Using two different methods, we study the radiative properties of rough surfaces, such as the bidirectional or the hemispheric directional reflectivity. The first method, which we call exact, is the integral method (MI). It is based on the electromagnetic theory and Green's theorem to describe the system through a system of equations for the field and its normal derivative (sources) at the surface. The method is computation expensive, requiring the inversion of possibly large complex matrices. The second method (MIR), which we will use and for which we extend the validity to include transverse polarization, reformulates the integral method to solve it by an iterative approach. It has the advantage that its first iteration corresponds to the Kirchoff approximation (AK). The following (higher order) terms bring corrections to AK, while reducing notably the computation load. Our main purpose is to study the stability of the MIR and to find the limits of its validity when compared with the (exact) MI. Our numerical results were carried out for perfectly conducting or dielectric surfaces with sinusoidal roughness for two polarizations, transverse electric and transverse magnetic. [Journal translation]

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