THE EFFECT OF SOIL TEXTURE IN SOIL MOISTURE RETRIEVAL FOR SPECULAR SCATTERING AT C-BAND

The objective of this paper is to analyze the behavior of specular scattering for different soil texture fields at various soil moisture (m(v)) and analyze the data to retrieve the soil moisture with minimizing the effect of the soil texture. To study the soil texture effect on specular scattering 10 different soil fields were prepared on the basis of change in soil constituents (i.e., percentage of sand, silt and clay) and experiments were performed in both like polarizations (i.e., H H-polarization and V V-polarization) at various incidence angles (i.e., varying incidence angle from 25 degrees to 70 degrees in step of 5 degrees). Angular response of specular scattering coefficients (sigma degrees(hh) in H H-polarization and sigma degrees(vv) in V V-polarization) were analyzed for different soil texture fields with varying soil moisture content whereas the surface roughness condition for all the observations were kept constant. The changes in specular scattering coefficient values were observed with the change in soil texture fields with moisture for both like polarizations. Further, copolarization ratio (P = sigma degrees(hh)/sigma degrees(vv)) study was performed and it was observed that the dependency of copolarization ratio for change in soil texture field at constant soil moisture is less prominent whereas the value of copolarization ratio is varying with variation of moisture content. This emphasizes that copolarization ratio may be minimizing the effect of soil texture while observing the soil moisture on specular direction. Regression analysis is carried out to select the best suitable incidence angle for observing the moisture and texture at C-band in specular direction and 60 degrees incidence angle was found the best suitable incidence angle. An empirical relationship between P and m(v) was developed for the retrieval of m(v) and the obtained relationship gives a good agreement with observed m(v). In addition, m(v) was also retrieved through the Kirchhoff Approximation (SA) and a comparison was made with the retrieved results of empirical relationship. The empirical relationship outperformed the SA.