参数化的多次散射激光雷达方程和它的反演理论 Ⅰ:方程

本文提出了一个参数化的多次散射激光雷达方程,该方程基于本文引出的四个因子,即几何消光因子、消光分布因子、前向散射因子和后向散射因子.前两个因子表征多次散射成分对大气消光系数分布、激光的发散角和接收视场角以及接收孔径的依赖关系,后两个因子表征多次散射成分对散射相函数的依赖关系.这个参数化多次散射雷达方程在241个数值试验中得以检验,这些试验包含很宽的大气条件和雷达几何参数,包括14个大气散射相函数,均匀和不均匀的大气消光系数分布,0.5至1之间变化的一次散射反照率,地基和空间站激光雷达两种情形.数值试验表明,在小于4的光学厚度内参数化的解和Monte-Carlo解之间的标准偏差小于27％,而本模式的计算时间比Monte-Carlo方法偏小4个数量级左右.本模式不仅适合于研究多次散射对激光回波信号和激光大气遥感的效应,而且对于考虑多次散射的激光大气探测而言,是一个合适的应用模式.     

参数化的多次散射激光雷达方程和它的反演理论 I:方程

本文提出了一个参数化的多次散射激光雷达方程,该方程基于本文引出的四个因子,即几何消光因子、消光分布因子、前向散射因子和后向散射因子.前两个因子表征多次散射成分对大气消光系数分布、激光的发散角和接收视场角以及接收孔径的依赖关系,后两个因子表征多次散射成分对散射相函数的依赖关系.这个参数化多次散射雷达方程在241个数值试验中得以检验,这些试验包含很宽的大气条件和雷达几何参数,包括14个大气散射相函数,均匀和不均匀的大气消光系数分布,0.5至1之间变化的一次散射反照率,地基和空间站激光雷达两种情形.数值试验表明     

合肥市郊低层大气的激光雷达探测研究

利用L300米散射激光雷达对合肥市郊大气边界层进行长期系统观测.分析讨论了大气边界层气溶胶消光系数与温度、湿度的关系, 大气边界层气溶胶消光系数垂直分布和时间变化的主要特征, 给出了激光雷达探测的大气边界层高度的统计特征及其与无线电气象探空仪探测大气边界层高度的比较结果.     

气象能见度与望远光度计

本文讨论了在实际工作中用柯什密得能见度公式推算大气消光系数时可能发生的误差。分析表明,由于目标物不是黑体,一般可使消光系数增大10％,但用望远光度计并采取一些适当措施,可把这一误差大大减小.而由于天空云造成光路上大气散射的非均匀性所引起的误差却难于消除.     

齐次积分方程数值求解法及在反演气溶胶谱分布上的应用

本文论述了一个数值求解齐次的第一类Fredholm积分方程的方法,并以消光系数和体积散射系数综合反演气溶胶谱分布为例,说明采用比值通道以反演气溶胶谱分布有利于消除多次散射等系统误差.本文还证明了在Junge谱分布下,不同波长的体积消光系数、散射相函数等Mie散射光学参数之比与折射率无关的特性,指出了采用比值通道能够有效地消除折射率的不确定性对于消光——小角散射法反演气溶胶谱分布的影响.     

能见度与相对湿度的关系

本文通过光散射理论计算,分析了大气消光系数(削弱系数)与相对湿度的关系,并与观测实例进行了比较。由此提出在一定条件下,根据相对湿度的未来变化预报气象能见度的可能性。 气象能见度对交通运输和光学探测等一系列实际问题均具有重要意义,是气象台站的常规观测项目之一。     

成都夏季气溶胶消光特性研究

本文利用成都2017年6~8月的米散射微脉冲激光雷达观测数据,对成都夏季气溶胶消光系数、边界层高度以及气溶胶光学厚度进行了反演,并结合太阳光度计观测资料、地面颗粒物浓度以及大气能见度数据研究了气溶胶消光系数日变化与月变化规律,气溶胶消光系数的垂直分布特征及影响因素。结果表明:气溶胶消光系数的日变化受人类活动以及边界层日变化影响显著,表现出凌晨与傍晚最大,早晨次之,午后最小的特征。消光高值出现在200m以下和300~700m的高度区间,夜间观察到的消光高值可能与颗粒物在夜间近地面浓度较高以及本地夜间降水频发有关。激光雷达反演的消光系数与光度计反演的气溶胶光学厚度在夏季各月的表现一致,夏季各月消光极值均出现在100~150m的近地面层。近地面消光系数与地面颗粒物浓度之间具有较好的正相关,并且粒子粒径更小时相关性更好。气溶胶光学厚度主要来自低层大气的贡献,0.1~0.2μm的细粒子气溶胶占比对于大气消光有主要影响,但气溶胶对大气的消光影响除了与粒子浓度有关,还与粒子的理化性质有关。      

