Polarization Detection Technology of Underwater Targets for Airborne Lidar

摘要

The fundamental principle of the airborne green-blue lidar for the underwater target detection is that a 532nm pulse laser beam is transmitted from an aircraft and reflected by the underwater targets, and then the airborne laser receiving system receives the echo signals. Besides the useful target signal, the echo signals also contain a lot of background noises, and the main one is the seawater backscattering noise. Therefore, restraining the effect of the noise on the signal light is important to enhance the detection depth and reduce the false alarm rate. Since the end of 1960s, many experiments on the underwater detection techniques of the airborne laser have been finished in US and Australian, especially for the laser propagation characteristics through the different water quality. Some French researchers made a depolarization experiment on the submerged targets by using the circularly polarized light and linearly polarized light with the 532nm wavelength in 1990. In 1987, extensive experiments were carried out in the former Soviet Union on the polarization receiving characteristics of echo signals after the laser produced by lidar through the atmosphere. The results showed that the target contrast could be enhanced significantly by using polarization receiving, and in the case of a smaller receiving FOV (field of view), the contrast effect was much better. This paper makes some theoretical and experimental research on the scattering depolarization characteristics of airborne laser through the seawater.