Radiance variation relative to the solar-inclination over a gaussian model of relief

A relief is modeled by a centered sample continuous gaussian process, with stationary increments, X = {Xt, 0 <= t <= T}, 0 < T < [infinity]. On this relief, the sun shines at an inclination 0 <= [theta] <= [pi]/2 and sheds shadow zones on the relief. What is observed is the mean quadratic average variation of the shadow process, Then, knowing this quadratic variation, that is to say, [short parallel]L[theta], X[var epsilon](x) - L[theta], X[var epsilon](y)[short parallel]2, for small values of x - y, we answer the following question: what is the gaussian process taking place of for the model of relief? This is carried out by getting a two-sided inequality of [short parallel]L[theta], X[var epsilon](x) - L[theta], X[var epsilon](y)[short parallel]2, expressed in terms of [short parallel]X(x) - X(y)[short parallel]2.