激光波长对拉曼散射水温遥感系统测温精度及探测深度的影响

Effects of laser wavelength on both water temperature measurement precision and detection depth of Raman scattering lidar system

机载激光拉曼散射雷达技术可以快速获取次表层海水温度的三维分布,具有重要的实用价值和经济价值.首先,从理论上分析了水的伸缩振动拉曼谱峰值位置和半高全宽与激发波长之间的对应关系,发现随着激发波长的增大,拉曼峰逐渐向长波方向移动,且拉曼光谱半高全宽显著增大.然后,实验测量了不同温度下450 nm激光和532 nm激光激发的水的拉曼光谱,对比验证了上述理论分析结果.并采用单高斯峰拟合法分析了两组拉曼光谱,拟合出高斯峰峰值位置与温度之间的关系,分析了激发波长对温度测量精度的影响.研究发现,采用较长波长的激发光可以提高拉曼光谱的测量精度,从而改善测温精度.最后,建立了拉曼散射雷达方程,分析了拉曼散射系数与激光波长之间的关系,研究了激光波长对雷达系统探测深度的影响.结果表明,激光波长对雷达系统探测深度有很大的影响,采用480 nm以下波长的激光时雷达系统探测深度较大,而采用长波段激光时雷达系统探测深度会大幅降低.实际系统设计中选取激光光源时需要综合考虑上述两方面的影响.

Airborne Raman scattering laser lidar technology can measure the three-dimensional （3D） distribution of subsurface seawater temperature rapidly, and it has important social and economic values. In this paper, firstly, the relationship between Raman stretching vibration spectrum peak position and excitation wavelength, and the relationship between the full width half maximum （FWHM） of Raman stretching vibration spectrum and excitation wavelength are analyzed theoretically. The results show that as the excitation wavelength increases, Raman scattering peak gradually shifts toward longer wavelength and the Raman spectrum FWHM increases noticeably. Secondly, to verify the theoretical results, the Raman spectra at different water temperatures excited by 450 nm and 532 nm lasers are measured experimentally, and the fitting analyses of them by single Gauss peak fitting method are made, the relationship between Gauss peak wavelength and temperature is obtained, and the effect of laser wavelength on the temperature measurement precision is analyzed. It is found that larger excitation wavelength can increase Raman spectrum measurement accuracy, thereby improving the temperature measurement precision. Finally, the Raman scattering lidar equation is established, the Raman scattering coefficients and attenuation coefficients of different wavelength lasers are analyzed, and the corresponding effects of laser wavelength on the lidar system detection depth are studied. Results show that the lidar system detection depth is greatly influenced by the laser wavelength, lidar system with laser wavelength below 480 nm has a good detection ability, and large wavelength laser greatly reduces lidar system detection depth. The effects of laser wavelength on both temperature measurement precision and detection depth should be considered in the desigin of Raman scattering lidar system.