合肥地区卷云的激光雷达探测

为了研究卷云的特征,我们利用L300米散射激光雷达对安徽省合肥地区(31.90°N,117.16°E)的高层卷云进行探测.这些卷云是在晴朗夜晚激光雷达进行对流层气溶胶常规测量的同时探测到的.分析讨论了卷云的结构、光学性质及其它们的时间变化特征.结果表明:该地区卷云的云峰主要分布在8～11 km范围之内,卷云的结构呈现一定的季节变化特征.     

星-地激光雷达联合观测合肥地区的气溶胶垂直分布

通过匹配星载CALIOP过境合肥时间,筛选Aerosol-lidar的观测数据,选取4个典型天气个例[沙尘天气、多云天气、中度污染(无云)、中度污染(有云)],对合肥地区的气溶胶进行联合观测,并对气溶胶的类型、气溶胶的变化、气溶胶污染的成因及来源进行分析。结果表明,多云天气下,星载激光雷达对底层气溶胶探测时会受到天气的影响,而地基激光雷达的探测效果较佳,可以通过定点连续观测距离的校正信号准确地反映气溶胶含量和变化特点。星-地激光雷达的联合观测可以更好地分析多种复杂天气的气溶胶变化。联合观测结果表明:轻度污染的沙尘型和受污染的浮尘型气溶胶主要集中在0.8~1.6 km高度范围内,退偏振比集中在0.18~0.20之间;多云天气的气溶胶主要为污染大陆型,集中在0.4~1.2 km高度范围内,其退偏振比在0.015~0.020之间,气溶胶含量很少且为具有球形粒子属性的细颗粒物;中度污染(无云)天气的气溶胶同时包含污染浮尘型和污染大陆型,主要集中在0.3~1.3 km高度范围内,退偏振比在0.08以下,具有明显的球形粒子属性;中度污染(有云)天气的气溶胶也同时包含污染浮尘型和污染大陆型,主要集中在0.8~1.4 km高度范围内,退偏振比在0.075~0.100范围内,为粒径较小的球形粒子。     

喇曼激光雷达探测云及其附近气溶胶光学参量

为了研究喇曼激光雷达探测云与气溶胶相互作用相关光学参量的可行性,研制了一台607nm喇曼激光雷达。采用适当提高喇曼激光雷达配置的方法,提高了喇曼回波信号信噪比。通过实验取得了晴空少云天气下云和气溶胶的消光系数垂直廓线,给出了喇曼激光雷达观测云与气溶胶相互作用的个例分析,说明利用地基喇曼激光雷达,可以为研究云与气溶胶之间相互作用的物理过程提供基础数据,并指出正在研制的多波长喇曼-偏振激光雷达技术探测云与气溶胶相互作用的技术优势。结果表明,喇曼激光雷达具备定量探测中低自由对流层内薄云层和气溶胶消光系数的能力。     

卷云消光后向散射比的激光雷达测量

高层卷云对天气和气候有着重要的影响,其消光后向散射比是它的一个重要光学特性.假设卷云上方和下方没有气溶胶,只有大气分子,由激光雷达信号就可反演出卷云的透过率和光学厚度,进而算出卷云的消光后向散射比.对美国汉普顿大学的532 nm通道激光雷达测量的卷云数据进行了分析,数据采集期间从2007年1月至10月,共选取了光学厚度在0.08～1.5之间的798组卷云数据.计算结果表明:卷云高度主要分布在7～13.5 km之间;卷云消光后向散射比平均值为21.4 sr,月季特征并不很明显,概率分布呈现出正态分布特征;光学厚度的概率分布函数说明大部分为薄卷云.     

