【作者】 林宏；

【导师】 董天临； 马泳；

【作者基本信息】 华中科技大学 ， 电磁场与微波技术， 2007， 博士

【摘要】 海洋悬浮粒子的光学散射特性不仅直接影响激光在海水中的传输特性,而且是海洋环境光学监测的重要理论基础。当一束光射入海水中时,经过光与海水的相互作用,会发生弹性散射和非弹性散射。弹性散射光没有发生频移变化,但是散射特性与入射光的波长、海水的属性以及海水中悬浮粒子的大小、密度等有关。在海水中引发光弹性散射的散射元主要是海水水分子和海洋悬浮粒子等。弹性散射主要包括瑞利散射、米氏散射和无选择性散射三类,其中海水中水分子主要引起的是瑞利散射,而海洋悬浮粒子主要引起的是米氏散射。通过研究海洋悬浮粒子的米氏散射特性,可以得到海水中各种悬浮粒子的大小、密度等信息。光与海水产生的另一类散射是非弹性散射,这类散射存在散射光的频率相对于入射光的频率发生移动。非弹性散射又分为两类:拉曼散射与布里渊散射。拉曼散射与物质的分子结构有关,而布里渊散射实际上是由多普勒效应引起的,它和海水中的温度和盐度等密切相关。通过分析海洋悬浮粒子的布里渊散射特性,可以构建海洋悬浮粒子水体的温度和盐度检测模型。通常情况下,海水中水分子比光波波长小很多,可以用瑞利散射理论来描述其散射特性;而海洋悬浮粒子主要包括浮游植物和非色素悬浮粒子这两大类,其粒子的密度、大小、分布极其复杂,还没有严格的描述理论。目前,利用瑞利散射理论研究水分子的散射特性已经比较成熟,而针对海洋中浮游植物散射系数的研究,较多的采用基于叶绿素浓度的经验公式来计算其散射系数的大小,具有一定的不准确性,同时通过经验公式难于分析其散射系数特性;针对海洋中复杂的非色素悬浮粒子,也主要依靠经验公式来计算其散射系数,目前还有很多不成熟的地方。同时,描述海水中浮游植物和非色素悬浮粒子等海洋悬浮粒子后向散射率特性的严格理论还不存在,使得其后向散射率的具体数值一直难于计算。本文针对上述问题重点利用等效球的米氏散射理论分析研究了海洋悬浮粒子的散射特性,首先提出了利用散射效率因子来计算海洋悬浮粒子散射系数的公式,解决了浮游植物和非色素悬浮粒子等海洋悬浮粒子散射系数计算不准确的问题,同时还可以有效分析其散射系数特性。接着,提出了利用散射相函数来计算浮游植物和非色素悬浮粒子等海洋悬浮粒子后向散射率的公式,可以准确的计算出海洋悬浮粒子后向散射率的大小,而且还可以有效的分析其后向散射率特性。目前,利用布里渊散射技术检测海水温度是通过检测海水中布里渊散射信号的频移量来实现的,在这一过程中,通常是假定海水盐度为一定值,这样就存在较大的测量误差,同时还不能够测量海水的盐度信息。本文在分析海洋悬浮粒子布里渊散射特性的基础之上,引入了布里渊散射信号功率这一变量,利用布里渊散射信号的频移量和功率两个参量分别建立了海水温度和盐度检测的理论模型,能够实现对海水温度和盐度的检测。通过对布里渊散射激光雷达检测系统的研究,针对470nm到550nm光谱区域范围内的碘127分子吸收滤波器吸收谱线进行了仿真,并在此范围内寻找合适的吸收谱线,完成了整个探测系统鉴频器的设计,分析了满足探测需要的激光单稳频指标,在此基础之上,选择了合适的探测激光器。文章结合机载激光雷达技术,对该研究应用于海洋悬浮粒子的监测进行了仿真分析。针对海洋赤潮的监测应用,文章以探测海洋赤潮密度信息为基础,以检测海洋赤潮水体温度、盐度两个参量为辅助,不仅从本质上解决了悬浮泥沙和水分子对回波信号的影响,而且利用多个参数更加准确、直接的反映出赤潮消长的有关信息,比单参数预报方法有更高的预报精度,为实际海洋赤潮的监测和预报提供理论支持和技术指导。针对入海口悬浮泥沙颗粒的检测应用,文章利用蓝绿激光能够穿透浑浊的海水,有效的检测海洋悬浮泥沙颗粒的密度信息,为实际的入海口悬浮泥沙颗粒浓度检测提供了指导。通过对海洋悬浮粒子的米氏散射特性和布里渊散射特性研究,为实际海洋环境监测的实现提供了必要的理论支持,在海洋赤潮、入海口泥沙等海洋环境监测巡航、预报、应急与跟踪监视等方面具有广阔的环境、社会和经济效益前景。更多还原

