Measuring soil moisture change with vegetation cover using passive and active microwave data

Abstract

Two basic microwave approaches are used to measure soil moisture, one is passive which is based on radiometry and the other is active and uses radar. Both approaches utilize the large contrast between the dielectric constant of dry soil and water. A total backscattering amount for a vegetated surface include volume, surface, and surface-volume interaction scattering terms. The backscattering model here is based on without surface-volume interaction scattering terms. In attempt to use active microwave remote sensors in estimation of soil moisture, two major problems, effects of surface roughness and vegetation cover, are faced. For a given sensor, we assume the roughness under the condition of no change during data acquisitions. The main problem for retrieval of surface dielectric properties is separate the volume scattering item from total backscattering. With the time-serial soil moisture map from L band passive microwave radiometry, the Electronically Scanned Thinned Array Radiometer (ESTAR) at Southern Great Plains 1997 (SGP97), we calculated the surface reflectivity with 800 m resolution. The volume scattering items at 800 m resolution can be derived using multi-temporal resample calibration Radarsat SAR and surface reflectivity data. Weighting the ratio of NDVI at different resolution from NOAA/AVHRR and TM, the surface reflectivity change with 50 m resolution can be estimated according to the total backscattering and volume scattering, then soil moisture change be mapped at 50 m resolution.