THE INFLUENCE OF POLARIZATION ON CANOPY TRANSMISSION PROPERTIES AT 6.6 GHZ AND IMPLICATIONS FOR LARGE-SCALE SOIL-MOISTURE MONITORING IN SEMIARID ENVIRONMENTS

Nimbus/SMMR 6.6 GHz data were used together with an extensive data base of surface moisture to study the influence of polarization on radiative transfer characteristics of savannah vegetation in south-eastern Botswana. Ratios of vertical and horizontal polarization optical depths and ratios of albedos were found to be almost constant throughout a three-year period. This conclusion led to a new approach to eliminate the vegetation components in the remotely sensed brightness temperatures, which is important for soil moisture monitoring from space. Using the same data set, this dual-polarization approach was compared with an earlier described synergistic approach, in which NDVI was used to eliminate the vegetation effects. The root mean square error between ground based soil moisture and satellite estimated surface soil moisture was reduced to 1.2% by volume from 5% by volume using the dual polarization approach.