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.

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.

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.

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 .

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.

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。

基于差分吸收激光雷达有毒有害气体遥测进展

差分吸收激光雷达具有探测距离远、灵敏度高、响应时间快等特点,可用于大范围大气有毒有害气体的遥感监测,成为近年来大气有毒有害气体激光遥测技术发展的重点。首先阐述了差分吸收激光雷达大气遥测基本原理,其次从激光器应用和系统平台发展两个方面分析了该技术的技术发展现状,最后提出了宽光谱、多波长、新探测体制的激光雷达、多平台应用、复合系统将成为未来基于差分吸收激光雷达有毒有害气体遥测发展方向。

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%。

对流层低层臭氧的差分吸收激光雷达测量

利用紫外差分吸收(DIAL)激光雷达对北京南郊对流层低层臭氧垂直分布进行了测量,将探测结果与探空气球同时测量的结果进行了对比,取得了较为一致的分布趋势。选择北京南郊地区晴好天气探测的结果进行了统计分析,结果表明:近地面层内随高度增加,臭氧体积混合比逐渐减小;距地面0.5～1.5km内平均臭氧体积混合比具有明显的日变化趋势,最大值出现在午后14点左右,相对太阳辐射最强时刻具有明显的滞后性;日平均最大体积混合比低于4×10-8,体积混合比起伏小于±3.2×10-9。

CO_2差分吸收激光雷达信号处理

针对CO_2差分吸收激光告警雷达系统,研究累加平均和匹配滤波两种算法.将两种方法进行耦合,结合了各自的优点,使得激光雷达在小信噪比下工作,提高了检测距离,计算出较远距离时,化学物质的 CL浓度值.将该方法应用到 CO_2差分吸收激光告警雷达系统中。通过仿真实验,能有效地去掉噪声和强干扰信号,在保持原信号特征的情况下,较准确地提取出有效的弱信号,计算出化学物质的浓度距离,模拟出测量到某种化学物质.

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。

地基CO2廓线探测差分吸收激光雷达

研制了一台利用气溶胶散射信号的CO_2廓线探测差分吸收激光雷达.系统利用染料激光器实现波长调制,采用双光路气体吸收池,结合Voigt拟合方法实现了脉冲红外激光的高精度定标.针对输出激光带宽较宽的问题,采取仿真实验评估了影响,并设计了基于吸收池的订正因子获取方案.进而,开展了水平、垂直和连续观测实验,通过与地面CO_2分析仪测量值的对比,证明了系统具备优越的精密性和精确性.实验表明,该样机能够俘获CO_2浓度随高程和时间变化而产生的变化.

基于参量振荡探测对流层CO_2的差分吸收雷达

设计了一种新颖探测对流层二氧化碳气体的 1572nm 差分吸收雷达,它的发射系统基于脉冲的种子注入 KTP 参量振荡器(OPO)。OPO 由 1064nm Nd:YAG 多模激光泵浦,转换效率 10%,重复频率 20Hz,OPO 的腔长由 PZT 单元和二氧化碳多通道吸收池精确控制,种子注入时,它可以产生单模窄带的信号光脉冲输出, 对应的空闲光输出仍然是多模。窄带 on 光源(线宽小于600MHz)对应于二氧化碳光谱的强吸收线,宽带 off 光源(150GHz)对应于光谱的弱吸收线。on 和off 双波长工作是通过对种子光的 10Hz 开关来得到的。雷达接收系统的核心是近红外光电倍增管和光子计数器,光电倍增管制冷到-60℃以降低其噪声。实验表明,该雷达的信噪比在 6km 以内大于 10 :1(10 分钟 6000 个脉冲累加)。