Microwave Measurement of Soil Moisture and Freeze/Thaw Timeline

Hydros will provide the first global views of the land hydrosphere state (soil moisture and surface freeze/thaw), which exerts the primary control on land-atmosphere exchanges of water, energy, and carbon over most of the Earth. Hydros builds upon the knowledge and experience base of microwave remote sensing of soil moisture and freeze/thaw which began with small point-scale studies using tower-mounted radiometers in the late 1960s and early 1970s and truck- and aircraft-mounted microwave instruments during the late 1970s and 1980s.

These early studies were aimed at verification of theory, determination of the most sensitive instrument characteristics, and development of accurate microwave retrieval algorithms. By the 1990s, comprehensive aircraft field campaigns were being conducted to explore spatial and temporal concepts of soil moisture retrieval at the 100s of meters scale and to carry out large scale regional mapping and integrated hydrologic research at the kilometer scale.

The 1990s also saw the first use of spaceborne SARs and scatterometers to map freeze/thaw transitions across landscape and regional scales. This work is continuing in the 2000s, with additional focus on the synergism between active and passive microwave remote sensing and on integrated surface modeling.

With the advent of L band missions such as SMOS and Hydros in the 2007-2010 timeframe, more accurate global mapping of soil moisture and freeze/thaw at higher spatial resolution will be possible for the first time, leading to significant advances in numerical weather prediction, climate and process modeling, and hydrologic and agricultural applications.