The Airborne Laser Radar Underwater Target Detection Technology

As the more widely use of lidar for underwater detection, the system detection performance has become the focus. Because of the influence of the backscatter to the system performance, how to inhibit the incoherent backscatter clutter and improve target contrast become especially important.We know the incoherent backscatter clutter coming from the independent scatterers which is random distributed, backscattering signals show low-frequency characteristics as to random scattering. However, the signals reflected from underwater target can keep all the frequency characteristics. Therefore, frequency filtering can be used to modulated Lidar on optical carrier technology for inhibiting the incoherent backscatter clutter.In order to optimize the design of the modulated-pulse lidar system, the relation between system parameters and the performance are investigated, and the principle of system parameter design is introduced. System parameters such as range of modulating frequency, modulation index, and bandwidth of filter are included. Besides, a conclusion that the modulated-pulse lidar system is suitable for water exploration in ordinary seawater condition is made based on study of the relation between environment and system performance. Then, by using the PMT variable gain control technology, the target echo contrast is incresad.The modulated-pulse lidar system has reduced backscattering signals and enhanced the target contrast over 35dB in the shallow water in computer simulation, which shows that this system has better detection effect than ordinary algorithms in shallow water with common water quality parameters. The simulation result shows that the frequency filtering method can also be applied to the system design for target identify in other channels with serious backscattering and multi-scattering.