3. Active imaging principles

The main advantage of a lidar imager over a conventional optical system is its ability to increase range by separating stray light backscattered by the medium from that reflected by the target. To achieve this, it is necessary to be able to mark the light coming from the emitter so as to obtain a discrimination criterion for the backscattered light. Three obvious types of marking can be envisaged, leading to the three classical principles of imaging in diffusing or reverberant (volume) media.

• Angular and spatial marking: this requires the use of very fine, directional angular reception and transmission fields, and joint scanning of the transmitter and receiver.