A method and system for monitoring a region of interest are presented. Incident radiation is transmitted towards the region of interest with a certain transmitting angle and with a predetermined angular intensity distribution of the incident radiation. The transmitting angle defines a plane of propagation of the incident radiation, the region of interest being located within this plane. Reflections of the incident radiation are collected with a solid angle of collection intersecting with said plane. A region of intersection presents a detecting window of a predetermined geometry containing at least a portion of the region of interest. The collected radiation coming from within the detecting window is detected, and output signals indicative thereof are generated.