The retrieval of soil moisture from satellite data is a challenging problem due to influences of other surface variables such as vegetation and surface roughness on the signal. For a successful retrieval of soil moisture, remote sensing techniques should on the one hand exhibit a high sensitivity to soil moisture and on the other hand minimize instrument noise and the influence of other surface variables on the measured signal.
Techniques for soil moisture retrievals can first be ordered into active and passive sensoring. Active instruments, such as the ERS-scatterometer, send out short pulses towards the Earth’s surface and measure the reflected pulse energy. The reflectivity of soil increases strongly with increasing soil moisture content, due to changing dielectric properties. Passive measurements, such as measurements from AMSR-E, are sensitive to soil moisture, because soil moisture influences the emissivity or the color of a soil.
A range of remotely sensed soil moisture products will be used to calibrate the drought monitoring system.
Some examples of AMSR-E based soil moisture analysis are shown below.
Timeseries AMSR-E 2002-2006
Mean soil moisture 2002-2006
