Remote sensing of air pollution incorporating integrated-path differential-absorption and coherent-Doppler lidar

An innovative complex lidar system deployed on an airborne rotorcraft platform for remote sensing of atmospheric pollution is proposed and demonstrated.The system incorporates integrated-path differential absorption lidar(DIAL) and coherent-doppler lidar(CDL) techniques using a dual tunable TEA CO_(2)laser in the 9—11 μm band and a 1.55 μm fiber laser.By combining the principles of differential absorption detection and pulsed coherent detection,the system enables agile and remote sensing of atmospheric pollution.Extensive static tests validate the system’s real-time detection capabilities,including the measurement of concentration-path-length product(CL),front distance,and path wind speed of air pollution plumes over long distances exceeding 4 km.Flight experiments is conducted with the helicopter.Scanning of the pollutant concentration and the wind field is carried out in an approximately 1 km slant range over scanning angle ranges from 45°to 65°,with a radial resolution of 30 m and10 s.The test results demonstrate the system’s ability to spatially map atmospheric pollution plumes and predict their motion and dispersion patterns,thereby ensuring the protection of public safety.

Atmospheric NO_2 Concentration Measurements Using Differential Absorption Lidar Technique

Using the Differential Absorption Lidar (DIAL) technique, two types of approaches, namely, reflection from retroreflector / topographic target and backscatter from atmosphere, are available for studying remotely the atmospheric NO, concentration. The Argon ion lidar system at the Indian Institute of Tropical Meteorology (IITM), Pune, India has been used for the measurements by following both the path-averaged and range-resolved approaches. For the former, a topographic target (hill) is used for determining path-averaged surface concentration. In the latter, spectral properties of atmospheric attenuation is used for making range-resolved measurements in the surface layer. The results of the observations collected by following both approaches are presented. The average surface NO2 concentration was found to vary between 0.01 and 0.105 ppm and the range-resolved measurements exhibited higher values suggesting treatment of the lidar data for scattering and extinction effects due to atmospheric aerosols and air molecules, and atmospheric turbulence. Certain modifications that are suggested to the experimental set-up, data acquisition and analysis to improve the measurements are briefly described.

Effect of Atmospheric Scintillation on SNR of Differential Absorption Lidar System

In this paper, the effect of scintillation on system SNR is discussed. Atmospheric scintillation is described and log amplitude variance in slant path is given. In addition, the simulations of system SNR at different propagation path and different height are obtained. The results from simulation show that atmospheric scintillation has an important effect on SNR of DIAL system, especially near the ground.

Simultaneous Monitoring of Nitrogen Dioxide and Aerosol Concentrations with Dual Path Differential Optical Absorption Spectroscopy

Differential optical absorption spectroscopy (DOAS) is a useful technique for measuring nitrogen dioxide (NO2) and aerosol, the most important species in urban environmental pollution. This paper reports on the results of our dual path DOAS measurements recently conducted in Chiba City, Japan, using xenon flashlights equipped on tall constructions as aviation obstruction lights. Because of the proximity of the southern DOAS path to an industrial area, it is found that the level of air pollution generally increases with the dominance of westerly winds, from the plausible source area to the observation light path. This situation is consistent with the result of wind lidar measurement covering a sector of ±28? with the observation range of approximately 2.8 km. In spite of the fact that the two DOAS paths, having path lengths of 5.5 and 3.5 km each, are located in separated regions of Chiba City, the observed temporal behavior was similar for both nitrogen dioxide and aerosol, though the southern path tends to exhibit slightly higher pollution levels than the northern counterpart. Additionally it is confirmed that size information of aerosol particles can be derived from the DOAS data through the analysis of the wavelength dependence of the aerosol optical thickness, which shows fairly good correlation with the mass ratio between PM2.5 and suspended particulate matter (SPM) obtained from the in-situ sampling station measurement. Thus, the DOAS approach can also be utilized for obtaining information on PM2.5 that is considered to be more harmful to human health than SPM.

