基于拉曼激光雷达的大气三相态水同步精细探测分光系统的设计与仿真分析

Design and simulation analysis of spectroscopic system for synchronous atmospheric three-phase water detection based on Raman lidar

水是惟一具有三相态的大气参数,三相态水的分布研究对认识云微物理、云降水物理以及人工影响天气过程具有重要的科学意义.在大气三相态水的拉曼激光雷达探测技术中,需首先解决三相态水的高光谱分光技术,以保证对回波信号的精细提取和高信噪比探测.考虑到水汽、液态水和固态水的拉曼光谱特性,本文首先通过理论仿真详细探讨了各拉曼通道中滤光片的选型参数对三相态水光谱重叠特性和探测信噪比的影响;并针对两者无法同时取得最优解的情况,提出了利用多目标规划问题的评价函数方法,分析获得了各通道最优的滤光片参数.结果表明,当固态水、液态水和水汽通道窄带滤光片中心波长和带宽分别为397.9 nm(3.1 nm), 403 nm (5 nm)和407.6 nm (0.6 nm)时,可获得各通道间最低的光谱重叠度值和最佳探测信噪比,从而实现了三相态水同步探测拉曼分光系统的优化设计.进一步的仿真结果表明,当激光雷达探测效率因子为1800 J·mm·min时,在有云条件下系统可获得白天3.6 km以上和晴天条件下4 km以上的三相态水有效探测,保证了利用拉曼激光雷达实现对三相态水的同步高信噪比探测,为后续大气三相态水的拉曼激光雷达同步探测和反演提供了技术和理论支持.

Water is the only atmospheric parameter with three-phase states. The study on distribution and variation in three-phase water is of great scientific significance for understanding cloud microphysics, cloud precipitation physics,and water circulation, especially in the fields of artificial weather process. In the Raman lidar detection technology of three-phase water, it is necessary to solve the problem of high-spectral spectroscopic technique to ensure fine extraction of the echo signal and the detection with high signal-to-noise ratio（SNR）. Considering the Raman spectrum characteristics of three-phase water, the influences of filter parameters in the Raman channels on the overlapping characteristics are theoretical simulated and discussed in detail, and the SNR is investigated as well. Regarding the fact that optimal solution can be obtained for neither overlapping nor SNR at the same time, an evaluation function method based on the multi-objective programming problem is proposed to analyze the optimal filter parameters. The results show that the minimum overlapping value and the higher system SNR can be obtained when the central wavelength and bandwidth of the filters are determined to be 397.9 nm and 3.1 nm, 403 nm and 5 nm, 407.6 nm and 0.6 nm in solid water, liquid water and water vapor channel, respectively, and thus the optimal design can be realized for synchronous detection Raman spectroscopic system for three-phase water. Further simulation results show that effective detection can reach above3.6 km in the daytime and over 4 km on sunny days under a system factor of 1800 J·mm·min for three-phase water Raman measurement in the daytime. Furthermore, the obtained overlapping values are applied to accurate retrieval theory for three-phase water profiles. The simulated profiles of atmospheric water vapor, liquid water and ice water indicate that the water vapor, liquid water and solid water content can be increased synchronously in the cloud layer,and their content, distribution characteristics and the corresponding error are also discussed. The above results validate the feasibility of highspectral spectroscopic technique for detecting the synchronous atmospheric three-phase water, and will provide technical and theoretical support for synchronous retrieval of three-phase water by Raman lidar.