The Dependence of the Soil Microwave Attenuation on Frequency and Water Content in Different Types of Vegetation: an Empirical Model

A layer of vegetation above the surface of the soil absorbs the microwave radiation emitted by the soil and some objects under the vegetation canopy. This paper explores the microwave propagation process within the vegetation layer and evaluates the respective attenuation coefficients. For this purpose, an experimental laboratory test bench is constructed which is based on the special rectangular camera-waveguide with the transmission and reception of broadband antennas. This allows the study of the dependence of the attenuation coefficient on the 0.8–10 GHz frequency range and the water content in different types of vegetation. Evaluations of attenuation coefficients are achieved on a wide range of frequencies for deciduous and coniferous forests, which separate the branches and trunks as canopy fragments. These experimental results are important because they can fulfill the requirement for verification and validation of existing theoretical models that describe the attenuation effect of microwave propagation in vegetation canopy. In addition, the development of a simple empirical model based on the results obtained can give a brief indication of their importance.