To the accuracy of small slope approximation of Kirchhoff technique [remote sensing]

For remote sensing data interpretation, it is necessary to take the influence of the surface roughness on the brightness temperature of the surface radio thermal self-radiation into account. Of practical use is to obtain analytical equations for the brightness temperature. In this work, within the scope of Kirchhoff technique (within the geometrical optics), accuracy of the analytical equations for the surface brightness temperature, which were obtained by the authors in their previous works in the small slope approximation, is investigated. These analytical equations are numerically compared to those for Kirchhoff technique for arbitrary slopes, for which shadowings are taken into account, It is shown that the analytical equations can be used for the incident angle values far from the nadir. This fact can be of use when interpreting actual surface remote sensing data, as it can significantly simplify calculations of the brightness temperature expected.