Specular multipath from rough correlated surfaces

The problem of specular reflection from rough correlated surfaces is stated, analyzed and evaluated from analysis of digitized topographic maps. Explicit expressions for some models of the surface's correlation functions are presented in closed formulas and in graphical forms. It is shown that ignoring the correlation may cause an underestimation of the specular multipath. Digitized topographic maps are used to derive the correlation functions of some geographic regions. The results derived from digitized topographic maps show that neither the exponential nor the Gaussian correlation models are generally correct. As a result, the modified specular reflection coefficient, that takes into account the correlation of the surface, is higher with respect to the case when it is assumed that the surface is uncorrelated. The analysis shows that over sea this effect is "felt" only in extreme conditions, i.e. very rough seas. However, overland surfaces, usually, this effect is an important factor in the reflection mechanism.