Measurement of water cloud particle size with a dual-polarization pulsed bistatic lidar

A new bistatic lidar was developed for measuring water cloud particle size at the base of lower clouds. The lidar uses a pulsed Nd:YAG laser at 532 nm and a receiver having a polarization analyzer located at a suitable scattering angle. Cloud particle size (mode radius of the assumed size distribution) was derived from the ratio of the polarization components of the scattered light based on the single scattering Mie theory. The experiment was performed on board the research vessel Mirai in the northwestern Pacific. Particle size at the bottom of maritime cumulus and stratus was measured, and the difference between the internal structures of cumulus and stratus was observed. The effect of multiple scattering was studied by changing the observing scattering angle. The effect was not significant when the penetration depth was less than 50 m.     

基于激光雷达和毫米波云雷达的卷云特性分析

使用美国ARM计划安徽省寿县站2008年的微脉冲激光雷达和毫米波雷达的观测数据对寿县上空卷云的宏观物理特性进行了分析,联合两种雷达观测卷云扩大了卷云的边界轮廓,得到更为全面的卷云信息,结果表明了联合激光雷达和毫米波雷达观测卷云的必要性。在此基础上,对观测期间寿县上空的卷云个例进行统计分析,结果显示：卷云过程的平均云底高度分布在5~10 km,其中6~7 km范围所占的频率最大;平均云厚的分布范围为0.25~5 km,其中90.8%分布在0.5~2.5 km;卷云过程持续时间总体上随着持续时间的增大呈减少的趋势,持续时间最长为35.5 h,平均为3.6 h,持续时间小于5 h的卷云过程占82.5%。     

On the retrieval of ice cloud particle shapes from POLDER measurements

Shapes of ice crystals can significantly affect the radiative transfer in ice clouds. The angular distribution of the polarized reflectance over ice clouds strongly depends on ice crystal shapes. Although the angular-distribution features of the total or polarized reflectance over ice clouds imply a possibility of retrieving ice cloud particle shapes by use of remote sensing data, the accuracy of the retrieval must be evaluated. In this study, a technique that applies single ice crystal habit and multidirectional polarized radiance to retrieve ice cloud particle shapes is assessed. Our sensitivity studies show that the retrieved particle shapes from this algorithm can be considered good approximations to those in actual clouds in calculation of the phase matrix elements. However, this algorithm can only work well under the following conditions: (1) the retrievable must be overcast and thick ice cloud pixels, (2) the particles in the cloud must be randomly oriented, (3) the particle shapes and size distributions used in the lookup tables must be representative, and (4) the multi-angle polarized measurements must be accurate and sufficient to identify ice cloud pixels of randomly oriented particles. In practice, these conditions will exclude most of the measured cloud pixels. Additionally, because the polarized measurements are only sensitive to the upper cloud part not deeper than an optical thickness of 4, the retrieved particle shapes with the polarized radiance may only approximate those in the upper parts of the clouds. In other words, for thicker clouds with vertical inhomogeneity in particle shapes, these retrieved particle shapes cannot represent those of whole clouds. More robust algorithm is needed in accurate retrieval of ice cloud particle shapes.     

基于粒子谱的多波长激光雷达近场大气光学参数校正方法

非同轴激光雷达由于存在发射激光与接收望远镜之间的不完全重叠区, 造成近场回波信号与真实大气信号不一致. 对于多波长激光雷达, 这种不一致更为突出和复杂. 然而, 近场大气是人类活动最集中的区域, 因此对多波长激光雷达近场信号进行校正, 对于了解和探究边界层大气具有十分重要的意义. 提出了一种利用粒子谱仪测量近地层气溶胶尺度谱分布并运用Mie 散射理论和低层大气指数衰减规律, 进而直接校正多波长激光雷达消光系数廓线近场信号的新方法. 通过对晴天、多云天气和雾天多波长气溶胶消光系数廓线近场信号的校正, 证明了该方法的可行性和实用性. 该方法着重考虑了多波长激光雷达比的波长依赖性和气溶胶粒子谱分布的天气相关性, 将该方法用于近地层大气消光系数廓线校正, 减少了由于不考虑这两个因素带来的消光系数廓线反演和校正的不确定性. 该方法对于研究不同天气情况下边界层内的大气气溶胶物理、光学特性具有一定的实用价值和借鉴意义.     

