RELATION BETWEEN ERS-1 SYNTHETIC-APERTURE RADAR DATA AND MEASUREMENTSOF SURFACE-ROUGHNESS AND MOISTURE-CONTENT OF ROCKY SOILS IN A SEMIARID RANGELAND

Surface roughness and soil moisture content control the distribution o f rainfall into runoff, evapotranspiration, and infiltration. Satellit e radar data have the potential to provide spatial and multitemporal e stimates of these variables, depending upon the sensor configuration a nd field condition. The relation between the European Remote Sensing S atellite (ERS-1) synthetic aperture radar (SAR) data and measurements of surface roughness and moisture content of rocky soils in a semiarid rangeland in southeast Arizona was analyzed in this study. A dry and a wet season C band SAR image were acquired and corrected for topograp hic effects. Field soil roughness and moisture content data were obtai ned from 47 sampling sites. An intensive soil moisture sampling campai gn was also conducted at three sites to determine the number of sample s necessary to estimate soil moisture content with 10% accuracy. Dry a nd wet season SAR data were found to be correlated (r(2) = 0.80 and 0. 59, respectively) with root-mean-square (RMS) height measurements, whi le SAR data from the wet season image were poorly correlated with soil moisture. The results indicated that C band SAR data are promising fo r estimation of surface roughness in semiarid rangelands. However, the y are less promising for soil moisture estimation, unless the effects of soil roughness and vegetation are removed. The acquisition of an ad equate number of soil moisture samples to obtain representative soil m oisture measurements is also a key issue in the validation of soil moi sture retrieval from SAR data. In the study area, at least 17 samples per hectare were needed to obtain soil moisture estimates with 10% acc uracy.