合肥上空大气二氧化碳Raman激光雷达探测研究

Raman激光雷达是用于大气成分探测与特性研究的有效工具.介绍了中科院安徽光学精密机械研究所自行研制的一台用于测量低对流层大气CO₂时空分布的Raman激光雷达系统,并进行了一系列观测实验和对比分析.系统选用波长355 nm的紫外激光作为光源,利用光子计数卡双通道采集大气中N₂和CO₂的Raman后向散射信号与Li-7500型H₂O/CO₂分析仪进行对比标定,通过反演获得了大气CO₂水平与垂直方向时空分布廓线,并且获得了合肥地区大气边界层CO₂的夜变化趋势.结果表明,大气CO₂在空间的分布相对均匀,Raman激光雷达与CO₂分析仪变化趋势一致性较好,能够对大气CO₂时空分布进行有效、连续的观测.     

拉曼激光雷达探测低对流层大气二氧化碳分布

介绍了中国科学院安徽光学精密机械研究所研制成功的我国第一台测量低对流层大气CO2时空分布的拉曼激光雷达系统,选用波长355nm的紫外激光作为光源,利用光子计数卡双通道采集大气中N2和CO2的拉曼后向散射信号。详细分析了拉曼激光雷达系统的定标方法,提出采用Li7500型H2O/CO2分析仪与拉曼激光雷达系统进行对比与标定,结果显示激光雷达与CO2分析仪数据变化趋势一致性较好,激光雷达具有很高的探测灵敏度与准确性,通过线性拟合水平方向标定误差小于0.2%,垂直方向小于1.4%。由标定关系反演出大气中CO2的时空分布,给出了合肥西郊低对流层大气CO2水平方向0～2.0km与垂直方向0～2.5km分布的典型测量结果。     

银川上空大气气溶胶光学特性激光雷达探测研究

小型米散射激光雷达是广泛使用的探测大气气溶胶光学特性的有效工具。作者研制了一台小型米散射激光雷达,并利用该激光雷达于2009年4月1日至4月10日期间对宁夏银川地区(北纬38°29′, 东经106°06′)上空的大气气溶胶光学特性以及时空分布进行了观测。系统选用532 nm波长激光作为光源,采用Fernald法对接收到的大气回波信号进行反演,得到了气溶胶消光系数的高度分布廓线及24 h内气溶胶消光系数相对浓度的时空变化特性;并对期间一次明显的沙尘天气进行了观测和分析。观测结果表明,该小型米散射激光雷达能够对大气气溶胶及其时空分布情况进行有效、连续的观测,其观测结果有利于分析该地区气溶胶及沙尘天气的变化趋势。     

小型米散射激光雷达的研制及其探测

介绍了一台自行研制的用于大气气溶胶光学特性和水平能见度测量的小型米散射激光雷达系统,并进行了一系列观测实验和分析.系统选用532nm波长激光作为光源,采用Fernald反演算法对接收到的大气回波信号进行反演得到气溶胶消光系数.通过对西安城区上空的气溶胶光学特性进行连续观测,测得了西安城区不同时刻消光系数的高度分布廓线、以及24小时内大气边界层高度的时空变化特性,并对大气水平能见度进行了连续观测,其结果与当地气象部门提供的水平能见度数据的变化趋势基本一致.观测结果表明,利用该米散射激光雷达可以对大气气溶胶光学特性和水平能见度进行有效测量.     

用于大气温度廓线测量的瑞利-拉曼激光雷达

大气温度廓线及其时间演变特征资料在地球科学领域具有重要的应用,为获取高时空分辨的大气温度的垂直分布,建立了瑞利-拉曼温度测量激光雷达。介绍了瑞利-拉曼激光雷达进行温度测量的主要原理和研制的瑞利-拉曼激光雷达的主要参数;数据处理方面,通过背景噪声剔除和小波算法降噪提高系统的信噪比;使用研制的激光雷达对大气温度廓线进行观测,将观测结果与大气模式数据和卫星观测结果进行对比,均显示较好的一致性,证明了激光雷达温度测量结果的准确性,其温度测量数据可以用于气象学研究。     

