Estimation of watershed soil moisture index from ERS/SAR data

The aim of this article is to show that a watershed hydrological index coul d be derived from ERS/SAR measurements. Indeed, it is well known that, over bare soil, the SAR signal is a function of the geometric and dielectric su rface properties. The problem to estimate soil moisture is to free from the effects of the space and time fluctuations of soil roughness and from the vegetation cover attenuation and scattering. The methodology presented here is based on the selection of land cover types or "targets," for which the SAR signal is mainly sensitive to soil water content variations, and for wh ich the vegetation and the roughness effects (in SAR signal) can be estimat ed and removed if needed. This method has been validated over an agricultur al watershed in France. We show that the accuracy of the retrieved soil moi sture is +/-0.04-0.05 cm(3)/cm(3), except during May and June, when vegetat ion cover is too dense to get reliable soil information. (C) Elsevier Scien ce Inc., 2000.