浑浊水体激光后向散射特性仿真与实验研究

由于水体的吸收和散射作用，光束能量在传播的过程中会产生衰减，激光脉冲会被展宽，制约着水下激光雷达的探测范围和探测精度。文中以浑浊水体环境下水下弱小目标探测为应用背景，建立了水下光子传播的蒙特卡洛仿真模型，模拟了不同衰减系数和散射率的水体后向散射回波信号，并对相应的水体后向散射回波信号变化趋势进行了分析。仿真结果表明：随水体衰减系数的增加，近场水体激光回波信号接收光子数逐渐增多；随水体散射率的增加，回波信号光子消亡速度逐渐降低。开展了不同浊度下的激光雷达回波信号的测试实验，实验结果表明：随水体衰减系数的增加，水体激光后向散射回波幅度逐渐增高，脉冲宽度逐渐展宽。在进行浑浊水体水下弱小目标探测时，随水体衰减系数的增加，应通过逐渐减小激光器能量或接收系统增益来增强水体回波与目标回波之间的差异，以此提高浑浊水体水下弱小目标探测的信噪比。实验验证了理论与仿真结果，为浑浊水体环境下水下弱小目标激光探测系统在不同水质下的激光能量选取、接收系统增益设计等提供理论支撑。

Simulation and experimental study on laser backscattering characteristics in turbid water

Due to the absorption and scattering of water, the beam energy will attenuate in the process of propagation, and the laser pulse will be widened, which restricts the detection range and accuracy of underwater lidar. Based on the application background of underwater weak and small target detection in turbid water environment, this paper establishes the Monte Carlo simulation model of underwater photon propagation, simulates the backscattering echo signal of water body with different attenuation coefficients and scattering rates, and analyzes the variation trend of the corresponding backscattering echo signal of water body. The simulation results show that the number of photons received by the laser echo signal of near-field water body gradually increases with the increase of attenuation coefficient of water body; With the increase of water scattering rate, the photon extinction speed of echo signal gradually decreases. The lidar echo signal test experiments under different turbidity are carried out. The experimental results show that with the increase of water attenuation coefficient, the laser backscattering echo amplitude of water gradually increases and the pulse width gradually widens. When detecting dim and small underwater targets in turbid water, with the increase of attenuation coefficient of water, the difference between water echo and target echo should be enhanced by gradually reducing laser energy or receiving system gain, so as to improve the signal-to-noise ratio of dim and small underwater targets in turbid water. The experimental results verify the theory and simulation results, and provide theoretical support for the laser energy selection and the gain design of the receiving system of the underwater weak and small target laser detection system under different water qualities in the turbid water environment.