Comparison of ESTAR and SSM/I derived surface soil moisture

Southern Great Plains 1997 (SGP97) is an EOS interdisciplinary science hydrology experiment with a goal of mapping surface soil moisture over an 10,000 km/sup 2/ area at 800 m resolution with an airborne L band radiometer on a daily basis for a month. It took place from June 18 to July 16, 1997 in Oklahoma. The areal coverage ranged from the Little Washita River watershed in the south to the Department of Energy's Central Facility for the Atmospheric Radiation Measurement (ARM) program near the Kansas border in the north. Extensive ground measurements of soil moisture were collected at the Little Washita watershed, the Central Facility area, and USDA's El Reno watershed west of Oklahoma City. This experiment offers a unique data set for examining the applicability of microwave soil moisture retrieval algorithms at spatial and temporal scales more typical of satellite systems. In addition to the L-band Electronically Scanned Thinned Array Radiometer (ESTAR), the core sensor for the SGP97, brightness temperature data are also available from a spaceborne radiometer, the Special Sensor Microwave/Imager (SSM/I) aboard the DMSP satellite series. Although the SSM/I is not optimal for soil moisture retrieval, it can under some conditions provide information. Rigorous analyses over land by SSM/I data have been difficult due to the lack of good validation data sets. With the data collected for the SGP97, the objective of this paper is to compare the surface soil moisture estimated from the SSM/I data with those retrieved from the ESTAR data using the same retrieval algorithm.