参数化的多次散射雷达方程和它的反演理论 II:反演理论

本文根据参数化的多次散射雷达方程,分析了激光多次散射对激光回波信号和一次散射雷达方程反演结果的效应,提出了迭代前向积分法和迭代后向积分法以求解参数化的多次散射雷达方程,并根据多次散射信号对云和气溶胶的前向散射相函数的高度敏感性提出了一个从双接收视场的多次散射激光回波信号,同时确定云和气溶胶消光系数分布和前向散射相函数的方法.此外,本文还根据数值试验分析了这些反演方法在地基激光雷达和空间站激光雷达两种情形下的适用性.     

参数化的多次散射雷达方程和它的反演理论 Ⅱ:反演理论

本文根据参数化的多次散射雷达方程,分析了激光多次散射对激光回波信号和一次散射雷达方程反演结果的效应,提出了迭代前向积分法和迭代后向积分法以求解参数化的多次散射雷达方程,并根据多次散射信号对云和气溶胶的前向散射相函数的高度敏感性提出了一个从双接收视场的多次散射激光回波信号,同时确定云和气溶胶消光系数分布和前向散射相函数的方法.此外,本文还根据数值试验分析了这些反演方法在地基激光雷达和空间站激光雷达两种情形下的适用性.     

湿气溶胶的光散射特性

在不同干气溶胶谱分布以及激光波长为6943埃的条件下,根据三种湿气溶胶模式,理论计算了湿气溶胶的消光系数和体后向散射微分截面,并分析讨论了它们随相对湿度的变化规律。     

基于腔减相移光谱技术测量大气气溶胶消光系数的应用研究

基于腔减相移光谱(CAPS)技术检测灵敏度高、光源性价比好、容易控制和有效吸收光程长等优点,搭建了一套基于CAPS技术的连续测量大气气溶胶消光系数的监测系统。测试系统高反射镜片反射率约为0.9999,对应有效光程约为4.4 km;通过Allan方差测试分析系统最佳积分时间约为80 s,对应消光系数检测极限为0.06Mm-1;将系统应用于实际大气气溶胶消光系数的12个周期和48 h连续监测,显示空腔相移基本稳定,样品测量相移偏移明显,反演得到的大气能见度结果稳定可靠。由此表明,研制的基于CAPS技术的大气气溶胶消光系数连续测量系统应用于实际的测量是完全可行的。     

Visibility and telephotometer

This paper discusses the possible error of the calculation of the atmospheric extinction coefficient by the Koschinieder visibility formula. An analysis of the problem shows that an error of 10% can be in-troduced in the measurement if the target used is a non-blackbody. By using the telephotometer as a tool of measurement, such an error can be markedly reduced.     

上海市大气颗粒物与能见度的关系

大气能见度成为当前区域大气环境研究的重要指标,不同粒径的颗粒物对能见度的影响有着显著的区别。本研究在线连续监测了上海市嘉定区2008年11月—2009年1月不同粒径大气颗粒物质量浓度和粒子数浓度的日变化,同步收集了相同区域空气水平能见度的数据。比较不同粒径大气颗粒物质量浓度与空气水平能见度和颗粒物消光系数的相关性,结果表明：中值粒径为0.4 μm和0.65 μm的大气颗粒物对上海嘉定空气水平能见度的影响最显著;中值粒径为0.17 μm、0.26 μm、0.40 μm和0.65 μm的大气颗粒物对颗粒物的消光系数影响较大。该相关系数的分布趋势与各种组分(SO42-、NO3-、NH4+、OC和EC)的粒径分布十分一致,证明了这五种组分是影响大气颗粒物消光系数的重要原因。     

A New Method for Aerosol Retrieval Based on Lidar Observations in Beijing

Lidar has been used extensively in the area of atmospheric aerosol measurement. Two unknowns at the reference altitude, the lidar ratio and the backscatter coefficient, need to be resolved from the lidar equation. In the actual application, these two values are difficult to obtain, particularly the backscatter coefficient. To better characterize the optical properties of aerosols, optical thickness, and attenuated backscatter obtained by other instruments are usually used as the input for joint inversion. However, this method is limited by location and time. In this study, the authors propose a new method for aerosol retrieval by using Mie scatter- ing lidar data to solve this problem. The authors take the horizontal aerosol extinction coefficient as the con- straint to begin the iteration until a self-consistent aerosol vertical profile was obtained. By comparing their results with Aerosol Robotic Network （AERONET） data, the authours determine that the aerosol extinction coefficient obtained by combining horizontal and vertical lidar observations is more pre- cise than that obtained by using the traditional Fernald method. This new method has been adopted for re- trieving the extinction coefficient of aerosols during the observation days.     

