复杂的水体环境，特别是水中微粒的吸收和散射作用，使得水下激光雷达测距系统的接收信号中存在大量的后向散射杂波。随着距离的增大，目标回波会逐渐淹没在杂波中，而副载波调制技术可以有效地提升目标对比度，实现水下激光雷达的测距增程。首先建立了光子在海水中传输的蒙特卡洛仿真模型，然后研究了结合激光雷达优势和微波雷达优势的副载波调制技术，给出了伪随机序列作为副载波时发射、接收和相关处理的详细步骤，最后对四种不同类型的副载波(方波、锯齿波、正弦波和伪随机序列波)在不同的水质和发射脉冲宽度的情况下进行了仿真研究。结果表明：伪随机序列对于目标对比度的提升方面性能最好。

The complex water environment, especially the absorption and scattering of particles in the water, causes a large number of backscattered clutter at the receiver of the underwater lidar ranging system. As the distance increases, the target echo will gradually drown in clutter. The modulation technology can effectively improve the contrast of the target and achieve the range extension of underwater lidar. A Monte Carlo simulation model of photon transmission in seawater was firstly established, and then the modulation technology which combining the advantages of lidar and microwave radar was studied. Then the detailed steps of transmitting, receiving and related processing was given when a pseudo-random sequence was used as a sub-carrier. Finally, four different types of sub-carriers(square wave, sawtooth wave, sine wave, and pseudo-random sequence wave) were used for simulation studies with the different water qualities and emission pulse widths. The results show that the pseudo-random sequence has the best performance in improving the contrast of the target.