激光相干法测量次表层海水温度的理论与实验研究

In view of the problems of current sub-surface seawater temperature telemetry, combined with the sensing technology development status of atmospheric temperature based on Rayleigh scattering, A random laser coherent method is proposed to measure the laser Rayleigh scattering spectra in seawater so as to remote sense seawater temperature. A broadband high-speed photodetector is used to receive the random beating signal produced by the frequency stabilized local oscillator light and the random Rayleigh scattering light, and Fourier transform analysis is used to get the Rayleigh Scattering spectra, and then obtain the seawater temperature. The theoretical and experimental study involve the quasi-elastic scattering properties of Rayleigh scattering of seawater and its model description, the theory analysis and computer simulation of the random coherent process of local oscillator light and random Rayleigh scattering light, the Fourier transform analysis of the beating signal, the inversion algorithm and error analysis of seawater temperature, as well as and the modification of the Rayleigh scattering temperature sensing model. Purposes of this study are accurate descripting the Rayleigh scattering properties of seawater, establishing the Rayleigh scattering broadening spectra model, clarifying the intrinsic mechanism of seawater temperature telemetry based on Rayleigh scattering, exploring a new method as laser coherence method to measure the Rayleigh scattering spectra in order to realize the rapid measurement of sub-surface seawater temperature, make some contribution to the theoretical innovation and experimental exploration of raplidly temperature remote sensing of large area sub-surface seawater.

针对目前次表层海水温度测量技术中存在的问题，结合瑞利散射大气温度遥感技术的发展现状，提出了采用激光随机相干新方法，通过测量激光在海水中的瑞利散射光谱对海水温度进行遥感测量的研究课题。利用宽带高速光电探测器接收稳频的本振激光与随机瑞利散射光相干产生的差频信号，进行傅里叶变换分析可以快速获取瑞利散射光谱，反演海水温度。研究内容涉及海水瑞利散射的准弹性散射特性及其模型描述，连续本振激光与脉冲瑞利散射光随机相干过程的理论分析与计算机模拟，差频信号的傅里叶变换分析，海水温度反演算法和误差分析、校正算法以及瑞利散射海水温度检测模型的修正等理论和实验研究。本课题研究目的是准确描述海水瑞利散射特性，建立海水瑞利散射展宽谱模型，阐明其用于海水温度遥测的内在机理，探索一条采用激光随机相干方法测量瑞利散射光谱从而测量次表层海水温度的新途径，为实现次表层海水温度快速大面积测量的理论创新和实验探索贡献一份力量。

针对目前次表层海水温度测量技术中存在的问题，对采用相干探测测量海水瑞利散射谱的测量方法进行了理论分析和软件模拟，采用连续532nm单频激光搭建了随机相干瑞利散射温度遥感实验系统，进行实验。由于受连续单频激光峰值功率低、瑞利散射信号小的影响，产生的相干差频信号信噪比低，未能实现瑞利展宽光谱的实验测量和水温的探测。转变思路，提出了一种基于双受激布里渊散射光束相干测量海水温度的方法，可大幅度降低相干测量频率，通过理论和实验研究表明该方法是可行的。针对基于受激布里渊散射光束相干测量海水温度的方法受激光器的脉冲宽度和峰值功率限制导致频率测量精度低的问题，进一步提出了一种基于单受激布里渊散射光束相干测量海水温度的方法，降低了对激光器脉冲宽度的要求，在8ns窄脉冲条件下实现了较高精度的水温测量。研究结果为实际相干海水温度遥感系统的设计提供了有价值的参考。为了实现海水温度的高精度实时测量，通过理论和实验研究了激光波长对拉曼散射测温雷达系统水温测量精度和探测深度的影响，设计研制了基于450nm激光和532nm激光的低成本实用化的拉曼散射雷达水温遥测系统，应用时空累加数据算法有效增强了雷达系统的灵敏度和信噪比，开发了基于LabVIEW的拉曼光谱实时采集、数据处理系统，实现了水温的实时连续遥测，提出的基于频数分布的拉曼光谱滤波算法有效去除了实际测量中的干扰噪声；通过大量室内和现场实验验证了系统的温度测量精度和稳定性。