Evaluation of the Soil Water Index and Surface Soil Moisture on the Loess Plateau

Abstract：In this paper,the capability of the European Remote Sensing Satellite（ERS） scatterometer-derived soil water index（SWI） and surface soil moisture（SSM） data which are retrieved by a change detection method,developed at the Institute of Photogrammetry and Remote Sensing（IPF）,Vienna University of Technology（TU-Wien） to disclose soil moisture and precipitation distribution on Loess Plateau is investigated with the help of GIS,remote sensing and correlation analysis.Monthly averaged SWI/SSM data for the years 1992—2000 are analyzed to evaluate the use of the SWI/SSM as an index to monitor soil moisture on Loess Plateau and to investigate whether it can reflects general precipitation distribution characteristics in this area or not.Monthly averaged in situ relative soil moisture and monthly precipitation data from Chinese meteorological gauge stations are employed to perform comparisons with SWI/SSM on point and regional scales.The result is that in different land use,soil texture and topography conditions SWI/SSM correlate well with precipitation and in situ relative soil moisture,most of them reach significant level,they have same change tendency,SWI and precipitation have similar spatial distribution characteristics.Among the seven stations,there is a good correlation between precipitation and soil water content（SWI and in situ relative soil moisture）,especially for first 10 cm layer,the correlation between precipitation and SWI is better than that of precipitation and in situ moisture.The results show that SWI/SSM can relative accurately disclose soil moisture variation and spatial distribution characteristic on the Loess Plateau.Furthermore,the freely available 20-yr（1992—2011） time series SWI/SSM data are thus a valuable tool to overcome the scarcity of in situ soil moisture observation,which are usually not available on regional scale.