探测大气中CO2的Raman激光雷达

基于大气激光后向散射光谱,研究和设计了探测大气CO2浓度的Raman激光雷达,其发射机采用Nd:YAG激光的三倍频354.7nm作为工作波长,发射的单脉冲能量350mJ,重复频率20Hz;接收机采用了光电倍增管(量子效率25%)和光子计数器(计数速率200MHz),探测CO2的Raman散射371.66nm(频移1285cm-1信号,(1小时累加)近地面2.5km以内信噪比不小于8.采用组合滤光片来抑制强的354.7nm Mie-Rayleigh后向散射和氧气375.4nm Raman后向散射对信号的严重干扰.比较分别来自大气CO2和参考气体N2的Raman后向散射回波,可反演出大气中CO2的相对浓度.     

大气信道对红外激光通信系统性能影响的实验研究

针对近地面、准水平红外激光大气通信系统的应用,利用微脉冲激光雷达、大口径激光闪烁仪在济南市区进行了为期一周的昼夜连续观测,获得了影响红外激光通信系统性能的关键大气参量的信息.着重分析了大气衰减信道、大气湍流信道对一公里通信链路系统性能的影响,考查了通信设备在复杂大气条件下应用的可行性及可靠性.最后就减弱大气信道对通信性能影响的方法进行了总结和探讨.     

利用激光雷达测量都市上空气溶胶的浓度分布

测量都市上空气溶胶浓度分布的最方便方法是水平米散射激光雷达。因激光雷达是主动遥感监测系统,其测量距离可达到几公里,而且具有高时空分辨率的特点。同时,其设计也可以达到激光安全标准。本研究所用的激光雷达系统是安装在海拔118米高的山上。在观测时可以测量稠密市区上空的气溶胶分布与及监察从发电厂排放出的微粒。本文介绍这激光雷达系统的设计及激光雷达反演的方法。会对激光雷达量度的消光系数与大气监测的可悬浮粒子浓度之间的相关性进行考证。     

大气信道对红外激光通信系统性能影响的实验研究

针对近地面、准水平红外激光大气通信系统的应用,利用微脉冲激光雷达、大口径激光闪烁仪在济南市区进行了为期一周的昼夜连续观测,获得了影响红外激光通信系统性能的关键大气参量的信息.着重分析了大气衰减信道、大气湍流信道对一公里通信链路系统性能的影响,考查了通信设备在复杂大气条件下应用的可行性及可靠性.最后就减弱大气信道对通信性能影响的方法进行了总结和探讨.     

PM2.5质量浓度廓线的激光雷达反演研究

针对PM2.5质量浓度在空间不同高度上的分布测量较难这一问题,采用激光雷达和大气透射仪以及粒径谱仪进行联合探测,反演PM2.5质量浓度廓线.考虑相对湿度等因素的影响,通过大气透射仪和粒径谱仪建立地面PM2.5质量浓度与大气透过率之间的函数关系.以大气透射仪所测地面大气透过率值为基准,修正激光雷达大气透过率在高空的边界值,结合Fernald后向积分法反演出大气透过率的垂直分布.依据建立的函数关系和大气透过率垂直分布,得到PM2.5质量浓度廓线,并采用HYSPLIT后向轨迹分析不同高度层气溶胶的输送和动态变化.通过激光雷达、大气透射仪和粒径谱仪的联合探测实验,结果表明:经大气透射仪修正后,大气透过率垂直分布精度得到了提高,PM2.5质量浓度廓线很好的反映了气溶胶垂直分布的微物理变化特征.     

