SMAP (Soil Moisture Active Passive) Handbook: Mapping Soil Moisture and Freeze/Thaw from Space
Soil moisture is a primary state variable of hydrology and the water cycle over land. In diverse Earth and environmental science disciplines, this state variable is either an initial condition or a boundary condition of relevant hydrologic models. Applications such as weather forecasting, skillful modeling and forecast of climate variability and change, agricultural productivity, water resources management, drought prediction, flood area mapping, and ecosystem health monitoring all require information on the status of soil moisture.
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