A summary of experimental results to assess the contribution of SAR for mapping vegetation biomass and soil moisture

This paper is an overview of the most recent results obtained by Italian groups involved in the spaceborne imaging radar-C,X-band synthetic aperture radar (SIR-C/X-SAR) hydrological experiment, by using multi-frequency and multi-polarization synthetic aperture radar (SAR) data measured by JPL/AIRSAR, SIR-C, EMISAR, ERS-1, and JERS-1 sensors. The sensitivity of backscattering coefficients to some geophysical parameters that play a significant role in hydrological processes, such as vegetation biomass, soil moisture, and surface roughness, is discussed. Experimental results show that P band appears to be suitable for the monitoring of forest biomass, whereas L band is mainly sensitive to the biomass of wide-leaf crops and C band to narrow-leaf crops. Moreover, the L-band sensor gives the highest contribution in estimating soil moisture and surface roughness. The sensitivity of backscatter to soil moisture and surface roughness for individual agricultural fields is rather low, since both parameters affect the radar signal. However, by observing data collected at different dates and averaged over a relatively wide agricultural area, the correlation with soil moisture becomes considerable, since the effects of spatial roughness variations are smoothed. Retrievals of both soil moisture and surface roughness were performed using a semi-empirical model.