多波长激光雷达探测多种天气气溶胶光学特性与分析

设计和构建了波长为355,532和1064nm的多波长米散射激光雷达系统,并研究了多波长激光雷达信号数据处理和反演算法,实现了对地表气溶胶的探测;利用该激光雷达对2013年冬季西安市上空大气进行了探测,研究分析了雾霾天、晴天和有云天气的混合层高度、气溶胶消光特征和粒径分布特征.分析比较了不同波长探测到的混合层高度变化情况.在雾霾天,大气混合层高度与晴天和有云天相比明显偏低,在0.4 km附近,而晴天的混合层高度有0.5—0.8 km.利用长波(1064 nm/532 nm)段和短波(532 nm/355 nm)段两个ngstrm指数分析了不同天气情况下的粒径分布特征.对于近地层气溶胶,雾霾天的长波ngstrm(1064/532)指数小于短波ngstrm(532/355)指数,而晴天与之相反,说明在近地层雾霾有污染的大气中,存在有较多的粗粒子.在云层中,ngstrm指数明显减小,并且出现负值,说明云粒子半径比较大.     

青藏高原对流层气溶胶的激光雷达监测与研究

运用激光雷达方程和Fernald方法,对西藏那曲地区和北京地区对流层气溶胶的微脉冲激光雷达(MPL)探测数据进行时空反演和比较,结果表明:气溶胶散射比廓线有着较为相似的结构分布,分层锯齿结构非常明显,主要包括贴地层、气溶胶混合层和气溶胶对流层。那曲测站上空气溶胶散射比在无云条件下最大值基本上保持在2.0左右;在测站上空均存在密度较大且较厚的积云;夏季的混合层或残留层(浅蓝色部分)高度抬高;夏季对流层低层积云的云量和积云出现的概率较冬季要少。     

激光雷达监测工业污染源颗粒物输送通量

PM10指能进入呼吸道的质量中值直径小于等于10μm的颗粒物,它是反应环境质量的重要指标,大气中过多的PM10会严重危害身体健康。激光雷达可以测量大气颗粒物消光系数,近地面颗粒物消光系数与颗粒物质量浓度是相关的,利用震荡天平(TEOM)测量近地面的PM10质量浓度,与雷达测量的消光系数建立经验关系,可以推算PM10质量浓度的垂直分布。风廓线雷达可以获得不同高度上的风向风速,将PM10质量浓度与风场数据二者结合可以计算不同高度上颗粒物向城区的输送通量,最终可以估算污染源向城区的输送总量。使用激光雷达技术对北京重要工业污染源进行了长时间的连续监测,获取了颗粒物输送通量等多种参数,给出了连续监测结果。     

一种无需定标的地基激光雷达气溶胶消光系数精确反演方法

如何对低云下雾霾的激光雷达探测数据进行准确定标,一直是米散射激光雷达数据反演中一个有待解决的问题.对于低云和雾霾同时出现的天气,激光很难穿透云层,不能利用大气清洁层对激光雷达信号定标.而对于探测高度小于6 km的便携式米散射激光雷达,由于探测高度较低,也很难利用大气清洁层对激光雷达数据进行定标.本文根据Fernald前向积分方程的特点,提出了一种气溶胶消光系数迭代算法.通过对反演过程进行特定设置,每经过一次迭代,利用气溶胶消光系数迭代算法得到的气溶胶消光系数反演值与其真实值之间的差值就会相应减小.经过几次迭代后,气溶胶消光系数反演值与真实值之间的差值就会小到可以忽略不计.初步反演结果表明:利用气溶胶消光系数迭代算法,无需对激光雷达探测数据定标就能精确反演出气溶胶消光系数廓线.     

Iteration method for the inversion of simulated multiwavelength lidar signals to determine aerosol size distribution

A new method is proposed to derive the size distribution of aerosol from the simulated multiwavelength lidar extinction coefficients. The basis for this iteration is to consider the extinction efficiency factor of particles as a set of weighting function covering the entire radius region of a distribution. The weighting functions are calculated exactly from Mie theory. This method extends the inversion region by subtracting some extinction coefficient. The radius range of simulated size distribution is 0.1－10.0μm, the inversion radius range is 0.1－2.0μm, but the inverted size distributions are in good agreement with the simulated one.     

