retrieve SSM from ENVISAT RA-2 backscattering coefficients over Sahelian savannahs in the Gourma region of Mali. Preliminary results using the first of SARAL measurements at Ka-band showed the potential of Ka-band for detecting SSM changes and water even under forest canopy. SARAL data exhibit very high values (>50 dB) of backscattering coefficients (i.e., bursts) at Ka-band over land. In this study, we propose an identification of these bursts and an analysis of their cause.