The ensemble of passive microwave remote sensing observations collected during the recent Southern Great Plains 97 Hydrology (SGP97) experiment represents one of the best opportunities to date to examine the effects of sub-pixel heterogeneity at a variety of spatial scales and wavelengths.
Recently published work suggests that L-band observations would not be sensitive to the spatial distribution of vegetation within a pixel up to average column densities of several kg/m2 (grasses and certain crops), while higher frequency observations would be sensitive. This is an issue of general relevance to microwave remote sensing of land areas, and of particular interest in the context of near-future spaceborne soil moisture sensing missions.
SGP97 was conducted in Oklahoma from mid-June through mid-July, 1997. Regular observations were made during this period from ground-based, aircraft, and spaceborne microwave sensors. The ground-based observations consist of hourly L, S, and C band measurements from the SLMR instrument plus half-hourly measurements at the 19, 37, and 85 GHz SSM/I frequencies from the TMRS2 instrument. Both SLMR and TMRS2 were located at the ARM/CART Central Facility, and both have spatial resolutions measured in meters. Aircraft measurements consist primarily of L-band imagery from the ESTAR instrument, and possibly C-band data. The daily ESTAR imagery covers a 50 x 280 km strip with 800-meter resolution including the Central Facility in the north. The satellite observations include overflights by SSM/I instruments several times per day. The spatial resolution of the SSM/I data varies from 15 km to about 50 km.
Given the data availability timeframe, the results will be primarily empirical in nature. Model-based studies would be expected to provide more detailed analyses at a later date.