Capability of Raman lidar for monitoring the variation of atmospheric CO2 profile

Lidar （Light detection and ranging） has special capabilities for remote sensing of many different behaviours of the atmosphere. One of the techniques which show a great deal of promise for several applications is Raman scattering. The detecting capability, including maximum operation range and minimum detectable gas concentration is one of the most significant parameters for lidar remote sensing of pollutants. In this paper, based on the new method for evaluating the capabilities of a Raman lidar system, we present an evaluation of detecting capability of Raman lidar for monitoring atmospheric CO2 in Hefei. Numerical simulations about the influence of atmospheric conditions on lidar detecting capability were carried out, and a conclusion can be drawn that the maximum difference of the operation ranges caused by the weather conditions alone can reach about 0.4 to 0.5km with a measuring precision within 30ppmv. The range of minimum detectable concentration caused by the weather conditions alone can reach about 20 to 35 ppmv in vertical direction for 20000 shots at a distance of 1 km on the assumption that other parameters are kept constant. The other corresponding parameters under different conditions are also given. The capability of Raman lidar operated in vertical direction was found to be superior to that operated in horizontal direction. During practical measurement with the Raman lidar whose hardware components were fixed, aerosol scattering extinction effect would be a significant factor that influenced the capability of Raman lidar. This work may be a valuable reference for lidar system designing, measurement accuracy improving and data processing.     

基于Fizeau干涉仪的激光雷达测温方法研究

气温是描述大气状态的基本参数之一,温度的准确测量对天气预报、气候预测及其他气象参数的反演都至关重要。激光雷达作为一种遥感仪器,已经用于气象要素的探测中（风、温度、气溶胶的光学厚度等）。目前,测温激光雷达主要有拉曼激光雷达（振动和转动）、共振荧光激光雷达和Rayleigh散射激光雷达等,拉曼激光雷达需要大功率的激光器和复杂的背景滤波器;共振荧光激光雷达无法探测平流层内的温度;基于Rayleigh散射的测温激光雷达多应用于温度的相对测量,反演温度时需要建立响应函数和校准程序;基于固体腔扫描F-P干涉仪测量大气Rayleigh散射光谱来反演温度的方法,时间分辨率较低,并且该方法在测量过程中需要运动部件,所以不利于星载。在大气低层,分子的Rayleigh散射光谱会受到Brillouin散射的影响,两种散射信号叠加形成的Rayleigh-Brillouin散射光谱不再服从Gaussian分布,直接通过测量散射光谱的半高全宽来反演温度,会产生误差。基于回波能量的方法会受到气溶胶Mie散射信号的影响,所以在对流层中该方法并不适用。为了实现对流层内温度的高精度和高时间分辨率的测量,提出利用Fizeau干涉仪和PMT阵列对对流层内分子的Rayleigh-Brillouin散射光谱进行测量,并通过插值的方法来对回波信号中气溶胶Mie散射信号进行抑制,从而使Mie散射信号对温度反演的影响较小,最后将测量光谱和理论光谱进行全光谱匹配来实现温度的反演。除此之外,还对Fizeau干涉仪的自由光谱区、固体腔几何长度、腔体反射率、扫描间隔等参数进行了优化设计。为了验证本文提出方法的可行性,利用Matlab软件建立了一套仿真模型,通过模拟表明,在不考虑云、风和水汽含量的影响时,利用该方法测量对流层内的大气温度时,测量误差小于1 K。该测温方法可以对对流层内的大气温度廓线实现高精度、高时间分辨率的测量, 在测量过程中不需要使用运动部件,有较高的使用价值,并对同类高光谱激光雷达分光系统的研究具有借鉴意义, 为我国高光谱激光雷达陆基及星载应用提供了一套可行的技术方案和温度反演方法。     

Capability of Raman lidar for monitoring the variation of atmospheric CO2 profile

Lidar (Light detection and ranging) has special capabilities for remote sensing of many different behaviours of the atmosphere. One of the techniques which show a great deal of promise for several applications is Raman scattering. The detecting capability, including maximum operation range and minimum detectable gas concentration is one of the most significant parameters for lidar remote sensing of pollutants. In this paper, based on the new method for evaluating the capabilities of a Raman lidar system, we present an evaluation of detecting capability of Raman lidar for monitoring atmospheric CO$_{2}$ in Hefei. Numerical simulations about the influence of atmospheric conditions on lidar detecting capability were carried out, and a conclusion can be drawn that the maximum difference of the operation ranges caused by the weather conditions alone can reach about 0.4 to 0.5km with a measuring precision within 30ppmv. The range of minimum detectable concentration caused by the weather conditions alone can reach about 20 to 35 ppmv in vertical direction for 20000 shots at a distance of 1 km on the assumption that other parameters are kept constant. The other corresponding parameters under different conditions are also given. The capability of Raman lidar operated in vertical direction was found to be superior to that operated in horizontal direction. During practical measurement with the Raman lidar whose hardware components were fixed, aerosol scattering extinction effect would be a significant factor that influenced the capability of Raman lidar. This work may be a valuable reference for lidar system designing, measurement accuracy improving and data processing.     

