Validation of AMSR-E Soil Moisture Products in Xilinhot Grassland

Soil moisture is a primary product of Advanced Microwave Scanning Radiometer for EOS (AMSR-E) which onboard Aqua satellite. AMSR-E soil moisture product provides us global soil moisture dataset from 2002 to present. It is known to all that validation is a big problem in the use of satellite remote sensing soil moisture product. The instantaneous field of view (IFOV) of different channel of AMSR-E ranges from 10 km to 50 km. For the lower frequency which is more sensitive to soil moisture, IFOV is larger. This means that a single point of AMSR-E soil moisture product contain average soil moisture of hundreds of km2 land surface. The traditional soil moisture measurement only gives us a single point soil moisture measurement result which is not equal to large area soil moisture. In this paper, we present an experiment to validate the soil moisture product of AMSR-E. The experiment was carried out from July 15, 2008 to September 30, 2008. 9. The location of the experiment is in Xilinhot grassland, Neimeng province, China. During the former period, we put 9 soil moisture and temperature measurement systems (ECH2O) in an area of about 3kmx3km. We selected this area because it's a very typical area in the Xilinhot grassland, which contain most land cover types and terrain types in the grassland. For each point, 5 layers of soil moisture and temperature were measured by ECH2O. The 5 layers are 2cm, 5cm, 10cm, 20cm and 50cm respectively. Considering the penetration depth of AMSR-E, 2cm measurements were used to do the validation. The location of the 9 ECH2O is very dispersive and the elevations of them are very different. Measurement result shows that the main factor that affects the soil moisture distribution is elevation. In grassland, soil moisture in higher place is always smaller than that of lower place. Which means a single soil moisture measurement is not suit for the soil moisture used purpose. Precipitation measurement was also done in this area during the experiment period. Result shows that the precipitation is more effective to the top layers soil moisture than the bottom layers. In our sites, only 2cm and 5cm layers are affected by the precipitation. Other layer didn't change much during the whole period. The average soil moisture measurement result in this area during the experiment is 11.8cm3/cm3, while the soil moisture product of AMSR-E in this area shows that the average soil moisture during this period is 13.3cm3/cm3. The RMSE of them is 3.7cm3/cm3. Result show that AMSR-E soil moisture product has a good accuracy in the grassland of north China.