Remote Sensing of Soil Moisture: State-of-the-Science.

Satellites (e.g., SMAP, SMOS) using passive microwave techniques, in particular at L band frequency, have shown good promise for global mapping of near-surface (0-5 cm) soil moisture at a spatial resolution of 25-40 km and temporal resolution of 2-3 days. C- and X-band soil moisture records date back to 1978 making available an invaluable data set for long-term climate research. Near-surface soil moisture is further extended to root zone (top meter) using process based models and data assimilation schemes. Validation of remotely sensed soil moisture products has been ongoing using core monitoring sites, sparse monitoring networks, intensive field campaigns, as well as multi-satellite comparison studies. To transfer empirical observations across space and time scales and to develop improved retrieval algorithms at various resolutions, several efforts are underway to associate soil moisture variability dynamics with land surface attributes in various energy and water rich environments. In this presentation we will describe the most recent scientific and technological advances in soil moisture remote sensing. We anticipate remotely sensed soil moisture will find many applications in vadose zone hydrology in the coming decades.