Estimation of Canopy Attenuation for Active/Passive Microwave Soil Moisture Retrieval Algorithms

This paper discusses the importance of the proper characterization of scattering and attenuation in trees needed for accurate retrieval of soil moisture in the presence of trees. Emphasis is placed on determining an accurate estimation of the propagation properties of a vegetation canopy using the complex frequency correlation function (FCF). A new technique for determining the canopy attenuation that uses the measured stepped frequency radar backscatter response is proposed. It makes use of the details found in a transient solution where the canopy (volume scattering) and the tree-ground (double interaction) effects appear at different times. The proposed technique is based on separating the backscattering sources within a forest canopy in the time response. The technique has been used with L band data collected over deciduous trees to verify that the algorithm results match the simulated data.