This paper concerns the analysis of NLOS (Non Line Of Sight) illumination areas in an urban canyon. An algorithm is first described to determine these areas illuminated by multipath mechanisms. Smooth vertical walls are supposed to allow only specular bounces, whereas on the ground, several types of mechanisms may occur. We focus here on backscattering and specular reflection mechanisms on an horizontal surface that can help for target detection. This algorithm is then applied to all canyon components of a city district, to investigate statistically the occurrence of these different mechanisms in NLOS areas.