Return Signal Intensity Ratio Modulates the Impact of Background Signal on Ozone DIAL Night Time Measurement in the Troposphere

This paper discusses the uncertainty of ozone differential absorption lidar (DIAL) measurements due to the impact of background signal. The impact of background signal on ozone concentration profiles is proportional to the background intensity and the ratio of return signal intensities at “on” and “off” wavelength ( ) (hereinafter we call it the return signal intensity ratio). Analysis suggests that an appropriate return signal intensity ratio can make the impact of background signal very small, negligible. The simulations based on the analysis coincide with the experimental results. The experimental results show that the impact of background signal is negligible at an appropriate return signal intensity ratio of 0.96 at wavelength pair (280,285 nm). In case of unknown background intensity, we can adjust the laser pulse energy levels at the two wavelengths to obtain an appropriate return signal intensity ratio on the oscilloscope to suppress the impact of background signal and ensure the accuracy of night time ozone measurements.

大气环境监测卫星激光雷达技术

星载激光雷达是高精度测量全球大气CO_(2)柱浓度和气溶胶垂直廓线的重要手段,大气环境监测卫星大气探测激光雷达(ACDL)在一套激光雷达中集成了2种探测体制,采用1572 nm积分路径激光差分吸收方法测量全球CO_(2)柱浓度,采用532 nm高光谱探测(HSRL)方法测量气溶胶和云的垂直廓线,均为国际首次在星载平台成功验证,是国际首个星载CO_(2)探测激光雷达和国际首个高光谱气溶胶探测激光雷达。在国际已发射的星载激光雷达中,ACDL激光雷达是探测体制最全、波长最多、能量最高、频率最稳和精度最准的激光雷达,实现了创新跨越。大气探测激光雷达在轨连续工作,首次获得了全天时精度优于1×10-6的全球CO_(2)柱浓度、精度优于20%的气溶胶廓线等遥感数据。本文介绍了ACDL激光雷达的工作原理、系统参数以及相关的定标测试结果。

星载二氧化碳探测研究进展

二氧化碳(CO_(2))是大气中最典型的温室气体,大气中CO_(2)浓度持续增加是全球气温升高的主要原因。温度升高导致自然环境恶劣,各类自然灾害频发,极端天气数量增加,对人类生活环境造成巨大的影响,因此推动绿色低碳发展势在必行。准确监测CO_(2)的排放,了解CO_(2)源和汇的分布,是遏制大气CO_(2)浓度升高、减缓全球变暖的前提条件。因此,准确获取全球范围内高精度时空分辨率的CO_(2)观测数据十分必要。卫星遥感可以有效观测CO_(2)的全球分布,获取大范围高精度数据。本文旨在对目前用于大气CO_(2)探测的卫星载荷发展状况进行综述,包括基于被动遥感CO_(2)的卫星现状和数据产品、基于主动遥感CO_(2)的卫星的研制情况和目前的主要工作进展。

臭氧激光雷达技术及应用研究进展

差分吸收臭氧激光雷达是完善光化学立体监测体系的重要技术,因其高时空分辨率的廓线探测优势而得以迅速发展,目前已被广泛应用于对流层臭氧浓度的遥感探测。阐述了臭氧激光雷达的原理,归纳总结了雷达系统及关键技术的国内外最新研究进展,梳理了臭氧激光雷达在环境领域的应用现状,并基于我国城市臭氧污染问题现状和管理需求,初步探索设计了臭氧激光雷达监测网络业务应用的整体框架。指出了臭氧激光雷达技术及应用中存在厂家众多但缺乏统一的技术规范和行业标准,数据质量及准确性有待提高,与标准分析方法产生数据的可比性较差等不足之处;提出了核心部件国产化,系统小型化、自动化及商用化,多平台以及与其他监测方式联用等发展趋势。

利用激光雷达探测潍坊市夏季臭氧分布特征

为了研究潍坊市夏季臭氧的分布特征,使用差分吸收激光雷达在潍坊市进行观测,分析了晴天和雨天臭氧分布的差别,并统计了无降水日臭氧的垂直分布和日变化特征。结果表明:降水发生前强烈的对流运动和大风会使对流臭氧层变厚,臭氧浓度变低;降水发生在一天中的不同时段,对臭氧污染的影响差异很大;无降水日对流臭氧层主要分布在1500 m以下,呈现白天高、夜晚低的日变化特征,高浓度值常出现在12~18时;在垂直结构上呈现分层的特征,其中,300~500 m高度的臭氧浓度随着高度的增加而增大,且在500 m附近达到极大值,该高度和米散射激光雷达探测的边界层高度基本一致;1500 m高度各个时段的臭氧浓度趋于一致,且自该高度往上臭氧无明显日变化特征,可将该层臭氧浓度作为臭氧预报的大气背景值。