New particle searches and discoveries: A supplement to the 1976 edition of “review of particle properties”

This supplement to the 1976 edition of “Review of particle properties”, Particle Data Group [Rev. Mod. Phys. 48, No. 2, Part II (1976)], contains tabulations of experimental data bearing on the “new particles” and related topics; categories covered include charmed particles, ψ's and their decay products, and heavy leptons. Errata to the previous edition are also given.     

Comparison of CALIPSO and ground-based lidar profiles over Chung-Li, Taiwan

We report the first inter-comparison of vertical profiles of aerosols and clouds derived from space (CALIPSO) and ground based lidar over Chung-Li, Taiwan. Results show that inter-comparison is closer in case of aerosols than clouds. The strength/shortcoming of the comparison has been also discussed. An iterative calculation to retrieve extinction-to-backscatter ratio (lidar ratio) by using sun-photometer and CALIPSO data is also documented. By using the mentioned method, a mean lidar ratio of 23.5±8.2 sr was found. The derived lidar ratios are lower than former studies. The possible reasons for the difference have been discussed in this paper. The discussed methodology will be helpful to reduce the uncertainty of optical parameters derived from lidar data especially near the surface where the atmosphere is inhomogeneous.     

Fernald前向积分用于机载激光雷达气溶胶后向散射系数反演的理论研究

初步反演结果表明,Fernald前向积分法(FFIM)能够用于机载大气探测激光雷达气溶胶后向散射系数的反演,但相应的理论解释没见国内外相关文献报道.根据合肥地基大气探测激光雷达2008年2月27日的探测数据模拟得到的机载激光雷达数据,对FFIE用于机载大气探测激光雷达气溶胶后向散射系数的反演结果进行了定量分析,分析表明:当反演标定点的高度选在10 km左右时,FFIM能够用于机载大气探测激光雷达气溶胶后向散射系数反演的主要原因有3个:1)Fernald前向积分方程(FFIE)分母中两项的差值一般远大于零, 关键词： 大气光学 Fernald前向积分法 机载大气探测激光雷达 气溶胶后向散射系数     

Optical particle spectrometry—Problems and prospects

Optical particle counters and spectrometers have found broad use in aerosol and atmospheric research, air pollution studies and industrial particle monitoring. The utilization of the elastic scattering of light results in increasingly portable and cost effective instrumentation due to the ongoing miniaturization of building components such as light sources and detectors. However, the non-monotonic size dependence of scattered light intensity and its variability with the changing refractive index of particles influences the function of most single optical particle counters and spectrometers. This problem is a key issue still driving the development of these instruments, first introduced more than half a century ago. Ongoing progress has resulted in not only smaller but also more sophisticated and precise instruments, but the old weakness still remains—varying response to changes of the index of refraction of particles and non-monotonic response curves. Consequently, alternative approaches exploiting elastic scattering are presented here.     

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.     

高光谱分辨率激光雷达鉴频器的设计与分析

提出了利用Fabry-Perot干涉仪的反射场实现高光谱分辨率激光雷达精细探测大气光学参量的新方法和思路.设计了高光谱分辨率的分光系统,并分析了干涉仪反射场的光谱透过特征曲线.结合高光谱激光雷达探测信号特征,讨论分析了谱分离比和瑞利信号透过率随反射率和腔长的变化曲线,同时结合误差传递公式,建立了仿真分析模型,讨论了回波光束发散角和入射角变化对激光雷达探测结果的影响.结果表明,所提出的Fabry-Perot干涉仪反射场可以实现高光谱分辨率激光雷达探测系统的精细分光,同时探测结果误差随回波光束发散角变化不敏感,控制发散角在10 mrad以内,入射角在1.5 mrad以内时,可以实现气溶胶光学参数廓线的高精度探测.     

