Comparison between SLMR and ESTAR soil moisture retrieval in SGP97

No current satellite measurement system can provide soil moisture data from space, and previous process studies and algorithm development activities for microwave remote sensing of soil moisture have been limited in their spatial extent. To remedy this situation and build a strong foundation for a soil moisture space mission, an EOS interdisciplinary science hydrology experiment called Southern Great Plains '97 (SGP97) was conducted by NASA and USDA in Oklahoma during June-July, 1997 in order to acquire data at spatial and temporal scales more typical of satellite systems. A core activity of SGP97 involved mapping surface soil moisture with the ESTAR (Electronically Scanned Thinned Array Radiometer) airborne L band microwave radiometer on a daily basis for a month over an 11,000 km/sup 2/ area at 800 m resolution. To provide continuous 24-hour microwave brightness temperature measurements over two representative surface covers (winter wheat and grazed pasture) to complement the once-a-day ESTAR data, the two-frequency truck-mounted passive microwave SLMR (S and L Microwave Radiometer) system was also deployed to the Department of Energy's ARM/CART Central Facility site in the northern part of the SGP97 test region for the month-long experiment. The availability of both truck-based and aircraft L band brightness temperature measurements over the same site in SGP97 offers a unique opportunity to investigate the effects of pixel heterogeneity and scaling on soil moisture retrieval. The detailed diurnal time series data available from the SLMR system also permits validation and refinement of coupled energy/water balance models at the point scale before these models are extrapolated to the entire SGP97 test area.