中红外差分吸收激光雷达探测苯气体浓度

苯作为挥发性有机化合物(VOCs)的重要组成部分,其大气污染状况日益引起人们的关注,中红外波段通常是分子的基频指纹吸收区,已成为痕量气体检测的重要波段,而差分吸收激光雷达是探测大气痕量气体的重要手段,故针对区域性苯浓度实时遥感问题,提出基于中红外带间级联激光器(ICL)的探测大气苯浓度路径积分型差分吸收(IPDA)激光雷达系统。首先,在分析IPDA激光雷达的探测原理的基础上,构建了IPDA激光雷达的反演算法及其误差分析模型。其次,详细分析来自HITRAN数据库的中红外3100 cm^(-1)附近苯以及主要干扰气体(如HCl,CH_(4)和H_(2)O)的吸收光谱,结合HCl和CH_(4)着重考虑了H_(2)O对探测结果的影响,选择IPDA激光雷达的测量波长和参考波长分别为3090.89和3137.74 cm^(-1)。再次,基于两个连续波ICL,设计了探测大气苯浓度IPDA激光雷达系统,并可通过控制温度和驱动电流调谐激光器的输出波长,使其波长分别稳定在强吸收谱区和弱吸收谱区,并设计了基于中红外衍射光栅的光谱分光子系统,以实现双波长接收信号的同步探测。最后,基于标准大气模型,仿真分析了不同路径长度、能见度和水汽浓度情况下激光雷达的探测性能,并搭建中红外波段检测气体池开展了测试实验,以验证该IPDA激光雷达系统的可行性。仿真及实验结果分析表明,当大气能见度为5 km,水汽浓度低于0.4%时,苯的浓度路径积(CL)在0.1~24 mg·m^(-3)·km范围内探测的相对误差优于10%,而苯的CL为5 mg·m^(-3)·km时探测相对误差优于1%;初步实验测试了中外红波段差分吸收激光雷达探测的线性相关系数R^(2)约为98.7%。

大气探测激光雷达校飞样机研制与飞行验证

星载激光雷达是高精度测量全球温室气体和气溶胶垂直廓线的重要手段,大气环境监测卫星大气探测激光雷达(ACDL)在国际首次采用激光积分路径差分吸收技术测量全球CO_(2)柱浓度,采用532 nm高光谱探测技术测量气溶胶和云的廓线。星载激光雷达载荷研制期间,同步研制一套主要功能一致的机载大气探测激光雷达校飞样机,并开展机载飞行试验,获取了大量飞行试验及其对比数据,提供了机载平台真实的数据源,对于优化ACDL激光雷达系统参数和研究星载数据反演算法至关重要。最后在机载飞行平台下,验证了优于1×10^(-6)的CO_(2)柱浓度测量精度和优于15%的气溶胶测量精度。未来利用该机载样机可以进一步开展星地对比验证。

A new differential absorption lidar for NO_2 measurements using Raman-shifted technique

Based on Raman-shifted wavelengths of D2 and CHr pumped by third harmonic of Nd:YAG laser, a differential absorption lidar was presented in this paper and had been constructed for probing environmental NO2 concentration. NO2 experimental measurements were carried out at Anhui Institute of Optics and Fine Mechanics in Hefei. Some NO2 measurement results were given and discussed.

差分吸收激光雷达测量对流层臭氧

利用激光雷达对对流层 2～ 4km高度范围的臭氧分布进行了测量。测量结果表明 ,利用YAG激光器产生的两个波长 (2 6 6nm和 2 89nm) ,可以得到比较精确的臭氧分布。

差分吸收激光雷达测量NO_2浓度的实验研究

介绍了差分吸收激光雷达测量大气中物质成份及浓度的测量原理,并利用差分吸收激光雷达测量了3.5 km内NO2的浓度分布,测量结果表明,使用双通道可调谐的Ti:Sapphire激光器的一组波长(448.2nm和446.8 nm)可以获得比较精确的NO2的浓度随距离的分布。

