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.     

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.     

全光纤多模速度干涉仪的研究

针对传统全光纤单模速度干涉仪在爆炸冲击试验中,前端的单模准直器对高速运动的物体的漫反射光难以有效收集,提出了全光纤多模速度干涉仪的装置。利用超辐射发光二极管作为光源,初步验证了全光纤多模速度干涉仪的可行性。主要阐述了全光纤多模速度干涉仪的原理和结构,并将其与全光纤单模速度干涉仪在喇叭振动速度的实验中进行比较,取得了一致的结果,最后还进行霍普金森压杆撞击实验,实测的速度最大值为10.49 m/s,与理论值10 m/s符合较好。     

基于三级Fabry-Perot标准具的纯转动拉曼测温激光雷达

提出了新的纯转动拉曼测温雷达系统,即以种子激光注入锁定的Nd:YAG激光器为激发光源,采用基于三级Fabry-Perot(F-P)标准具的双通道分光结构代替双光栅单色仪结构.通过通道中宽带滤光片(带宽为7nm)及F-P标准具的组合使用,对532nm激发光的大气Mie-Rayleigh弹性回波散射抑制比可达10^-10,对量子数J=±6,J=±12的N₂纯转动拉曼散射光谱线接收带宽均小于10pm,因此能充分抑制大气背景辐射噪声及O₂纯转动拉曼谱线的干扰,从而实现了单谱线比反演温度,提高了探测精度,且可在白昼探测大气对流层温度.最后通过探空气球测得的对流层温度垂直分布逆向模拟了该系统双通道的Raman信号曲线,证实了该系统的可行性. 关键词： 拉曼激光雷达 纯转动拉曼散射 三级Fabry-Perot标准具 对流层     

多条转动拉曼谱线雷达测量对流层大气温度

由于对流层大气中气溶胶的存在,传统的利用大气中瑞利散射和振动拉曼散射测量大气温度的方法具有一定的局限性,然而利用大气N₂和O₂分子的的转动拉曼信号获得大气温度信息的方法不受对流层大气中气溶胶的影响。因此利用N₂和O₂分子纯转动拉曼散射激光雷达开展了测量对流层下部温度分布的实验研究。现有的转动拉曼雷达系统基本上是通过获取单一的转动拉曼谱线来反演大气温度,这就导致了系统的信噪比低,不能很好的反演温度。作者在双光栅单色仪的基础上提出了一种新的雷达信号分光系统。这种新的分光系统的每条通道所获得的信号并不是单独的转动拉曼谱线,而是多条转动拉曼谱线之和,这样就能提高整个系统的信噪比。在较小的激光能量和小口径望远镜的情况下,利用这种方法,雷达系统可以在几公里内获得较好的信噪比。最后实验得到了对流层0.3～5 km高度内的大气温度分布, 它与球载无线电探空仪比较, 二者一致性较好。     

转动拉曼激光雷达探测大气温度的系统设计及模拟计算

本文对转动拉曼散射激光雷达探测的大气后向散射回波进行了数值模拟计算,计算结果得到了现有的数据的验证,证明了这种设计是可行的。并就激光脉冲能量、发射的激光脉冲数、望远镜的直径和垂直分辨率对转动拉曼激光雷达回波信号信噪比的影响进行了较为详细的分析与讨论,简要分析了测温精度。     

纯转动拉曼法确定激光雷达几何因子

提出了一种确定激光雷达几何重叠因子的新方法。研究了大气分子纯转动拉曼谱线强度分布特征。利用大气分子总的纯转动拉曼激光雷达信号结合瑞利-米氏散射激光雷达信号能精确反演激光雷达几何因子。这种方法消除了振动拉曼方法中气溶胶波长指数影响以及水平测量法气溶胶非均匀性的限制。数值模拟结果表明:在大气温度三种分布模型和气溶胶波长指数三种分布模型下几何因子反演的最大相对误差小于0.5%。根据实际激光雷达信号反演得到了系统的几何因子。     

利用转动拉曼测量大气气溶胶后项散射比

利用大气的弹性散射信号与整个转动拉曼信号的比值,不需要假设任何的气溶胶的消光与后项散射比值,就可得到大气气溶胶的后项散射比。通常测量部分转动拉曼谱线之和代替全部转动拉曼谱线之和。全部的转动拉曼谱线之和是不依赖温度,但部分的转动拉曼谱线之和却是与温度有关的。因此,利用转动部分拉曼谱线之和反演大气气溶胶的后项散射比就会带来误差。模拟了随温度变化不同转动量子数的拉曼谱线之和,并且计算了由这些不同转动拉曼谱线之和反演大气气溶胶后项散射比的误差。然后文章提出了一种新的方法,不需要测量整个转动拉曼谱线之和,而只需要测量单条转动拉曼谱线及大气温度,就可以获得大气气溶胶的后项散射比。最后通过实验给出了实际测量的大气气溶胶的后项散射比的结果。     

差分吸收测污激光雷达光路分束设计

在AML-2车载测污激光雷达中,对装有不同气体的拉曼管进行拉曼激发获得相应的强、弱吸收关波长。针对差分雷达激光发射光路转换的特点及提高雷达监测的实时性能要求,基于激光偏振调制原理提出了激光雷达光路分束设计的新方法,对该方法可行性进行了理论分析,并对改进光路的能量损失进行了估算,模拟结果显示改进后的系统延长了仪器的使用寿命,提高了测量的实时性。为提高差分激光雷达实时监测性能提供了一种新方法。