A review of optical measurements at the aerosol and cloud chamber AIDA

This paper provides a survey of recent studies on the optical properties of aerosol and cloud particles that have been conducted at the AIDA facility of Forschungszentrum Karlsruhe (Aerosol Interactions and Dynamics in the Atmosphere). Reflecting the broad accessible temperature range of the AIDA chamber which extends from ambient temperature down to 183 K, the investigations feature a broad diversity of research topics, such as the wavelength-dependence of the specific absorption cross sections of soot and mineral dust aerosols at room temperature, depolarization and infrared extinction measurements of ice crystal clouds generated at temperatures below 235 K, and the optical properties of polar stratospheric cloud constituents whose formation was studied in chamber experiments at temperatures well below 200 K. After reviewing the AIDA research activity of the past decade and introducing the optical instrumentation of the AIDA facility, this paper presents illustrative examples of ongoing and already published work on optical measurements of soot aerosols, mineral dust particles, and ice crystal clouds.     

Improved method to retrieve aerosol optical properties from combined elastic backscatter and Raman lidar data

Two methods to load a microtrap consisting of two concentric microwire loops of radii 300 and 660 μm carrying oppositely oriented currents are demonstrated. Atoms can be directly loaded into the microtrap from a surface magneto-optical trap or alternatively using a far-off resonance optical dipole trap (FORT) as an intermediate step. About 1 × 10^{5 87}Rb atoms can be loaded into the microtrap using either technique although the FORT achieves a lower temperature. The FORT is well suited to loading a linear array of 3 microtraps that are aligned with the propagation direction of the infrared laser. Atoms can be trapped in either the $5S_{1/2}\;F=1$ or 2 ground state hyperfine level. The position of the microtrapped atom cloud can be precisely adjusted using a bias magnetic field over a distance of 350 to slightly <50 μm from the atom chip surface.     

Influence of particle orientation on retrieving cirrus cloud properties by use of total and polarized reflectances from satellite measurements

The influence of ice crystal orientation was investigated on retrieving cirrus optical thickness (τ) and aspect ratio of ice crystals (Q) from satellite measurements using the total and polarized reflectances at a wavelength of . We considered columnar and plate like hexagonal ice crystals whose long axes are randomly oriented in the horizontal plane (2D model) with some amplitude of oscillation expressed by a Gaussian distribution function with the standard deviation of σ.The retrieved τ and Q values significantly depend on the assumption of σ, in particular for the plate type. Furthermore, the relationship between σ and the retrieved values depends on the solar, satellite, and target geometries. In our case study, for one target area, τ value retrieved using the 2D model with σ=5° was approximately twice larger than that using the 2D model with σ=20°, while the retrieved Q value was not significantly influenced by σ. For another target area, the τ(Q) retrieved using the 2D model with σ=5° was about 1.5 (1.8) times larger than that retrieved using the 2D model with σ=20°.     

An algorithm to determine cirrus properties from analysis of multiple-scattering influence on lidar signals

A Monte Carlo-based evaluation of the multiple-scattering influence on ground-based Raman lidar measurements is presented. The lidar returns from cirrus clouds are analyzed in order to evaluate vertical profiles of the extinction and backscattering coefficients. Results show that for the typical cirrus cloud, the presence of the multiple scattering can lead to an underestimation of the extinction coefficient by as large as 200% whereas the backscattering coefficient is almost unaffected for the Raman lidar technique. An algorithm to select one or a set of phase functions which fit to the lidar data is also presented. It is an iterative procedure based on Monte Carlo scattering simulation. By comparison of the experimental value of the lidar ratio, corrected for the multiple scattering influence, and the phase function used in the Monte Carlo simulation, one can determine a suitable phase function. The validity and sensitivity of the algorithm have been demonstrated by applying it to simulated cases. The application to some real cases indicates that our procedure allows for the establishing of a practical scattering model for the cirrus clouds.     

利用近前向散射图样识别单粒子形状的理论研究

近前向光学散射图样可以用来表征颗粒物的形状.基于球形芽孢杆菌、枯草芽孢杆菌、类鼻疽伯克氏菌的回转长椭球模型, 采用离散偶极子近似方法, 通过模拟3个不同方位探测器接收的散射光强响应信号, 讨论了非球形生物气溶胶颗粒的形状对前向角分辨光强的影响.结合球形指数反演算法, 在一定取向条件下, 前向5°–20° 内角分辨散射光强具有识别长形颗粒物和非长形颗粒物的能力.该研究可以为颗粒物形态测量仪器设计以及快速检测有害生物气溶胶提供依据.