Remote Sensing of Soil Moisture

Microwave sensors are probably the best soil moisture sensors, considering the strong physical relationship between the microwave response and soil moisture and the capability of microwaves to penetrate clouds, precipitation, and herbaceous vegetation. The principle advantage of active microwave sensors is that high spatial resolution can be obtained even at satellite altitudes.

Microwave sensors can provide estimates of soil moisture only in surface layers up to 10 cm thick. This depth is too shallow, compared to the 1-2 m root zone of many field crops in the tropics. Using the water content in the top 10 cm of the surface layer, the moisture content can be calculated within acceptable limits and with minimum error when the surface soil moisture estimation is made just before dawn.

Some investigations are under way at the National Remote Sensing Agency, Space Application Centre, and elsewhere to evaluate ERS- ISAR data for soil moisture estimates in the surface layers.

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