Perception visual range and sky background

Abstract

The meteorological visual range V_m and the perception visual range V_p have been measured for a variety of horizon sky backgrounds and atmospheric extinction conditions. Comparison with the standard visibility V_n shows that in general V_p > V_m > V_n . Model calculations of V_p, V_m and V_n for different synthetic sky backgrounds and for an extinction coefficient function of the form σ(λ) = k λ^‐α in which a was varied from ‐1 to 4 show that the wavelength of maximum perception can vary between ～540 and ～630 nm. Under typically turbid or polluted atmospheric conditions and for a blue or white sky background the extinction coefficient should be measured at ‐570 nm if prevailing visibility is to be reliably estimated.     

Long‐term variations in the turbidity of the arctic atmosphere in Russia

Abstract

Temporal variations of the transmission coefficient and aerosol optical depth of the atmosphere are considered using multi‐year observations at the Soviet polar stations in the Arctic. The contribution of atmospheric aerosol to the total extinction of solar radiation is estimated. A decreasing trend of atmospheric transparency due to the increase of aerosol contributing to the extinction of solar radiation during the last 25–30 years is noted. Estimates of the atmospheric aerosol influence on the incoming solar radiation indicate that a further systematic decrease of the transmission coefficient may lead to climatic changes of direct and total radiation in most polluted areas of the Arctic.     

MEASUREMENTS OF THE ABSORPTION COEFFICIENT OF ATMOSPHERIC AEROSOLS

This paper discusses the measurement of the absorption coefficient of atmospheric aerosols and its measuring system based on the principle of integrating plate. Measurements in Beijing show that the absorption coefficient of atmospheric aerosols in the heating period varies in a range of 10^-3 to 10^-4 m^-1 and in the non-heating period, its values are near 10^-4m^-1.     

降水现象对大气消光系数和能见度的影响

大气中各种粒子对大气消光系数和能见度有不同程度影响,除气溶胶粒子外,降水粒子对能见度影响也不可忽视。为了解降水粒子对能见度的影响,确定能见度变化与降水现象之间的关系,该文在分析降水粒子的大小、速度、形状、谱分布、光学特性等特征的基础上,忽略气溶胶粒子的影响,建立基于实测谱分布的降水与能见度的理论模型,讨论不同类型降雨、降雪对大气消光系数和能见度的影响。同时选取Parsivel降水粒子谱仪在南京地区的降雨和降雪观测记录,利用实测数据来对比验证本文所建立的降水-能见度理论模型。结果表明:能见度随着降水强度的增大呈指数降低;受降水粒子特性和天气条件等多种因素影响,能见度与降水强度之间的关系并不是唯一对应的;降雨和降雪对能见度的影响各不相同,相比而言,降雨对能见度的影响比较容易确定,而降雪对能见度的影响比较复杂,主要因为雪花或冰晶的类型复杂多变,对大气消光系数有不同程度的影响。结合理论分析和实测数据对比验证,降水现象对能见度的影响得到了证实。     

Integration method and ratio method for retrieving extinction coefficient from lidar signals

New solution techniques to improve the accuracy of quantitatively determining the atmospheric extinction coefficient and the backscattering-to-extinction ratio from lidar signals are developed. The integration method is proposed to analytically retrieve the extinction coefficient at ground level, which has the advantage of eliminating the effect of backscattering fluctuations on the inversion results.The ratio method, on the other hand, deals with the inversion of the vertical distribution of the extinction coefficient. The main idea of this method is to begin with a calculation of the transmittance by eliminating the backscattering through ratioing lidar signals at two elevations, and subsequently derive the extinction coefficient from the transmittance, thus avert from ambiguous results caused by inappropriate assumptions on the backscattering-to-extinction ratio. Observational investigations have demonstrated that the integration method is superior to the slope method in terms of accuracy and stability, and the ratio method is reasonable and feasible as well.