海水布里渊散射谱特征参数测量方法研究

发布时间：2018-10-04 22:01

【摘要】：近年来,基于法布里珀罗标准具(FPE)结合增强型电耦合元件(ICCD)的布里渊激光雷达系统被广泛用来遥感海洋特性,如海水温度、声速、盐度等。在该系统中,采用ICCD记录布里渊散射信号经过FPE后形成的干涉圆环图样,然后从干涉圆环图样中提取布里渊谱特征参数如布里渊频移和半高线宽等信息,进而根据谱特征参数与海水介质特性的关系反演得到海水特性。该方法为非扫描式测量,测量耗时短,对入射光的准执行、立体角以及激光器的单稳频特性没有严格要求,能适应实际海洋遥感测量应用中复杂恶劣的环境。然而,一方面受到目前ICCD像素尺寸限制,ICCD记录的干涉谱分辨率有限;另一方面经过FPE后得到的干涉谱与入射布里渊散射频谱的相关理论不完备,没有对两者进行区分。这两个因素共同限制了该技术的测量精度,传统处理方法的散射频谱测量精度只有约几十MHz,对应约1oC的温度精度,无法满足高精度测量应用的需求。为了提高该系统的布里渊散射谱特征参数的测量精度,本文首先研究了海水布里渊散射的基础理论知识以及布里渊散射测量海水温度原理,为后续工作奠定理论基础;然后研究了FPE的工作原理以及布里渊散射光经过FPE后的干涉圆环图样形成原理,从理论上对干涉谱和入射布里渊散射频谱进行了区分;在认知到了两者区别之后,本文在总结针对干涉谱的传统处理方法的基础上,对干涉圆环图样进行预处理提高了干涉谱分辨率,并提出了新的干涉谱拟合反演模型,采用列文伯格-马夸特(L-M)算法进行最小二乘误差拟合反演,精确获取布里渊散射频谱,提高谱特征参数测量精度;针对L-M算法中参数设置问题,进行了预分析和优化设置。最后通过实验验证,证实该方法可以实现高精度谱特征参数的测量,测量精度达到MHz量级,对应海水温度测量精度提高到0.1oC,测量精度得到了显著提高。
[Abstract]:In recent years Brillouin lidar systems based on Fabry-Perot standard with (FPE) and enhanced electrically coupled element (ICCD) have been widely used for remote sensing of ocean characteristics such as sea water temperature sound velocity salinity and so on. In this system, the interference ring pattern formed by Brillouin scattering signal through FPE is recorded by ICCD, and the Brillouin spectrum characteristic parameters such as Brillouin frequency shift and half-high linewidth are extracted from the interference ring pattern. Then the characteristics of seawater are obtained by inversion of the relationship between spectral characteristic parameters and the characteristics of seawater media. This method is a non-scanning measurement, which takes a short time to measure, has no strict requirements for the quasi-execution of incident light, the stereo angle and the single frequency stability of the laser, and can adapt to the complex and harsh environment in the practical marine remote sensing application. However, on the one hand, the resolution of interference spectrum is limited by ICCD pixel size, on the other hand, the theory of interference spectrum and incident Brillouin scattering spectrum obtained by FPE is not complete, and they are not distinguished from each other. These two factors limit the measurement accuracy of this technique. The traditional method of scattering spectrum measurement has only about dozens of MHz, corresponding to the temperature accuracy of about 1oC, which can not meet the needs of high precision measurement. In order to improve the measurement accuracy of Brillouin scattering characteristic parameters, the basic theory of Brillouin scattering and the principle of Brillouin scattering measuring seawater temperature are studied in this paper. Then, the working principle of FPE and the formation principle of the interference ring pattern of Brillouin scattering light passing through FPE are studied, and the interference spectrum and the incident Brillouin scattering spectrum are distinguished theoretically. On the basis of summarizing the traditional processing methods of interference spectrum, this paper improves the resolution of interference spectrum by preprocessing the interference ring pattern, and puts forward a new inversion model of interference spectrum fitting. Levenberg-Marquardt (L-M) algorithm is used for least square error fitting inversion to obtain Brillouin scattering spectrum accurately and to improve the measurement accuracy of spectral characteristic parameters. The parameter setting problem in L-M algorithm is pre-analyzed and optimized. Finally, the experimental results show that this method can achieve high precision spectral characteristic parameter measurement. The measurement accuracy reaches MHz level, and the corresponding seawater temperature measurement precision is improved to 0.1oC, and the measurement precision is improved significantly.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P715

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