海洋激光雷达多次散射回波信号建模与分析

海洋激光雷达是实现上层海水3维探测的重要工具,激光在海水中的传输伴随着复杂的多次散射效应,建立准确的海洋激光雷达多次散射回波信号模型有助于实现海水光学特性的高精度反演。本文介绍了仿真海洋激光雷达多次散射信号的解析模型、半解析MC(Monte Carlo)仿真方法和传统MC仿真方法,定量对比分析了不同工作条件下3种模型的仿真结果,讨论了工作高度、接收视场角、水质和水体分层等因素对仿真结果的影响。研究表明:3种模型具有高度一致的仿真结果,但在计算效率方面,解析模型优于半解析MC法,半解析MC法优于传统MC法。解析模型优异的计算效率和可靠的计算精度使其在海洋激光雷达辐射传递机理及应用的研究中具有显著优势。

Modeling and analysis of oceanic lidar returns with multiple scattering

Oceanic lidar is a powerful tool that can detect the depth-resolved profiles of the upper ocean water. Seawater optical properties are usually retrieved according to the single scattering lidar equation. However, the accuracy of the simplified equation cannot be guaranteed because of the multiple light scattering in the ocean, which calls for an accurate and effective lidar return model. The accuracy of Monte Carlo (MC) simulation gains recognition because of few assumptions. However, MC simulation is limited by its low efficiency. The computation cost in the analytical model decreases. This phenomenon has not been verified in the oceanic lidar. Therefore, evaluating the accuracy of the analytical model is essential. The principles of the analytical model, conventional MC simulation, and semi-analytic MC simulation were introduced. The analytical model generally depended on the quasi-small-angle approximation. Under such approximation, the radiative transfer equation was solved in the Fourier space using the small angle approximation, which reduced the complexity of the calculation. The conventional MC simulation is based on the purely stochastic construction of an ensemble of photon trajectories through the medium of interest. The semi-analytic approach is used to reduce the statistical error of the conventional MC simulation by combining stochastic and analytic techniques. The effects of operating parameters, such as the height, field of view, water types, and distribution of phytoplankton layers, on the lidar signals were analyzed and compared. The results showed that the analytical model agrees well with the MC simulation in the homogenous and stratified water. However, in terms of the calculation efficiency, the semi-analytic MC is faster than the conventional MC, and the analytical model is faster than semi-analytic MC. As a result, high accuracy and remarkable efficiency make the analytical model superior in the simulation of the oceanic lidar return. Methods for simulating oceanic lidar signals, including the analytical model, conventional MC simulation, and semi-analytic MC simulation, were introduced in this paper. Simulations based on these methods were performed under different operating parameters and demonstrated the high accuracy and remarkable efficiency of the analytical model. These advantages make the analytical model superior in the simulation of the oceanic lidar return. The physical mechanism of laser propagation in the water and retrieval of optical parameters based on oceanic lidar will be the prospective objectives based on the method and result in this work.