SIR-C/X-SAR as a bridge to soil moisture estimation using current and future operational satellite radars

The Shuttle Imaging Radar experiments in 1994 (SIR-C/X-SAR) involved simultaneous data acquisition at a variety of frequencies and polarizations that included those of all existing and near future satellite SAR systems. As part of SIR-C/X-SAR a soil moisture experiment was conducted in the Little Washita watershed located in Oklahoma. Hydrologic conditions during the April mission started from a mostly wet soil condition with no additional rain for the duration of the mission. A data set of georegistered SIR-C and X-SAR data and ground observations has been prepared for distribution. Daily changes in incidence angle were normalized using published results for various land cover types. These normalized data were then related to soil moisture for satellite configurations representative of ERS-1 and 2, Radarsat, JERS-1, and other planned missions. Initial results show that for rangeland regions the empirical angular correction performs well and that some single frequency-polarization combinations can be used for estimating soil moisture if additional land cover/vegetation factors are considered