SOIL MOISTURE ESTIMATION BY PASSIVE MICROWAVE IMAGER FOCUSING ON RADIATION TRANSFER IN VEGETATION LAYER

Abstract

The purpose of this study is to investigate radiation transfer in vegetation layer and apply it to soil moisture estimation by passive microwave imager in global scale. A radiation transfer scheme with multiple parameters for leaf, stem, and branch is used. Sensitivity analysis shows that not only LAI (Leaf Area Index) but SAI (Stem Area Index) has strong influence on PD (Poralization Difference of brightness temperatures) and FD (Frequency Difference of brightness temperature). Among several different estimation algorithms, an algorithm which calculates soil moisture by PD with temporal variable LAI and spatial distributed SAI can give the most realistic seasonal variation of surface soil moisture. In this algorithm, spatial distributed SAI is derived from annual minimum FD.