LARGE-AREA MAPPING OF SOIL-MOISTURE USING THE ESTAR PASSIVE MICROWAVERADIOMETER IN WASHITA92

Washita'92 was a large-scale study of remote sensing and hydrology con ducted on the Little Washita watershed in southwest Oklahoma. Data col lection during the experiment included passive microwave observations using an L-band electronically scanned thinned array radiometer (ESTAR ) and surface soil moisture observations at sites distributed over the area. Data were collected on 8 days over a 9-day period in June 1992. The watershed was saturated with a great deal of standing water at th e outset of the study. During the experiment there was no rainfall and surface soil moisture observations exhibited a drydown pattern over t he period. Significant variations in the level and rate of change in s urface soil moisture were noted over areas dominated by different soil textures. ESTAR data were processed to produce brightness temperature maps of a 740 sq, km, area on each of the 8 days. These data exhibite d significant spatial and temporal patterns. Spatial patterns were cle arly associated with soil textures and temporal patterns with drainage and evaporative processes. Relationships between the ground-sampled s oil moisture and the brightness temperatures were consistent with prev ious results. Spatial averaging of both variables was analyzed to stud y scaling of soil moisture over a mixed landscape. Results of these st udies showed that a strong correlation is retained at these scales, su ggesting that mapping surface moisture for large footprints may provid e important information for regional studies.