【Abstract】 The optical scattering characteristics of oceanic suspended particles can directly affect the transmitting property of laser in seawater, and they are also significant theory basement of oceanic environmental optics detecting. When a beam of light is emitted into seawater, elastic scattering and non-elastic scattering will occur due to the combined action of light and water. The frequency of elastic scattering light has no shift. While the scattering characteristics are depended on incident wavelength, attribute of seawater, size and density of suspended particles and so on. The main scattering elements which provoke elastic scattering in seawater are water molecules and suspended particles. Elastic scattering usually contains Rayleigh scattering, Mie scattering and non-selective scattering. Water molecules mainly provoke Rayleigh scattering, while suspended particles mainly provoke Mie scattering. People can get information about the dimension and density of suspended particles by doing research on Mie scattering characteristics of suspended particles. Another scattering activated by light and water is non-elastic scattering. The frequency of such scattering light has a shift. Non-elastic scattering is divided into two kinds: Raman scattering and Brillouin scattering. Raman scattering is related to molecule structure of substance, while Brillouin scattering is introduced duo to Doppler Effect. And Brillouin scattering is closely related to the temperature and salinity of seawater. After analyzing the Brillouin scattering characteristics, the temperature and salinity detecting model of oceanic suspended particles can be established.In ordinary occasion, water molecule in seawater is smaller than wavelength of light, and its scattering characteristics can be described by Reyleigh scattering theory. Suspended particles mainly contain phytoplankton and non-algal particles. The density, dimension and distribution of these particles are quite complex, and there are no strict theory to describe them. Nowadays, the technology of studying scattering characteristics of water molecules with Rayleigh theory is more and more mature. About the research of scattering coefficient of marine phytoplankton, people usually use empirical equation of chlorophyll density to calculate it. This method has a rather large error. It is difficult to analyze the characteristics of scattering coefficient by empirical equation either. The scattering coefficient of complex non-algal particles is also depended on empirical equation. They all have immature aspects. Meanwhile, the strict theory to describe the characteristics of back scattering power is not existed yet. This leads to the difficulty to calculate the concrete value of scattering power.Focusing on the problems above, making use of equivalent sphere Mie scattering theory, this paper analyzes the scattering characteristics of oceanic suspended particles. At first, it promotes a formula to calculate scattering coefficient of suspended particles using scattering efficiency factor. This solves the inaccuracy problems to calculate the scattering efficiency of phytoplankton and non-algal particles, and it can analyze the characteristics of scattering coefficient effectively. Then, the formulas of back scattering efficiency of phytoplankton and non-algal particles are deduced using scattering phase function. These can accurately calculate the back scattering efficiency of suspended particles, and analyze the characteristics of back scattering coefficient effectively.At present, the realization of detecting temperature of seawater using Brillouin scattering theory relies on the detecting of frequency drift of Brillouin scattering signal. During the process, the salinity of seawater is usually considered as a constant. This leads to a large measurement error, and at the same time, the salinity of seawater can’t be detected. This paper bases on the research of Brillouin scattering characteristics of oceanic suspended particles, introduces a variable of Brillouin scattering energy, separately establishes detecting model of temperature and salinity of seawater using the frequency drift and energy parameters of Brillouin scattering signal, and finally realizes simultaneous measurement of temperature and salinity of seawater. The paper designs Brillouin scattering detecting system of lidar, simulates the absorption spectrum of I2127 in the range of wavelength between 470nm and 550nm, finds out appropriate absorption line, and completes the final design of frequency discriminator system. It analyses the proper monochromatic and stable frequency indexes that satisfy the detecting system’s demand, and makes a proper choice of detecting laser.Based on airborne lidar technology, this paper simulates the detecting of oceanic suspended particles. Targeting the application of marine red tide, taking the detecting of density of red tide as foundation, and the detecting of temperature and salinity as accessory, the paper not only essentially solves the effect of suspend sand and water molecule to echo signal, but also more accurately and directly reflects correlated information of red tide with multi-parameter, which has higher forecast precision than one-parameter forecast method. It supplies necessary theory foundation and technical support for real detecting and predicting of marine red tide. Targeting the detecting application of suspended particles in entrance of the ocean, making use of the information that blue-green laser can penetrate turbid seawater to detect density of suspended particles; the paper provides a foundation to real suspended particles density detecting. According to the detecting of Mie scattering and Brillouin scattering characteristics of oceanic suspended particles, this paper supplies necessary theory foundation for realization of practice system, and holds wide environment, society and economy benefit foreground in oceanic red tide detecting, suspended particles detecting, cruise, forecast, emergency and track.更多还原