Retrieving surface soil moisture and vegetation optical depth from satellite microwave observations

Soil moisture is a key component of the water and energy balance of the Earth's surface, and as such, is important to many Earth science disciplines. Soil moisture has been identified as a parameter of significant potential for improving the accuracy of large-scale land surface-atmosphere interaction models. Because of high spatial variability, accurate estimates of surface soil moisture are often difficult to make by conventional ground measuring techniques, especially at large spatial scales. Since satellite remote sensing observations are already a spatially averaged value, they are ideally suited for measuring many land surface parameters such as soil moisture. Passive microwave remote sensing presents significant potential for providing regular spatially representative estimates of surface soil moisture at global scales. But, while the optimum wavelength for soil moisture sensing is in the L-band (1.4 GHz or /spl lambda/ = 21 cm), such a sensor has yet to be deployed operationally. However, new and improved microwave retrieval techniques that maximize the information that can be obtained from less optimum sensors, such as C-band and even X-band, are being developed. Progress from one such study is presented, along with preliminary results from several validation studies. It is currently planned to develop a 20+ year retrospective global database of surface soil moisture, to be made available through the Goddard Space Flight Center Distributed Active Archive Center (DAAC).