Under the condition of passive imaging measurement under natural light illumination, the imaging system's ability of imaging measurement and accurate tracking of distant targets is limited due to the influence of various background radiation. Using laser active illumination to illuminate distant, small and dark targets or their parts can reduce the impact of background radiation, and improve the system's accurate tracking and clear imaging ability for distant, small and dark targets. The working principle of laser active lighting monitoring system is basically the same as that of LiDAR. By adjusting the focusing state (divergence Angle) of the transmitting laser beam, the whole target or the key feature part of the target is illuminated to meet the detection requirements of the receiving system, and the purpose of imaging and accurate tracking of the target is realized. The laser and echo signals are transmitted in the atmospheric path, and the atmospheric background radiation, transmittance, scattering and absorption, as well as turbulence will affect the active illumination imaging.
