Surface soil moisture estimates over an arid area of northwest China derived from passive microwave observations

7 years (2002-2008, inclusive) of surface soil moisture data were obtained during the growing season (April-October), using measurements from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E), taken at a frequency of 6.9 GHz, for an arid area in northwestern China. A unique model for estimating surface soil moisture over the study area was developed, based on the first-order radiative transfer model calculation. Taking into consideration the extremely complex topography over the study area, we presented a parameterization of surface roughness at 6.9 GHz and spatial resolution of the AMSR-E using the annual minimum Microwave Polarization Difference Index (MPDI). The estimated values of soil moisture were compared to ground observations for two representative sites in 2002-2004. The results indicated that there was also agreement between them, with high correlation coefficients (R=0.649, 0.604) and RMSE (3.5, 5.4%).