Analysis of influence of atmosphere extinction to Raman lidar monitoring CO2 concentration profile

Lidar （Light detection and ranging） system monitoring of the atmosphere is a novel and powerful technique tool. The Raman lidar is well established today as a leading research tool in the study of numerous important areas in the atmospheric sciences. In this paper, the principle of Raman lidar technique measurement CO2 concentration profile is presented and the errors caused by molecular and aerosol extinction for CO2 concentration profile measurement with Raman lidar are also presented. The standard atmosphere extinction profile and ＇real-time＇ Hefei area extinction profile are used to conduct correction and the corresponding results are yielded. Simulation results with standard atmosphere mode correction indicate that the errors caused by molecule and aerosol extinction should be counted for the reason that they could reach about 8 ppm and 5 ppm respectively. The relative error caused by Hefei area extinction correction could reach about 6%. The errors caused by the two components extinction influence could produce significant changes for CO2 concentration profile and need to be counted in data processing which could improve the measurement accuracies.     

Raman激光雷达探测气溶胶光学特性

介绍了武汉大学自行研制的Raman多通道激光雷达系统,给出了整个系统的设计原理及主要技术参量.详细描述了利用Raman激光雷达原理反演大气气溶胶消光系数、后向散射系数和激光雷达比等光学特性的方法,并对求解消光系数过程中的关键部分做了讨论分析.同时对武汉上空对流层低空大气气溶胶、云以及边界层等光学特性进行了实时探测反演.实验结果表明:该Raman多通道激光雷达系统在夜晚对低空气溶胶的垂直分布特性具有较好的探测能力,工作性能可靠.     

Measurement of tropospheric CO2 and aerosol extinction profiles with Raman lidar

A prototype Raman lidar was designed for monitoring tropospheric CO2 profile and other scientific investigatious.The third harmonic of Nd:YAG laser (354.7-nm wavelength) was used as stimulated light source to provide nighttime measurements.Filter with high rejection ratio performance was used to extract CO2 Raman signals from Rayleigh-Mie scattering signals effectively.To improve the real time monitoring function,a two-channel signal collection system was designed to collect CO2 and N2 Raman scattering signals simultaneously. The N2 Raman scattering signals were used to retrieve aerosol extinction coefficient.Typical features of CO2 concentration profile and aerosol extinction coefficient in Herei were presented.The mixing ratio of atmospheric CO2 in Hefei can reach about 360-400 ppmv.     

Mie scattering techniques for air pollution measurement with lasers

Lidar (laser radar) techniques of remotely observing atmospheric particulates have obvious relevance to air pollution. After briefly noting the capability of lidar in a semiquantitative role for monitoring spatial and temporal variations of particulate concentration attention is directed to the problems of evaluating lidar observations quantitatively in terms of such physically meaningful parameters as the turbidity, opacity or particulate mass concentration of smoke plumes or the ambient atmosphere. Solutions based on Mie scattering theory are illustrated with examples from (1) hazy atmospheres (2) smoke plumes and (3) controlled aerosols in a test chamber. While noting that the role of lidar in research applications in air pollution is well established, its routine operational use is seen to be dependent upon further experimental and technological development. Its potential for monitoring ambient air quality and emission sources is stressed.     

Differential optical absorption spectroscopy measurement of CO2 using a nanosecond white light continuum

We built a differential optical absorption spectroscopy system to measure near-surface CO2 absorption in the atmosphere using a nanosecond white light continuum. The white light laser can cover wavelengths ranging from 420 to 2400 nm, where the CO2 and H2O absorption lines are located. At an optical path length of 568 m, it was possible to evaluate atmospheric CO2 concentration from absorption bands of CO2 and H2O in the vicinity of 2000 nm detected by broadband white light simultaneously.