1 IntroductionUnlike other sensors that passively sense radiation fromtargets illuminated by the Sun, microwave remote sensinginstruments can function day and night and, at somewavelengths, they will not be interfered significantly byatmospheric conditions (e.g. clouds). Microwave remotesensing signals are sensitive to the surface roughness, theinternal structure, and the complex dielectric constant ofthe sensing objective, i.e., they can provide information onsubsurface structure and volume c…