【作者】 高飞；

【导师】 华灯鑫；

【作者基本信息】 西安理工大学 ， 测试计量技术及仪器， 2008， 硕士

【摘要】 大气气溶胶是研究大气物理及气候变化的一个非常重要的参数,其吸收、散射以及密度分布直接影响地球辐射平衡,大气气候环境变化以及空气质量污染指数。精细探测及研究气溶胶的产生,输送及其光学和物理特性的时空变化规律,对研究大气环境变化及提高自然灾害的预警预报能力,特别是研究全球气候变暖问题,沙尘暴的预警预报及城市气溶胶的物理光学特性具有重要的研究意义和社会效益。米散射激光雷达具有较高的时空探测分辨率,以及结构简单、易于操作等优点,已经成为实时探测气溶胶光学特性的强力工具之一。然而,由于一般的米散射激光雷达反演大气气溶胶光学特性时,需要对大气状态进行假设,从而限制了其测量精度。本论文主要针对现有米散射激光雷达存在的问题,提出并设计了利用拉曼散射及瑞利散射精细探测气溶胶光学特性的激光雷达技术,并通过实验及数值仿真对系统设计进行验证。拉曼散射激光雷达技术主要是利用大气分子的拉曼散射信号与气溶胶消光系数的依存关系,实现气溶胶消光系数的精确探测。系统分别选用Nd:YAG脉冲激光器的三倍频输出355nm和口径250mm的卡塞格林式望远镜作为发射和接收系统,高光谱分辨率的平面反射光栅结合由窄带反射镜组组建的滤波器,分离中心波长为387nm的大气氮气的振动拉曼散射回波信号。同时利用激励波长355nm的光栅一级衍射光作为米散射探测通道,用来验证拉曼激光雷达系统的可行性。两路探测通道都是由模拟探测方式下带有前置运放的光电倍增管进行光电探测。初步实验表明,在脉冲激光能量250mJ,探测时间为8分钟（约10000次脉冲累积平均）的情况下,设计的拉曼激光雷达系统具有对3km以下气溶胶光学特性精细探测的能力。高光谱分辨率激光雷达技术主要是通过设计高光谱分辨率分光器,分离大气气溶胶引起的米散射及大气分子引起的瑞利散射,从而实现气溶胶的精细探测。本系统选择具有种子注入技术的单频脉冲激光器的紫外输出355nm作为光源,高光谱分辨率闪耀光栅在空间上分离太阳背景光及激光大气回波信号,保证白天测量的需要,高光谱分辨率的Fabry-Perot标准具分离气溶胶米散射及大气分子瑞利散射信号,从而实现气溶胶及云光学特性的精细探测。系统利用标准大气模型对系统进行数值仿真结果表明,在太阳背景光能量密度0.3×10⁹Wm^-2sr^-1nm^-1的白天情况下,激光能量150mJ,探测时间1分钟的条件下,对气溶胶光学特性的有效探测高度可以达到10km以上。更多还原

【Abstract】 Atmospheric aerosol is one of the important parameters for investigating the atmospheric physics and climate change,because its absorption,scattering and distribution of density influence the balance of Earth’s radiation,atmospheric climate conditions and air pollution index directly.Fine-detection of the production,the transportation,optics and the physical property of aerosols as well as investigation of its space-time change rule have the significant research meaning and the social benefit to study the atmospheric environment,enhance early warning forecast ability of the natural disaster,especially to investigate the problem of global climate warming and the sand storm early warning forecast and the urban aerosol physical optics properties.Mie scattering lidar is one of the powerful tools for detection of the optical characteristics of aerosol with real-time because of its compactness,relatively low cost and easy of operation. However,because the retrieval of the optical properties of aerosol from the Mie lidar retum signal needs some assumption of weather conditions,which limits its measurement accuracy, therefore,the measurement uncertainty is still an intrinsic problem of the Mie lidar.In order to overcome the shortage of the Mie scattering lidar,in this paper,two kinds of lidar techniques which are based on Raman scattering and Rayleigh scattering,respectively,are proposed for fine-detection of aerosol profiles,and the feasibility of those lidar systems are confirmed by use of the experimental observation and the numerical simulation.Raman scattering lidar technique utilizes the dependence relationship between Raman scattering signal of atmospheric molecular and extinction coefficient of aerosol for fine detection of aerosol extinction profiles:A tripled Nd:YAG pulsed laser and a 250-mm-diameter Cassegrainian telescope are employed as transmitter and receiver respectively,a high-resolution plane reflection grating separates the vibrational Raman signal of N₂ at a central wavelength of 387nm.The first order of the grating（355nm）is used as Mie lidar to verify the feasibility of Raman method and to retrieve the aerosol extinction coefficient.The two scattering signals are detected by two photomultiplier tubes with a pre-amplifier in analog detection mode and recorded by analog-digital conversion.Preliminary experiments show that the Raman lidar system has the capability of fine-detection of aerosol profiles up to a height of 3km with 250mJ of laser energy and 8 minute integration time.High-spectral-resolution lidar（HSRL）technique separates the Mie-scattering signal caused by aerosol and Rayleigh-scattering signal caused by molecular by using the high-spectral-resolution spectroscopic filter,and then achieves accurate measurement of aerosol optical properties.An injection seeded single frequency pulsed Nd:YAG laser at 355nm is employed as the transmitter,a high-resolution blazed grating and a Fabry-Perot etalon filter are used to block the solar background and to separate the Rayleigh- and Mie-scattering components respectively.As a result,the aerosol extinction and lidar ratio can be obtained accurately without needs of assumption condition.The numerical simulation based on a standard atmospheric model shows that the lidar system has the capability of measuring the aerosols with a signal to noise ratio of more than 10 up to a height of 10km at daytime with 0.3×10⁹Wm^-2sr^-1nm^-1solar irradiance.更多还原