ABSTRACT
Soil moisture is a key land surface state variable for its important role in regulating the energy and moisture fluxes between the atmosphere and land surface. It is an important boundary condition for the atmosphere and imposes a strong control on the water and energy exchanges between the land and atmosphere through regulating the evapotranspiration flux (Koster and Suarez, 1992). Better knowledge of soil moisture greatly contributes to our understanding of land surface processes (Albertson and Parlange, 1999; Cahill et al., 1999). Because the land surface soil moisture has a longer memory than the dynamic processes in the atmosphere, better quantification of land surface soil moisture status has the potential to improve numerical weather
3.1 Introduction .................................................................................................... 37 3.2 Estimating Soil Moisture Content from Microwave Sensors ......................... 38
3.2.1 Radiative Transfer Process from Ground to Space and Passive Remote Sensing .................................................................................. 39
3.2.2 Radar Backscatter and Active Remote Sensing.................................. 41 3.3 Satellite Missions and Microwave Sensors ..................................................... 43
3.3.1 Passive Sensors ................................................................................... 43 3.3.2 Active Sensors .................................................................................... 43
3.4 Soil Moisture Retrieval Products .................................................................... 43 3.5 Validation, Uncertainty Assessment, and Imitations of Microwave
Soil Moisture Estimates ..................................................................................46 3.6 Applications .................................................................................................... 49 3.7 Summary ........................................................................................................50 References ................................................................................................................ 51
forecasts at both short-term and seasonal scales (Koster and Suarez, 2001), especially in the warm season when land-atmosphere interactions are greatest. Operational large-scale soil moisture observational products would likely enhance the accuracy of numerical weather prediction products, hydrologic flood forecasting, agricultural drought monitoring as well as water cycle research related to climate studies. Soil moisture information is also of great value in agriculture and water resources management, especially for drought management (Sheffield and Wood, 2007; Mo, 2008).