国外差分吸收激光雷达探测大气CO2研究综述

差分吸收激光雷达是探测大气CO_2时间和空间分布不可或缺的工具。2.0μm波段Ho:Tm:YLF或Ho:Tm:LuLiF激光器复合外差接收机,1.6μm种子注入的KTP光参量振荡器或参量发生器复合光电倍增管的光子计数技术,可以探测7 km以下对流层大气CO_2混合比的分布。调制连续波种子激光强度、共用1.6μm光纤放大器,以及相关检测技术的使用,积分路径差分吸收激光雷达在大气CO_2柱浓度探测方面具有独特的优点和特色。探测大气二氧化碳柱浓度的空间计划有美国NASA的ASENDS计划,采用脉冲式、积分路径差分吸收工作方式。用CO_2气体吸收池作为参照物,稳定种子光频率和精确控制谐振腔长,锁定发射机的on光源波长,是差分吸收激光雷达探测大气二氧化碳的关键技术。

探测低空大气CO_2浓度分布的近红外微脉冲激光雷达

提出了用来探测大气CO2 分布、基于光纤 1.6um波长的微脉冲激光雷达 ,对其性能进行了数值模拟 .微脉冲激光雷达的发射机以半导体激光器加光纤放大器为核心 ,饱和输出功率 37dBm ;接收机采用了近红外光电倍增管和光子计数器 ,量子效率 1% ;一种偏正无关性纤维光学环形器作为发射 /接收转换器 ,分波 /合波器、隔离器、滤波器、耦合器都采用光纤器件 ,使系统更牢固 .该系统的特点是发射脉冲能量低 2 0uJ、重复频率高 2 0KHz、小型化 .(18× 10 6个脉冲累加 )它对近地面 4 .7Km高度内的探测信噪比在 10∶1以上 .光电倍增管的暗计数 2× 10 5/s限制了系统探测距离的增加 .吸收倍增分离的InGaAs/Si雪崩光电二极管将会改善雷达的性能 .

快速调谐小型TEA CO_2激光器的实验研究

报道了可用于 CO2 激光差分吸收雷达光源的一小型快调谐 TEA CO2 激光器。调谐机构由单片机控制的高频步进电机、衍射光栅、触发控制器组成。在谐振腔长 50 0 mm、脉冲重复率 2 0 Hz的 TEA CO2 激光器中 ,实验得到零级输出谱线四十一条 ,一级输出谱线二十条 ,每脉冲输出能量～ 2 0 m

基于差分吸收激光雷达的云消除算法研究

差分吸收激光雷达测量臭氧浓度过程中,云层信号会造成对流层臭氧浓度剧烈的抖动,带来了很大的测量误差.本文提出了一种云消除算法,该算法通过插值云层高度区域内的臭氧浓度,有效消除了对流层臭氧浓度的剧烈抖动.通过阐述其理论基础,给出了其算法关键点,即云信号的识别和云高度的精确定位.根据云层消光系数的特点,通过设定气溶胶消光系数阈值获取云层高度信息,利用累加平均有效减少噪音造成的测量误差.结果表明,在精确确定云高、云底的基础上,运用线性插值算法对臭氧测量结果进行修正,可以有效克服云层对测量结果造成的急剧起伏.

基于差分吸收激光雷达的一种新的对流层臭氧浓度反演算法

差分吸收激光雷达探测对流层臭氧浓度时,气溶胶的干扰会造成较大的误差。提出了一种算法,该算法能够同时反演得到对流层臭氧浓度和气溶胶消光系数,减少气溶胶对反演结果的影响。使用实验数据,分析计算了气溶胶雷达比,气溶胶波长指数、标定点气溶胶后向散射比各种变化参数对反演结果的误差。结果表明,1km以下,各种变化参数造成的反演误差小于8%,1km以上臭氧浓度误差主要来源于信号和背景噪声,各种参数反演误差小于3%。最后给出了利用该算法得到对流层臭氧浓度和气溶胶的消光系数垂直廓线,并和传统的双波长差分算法反演结果作了比较分析。实验结果表明该算法是可行的,该算法可以减少气溶胶对差分吸收激光雷达测量结果引起的误差。

0.94μm差分吸收激光雷达地基工作的进展

为了更好地探测对流层大气水汽的垂直廓线,对已经建立的935 nm差分吸收激光雷达进行了部分改进。采取双通道接收的措施,近场通道望远镜同时也是发射激光的扩束器,近场通道采用偏振分束器加四分之一波片的方式隔离发射光和回波光,远场通道(主通道)采用平行旁轴的卡塞格林望远镜,从而减小激光雷达近地面盲区;发射机的双波长挪到936.0~936.5 nm之间,增加了注入种子激光的功率,提高发射光谱纯度,从而提高探测精度。探测范围从600~2000 m,延展到250~3000 m,随机误差5%。