Abstract
The technique of using microwave radar to remotely observe surface soil moisture is based on the principle that the backscattering coefficient θ0 depends on the dielectric constant ε which is strongly related to the volumetric soil moisture content θ. In this study, both the ε vs. θ relationships and the σ0vs. θ relationships in three types of soil (alluvial soil, diluvial soil and volcanic ash soil) which are found in agricultural land were investigated experimentally. The results obtained were as follows:1) The ε (measured with the TDR system) vs. θ relationships in the three tested soils were significantly different from the common relationships derived by Topp et al. (1980). The peculiar dielectric properties in the three tested soils resulted from the well-developed aggregate structures and low dry bulk densities.2) There were large differences found in dry soil conditions between the σ0 vs. θ (within the top 2cm layer) relationships in the three tested soils and the soil examined by Bruckler and Witono (1989). These differences were considered to result mainly from the differences of the dielectric properties in these soils.
