Satellite remote sensing of surface soil moisture

Soil is arguably the Earth’s most valuable nonrenewable resource and undoubtedly the most biologically diverse part of the biosphere. Roughly half of a soil’s volume is composed of mineral and organic content, while the other half consists of pores. Soil moisture (or water) content (SMC) refers to the amount of water in these pores and generally refers to the water contained in the unsaturated soil zone (e.g., Hillel 1998). SMC is affected by the soil texture (determines water holding capacity), topography (affects runoff and infiltration), land cover (influences evapotranspiration), and climate (precipitation, wind, humidity, and solar illumination), and, as a result, SMC is highly variable both in space and time. Although soil moisture comprises only a tiny percentage (~0.001%) of the total global water budget, its importance and influence in the hydrological cycle cannot be understated. It is a key parameter in the exchange of mass and energy at the land surface–atmosphere CONTENTS