Abstract: The paper regards rain media as a discrete random system. By estimating the linearity of the system combining the system identification measure with the radio wave propagation theory, th system model is found. Then, the formula for calculating the equivalent complex refraction constant of rain media is deduced. Attenuation induced by rain is prediceted with the equivalent complex refraction constant. The attenuation predicted is nearly consistent with that calculated by the formula recomended in ITU-R and measured results, which testifies that the method used in that paper is effective. It is also helpful for other discrete media.

Key words: rain medium, equivalent complex refraction constant, system identification