Soil moisture retrieval from L-band SAR data and hydrologic modelling

Soil moisture content is a parameter of major importance for land applications at both watershed and regional scale such as hydrology and agriculture. In the past, a vast number of experimental and theoretical studies relating radar measurements to soil and vegetation parameters have been conducted. Such studies have widely demonstrated the sensitivity of Synthetic Aperture Radar (SAR) measurements to soil moisture content. The inverse problem of retrieving soil parameters from the observed radar response of the surface has also been widely investigated, although, no retrieval algorithm is yet operational. An important part of the limitations to monitor superficial soil moisture is due to the disturbing effect of surface roughness and vegetation layer modulating the radar sensitivity to the soil moisture content thus rendering intricate the retrieval problem. A promising approach consists of using multi-temporal SAR data and a priori information on surface parameters to improve the robustness and the accuracy of retrieval algorithms [e.g. Mattia et al., TGARS, vol. 44, n. 4, April 2006]. To gather a priori information on soil moisture content different approaches, ranging from networks of ground stations to estimates derived from spaceborne microwave radiometer or from hydrologic modelling, can be exploited.