Algorithm to Retrieve Aerosol Optical Properties From High-Spectral-Resolution Lidar and Polarization Mie-Scattering Lidar Measurements

We developed an algorithm to estimate the vertical profiles of extinction coefficients at 532 nm for three aerosol types that are water-soluble, soot, and dust particles, using the extinction and backscattering coefficients at 532 nm for total aerosols derived from high-spectral-resolution lidar (HSRL) measurements and the receiving signal at 1064 nm and total depolarization ratio at 532 nm measured with Mie scattering lidar (MSL). The mode radii, standard deviations, and refractive indexes for each aerosol component are prescribed by the optical properties of aerosols and clouds database; the optical properties for each aerosol component are computed from Mie theory on the assumption that their particles are spherical and homogeneous, except for dust. To consider the effect of nonsphericity, the dust lidar ratio at 532 nm is assumed to be 50 sr, the value that is reported for Asian dust from the other observational studies. We performed sensitivity study on retrieval errors. The errors in extinction coefficient for each aerosol component were smaller than 30% and 60% when the measurement errors were $pm$5% and $pm$ 10%. We demonstrated the ability of the algorithm by applying to the $ hbox{HSRL} + hbox{MSL}$ data measured at Tsukuba, Japan. Plumes consisting of water-soluble aerosols, soot, dust, or their mixture were retrieved; these results were consistent with simulation with a global aerosol transport model. Introducing the dust lidar ratio significantly improved a correlation between the retrieved dust concentration and the aerosol depolarization ratio at 532 nm derived from $ hbox{HSRL} + hbox{MSL}$ than the use of spherical dust optical model in the retrieval.      

考虑多次散射的卷云几何特征和光学特性反演方法

研究了考虑多次散射的卷云几何特征和光学特性反演方法,对反演卷云高度和卷云激光雷达比的方法进行了改进。采用多次散射因子对卷云消光系数曲线进行修正,选取云底及云顶附近高度消光系数变化率的均值求解云层高度修正误差,对微分零交叉法求解得到的卷云高度进行修正,实现了较为精确的激光雷达云层高度反演。采用以边界值处消光系数和卷云光学厚度为约束条件的粒子群算法,求解卷云有效激光雷达比,选用半解析Monte Carlo方法,计算总散射信号与一次散射信号的比值,并结合Platt多次散射因子方程求得多次散射因子,实现了卷云激光雷达比的准确求解。使用Mie散射激光雷达真实回波信号进行了验证。结果表明,该改进方法具有较高的精度,更具应用价值。     

Retrievals of profiles of fine and coarse aerosols using lidar and radiometric space measurements

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) spaceborne lidar, expected to be launched in 2004, will collect profiles of the lidar attenuated backscattering coefficients of aerosol and clouds at 0.53 and 1.06 /spl mu/m. The measurements are sensitive to the vertical distribution of aerosols. However, the information is insufficient to be mapped into unique aerosol physical properties and vertical distribution. Spectral radiances measured by the Moderate Resolution Imaging Spectrometer (MODIS) on the Aqua spacecraft, acquired simultaneously with the CALIPSO observations, can constrain the solutions. The combination of the MODIS and CALIPSO data can be used to derive extinction profiles of the fine and coarse modes of the aerosol size distribution for aerosol optical thickness of 0.1 and larger. Here we describe a new inversion method developed to invert simultaneously MODIS and CALIPSO data over glint-free ocean. The method is applied to aircraft lidar and MODIS data collected over a dust storm off the coast of West Africa during the Saharan Dust Experiment (SHADE). The backscattering-to-extinction ratio (BER) (BER=/spl omega//sub o/P(180)/4/spl pi/) can be retrieved from the synergism between measurements avoiding a priori hypotheses required for inverting lidar measurements alone. For dust, the resultant value of BER =0.016 sr/sup -1/ is over 50% smaller than what is expected using Mie theory, but in good agreement with recent results obtained from Raman lidar observations of dust episodes. The inversion is robust in the presence of 10% and 20% noise in the lidar signal at 0.53 and 1.06 /spl mu/m, respectively. Calibration errors of the lidar of 5% to 10% can cause an error in optical thickness of 20% to 40%, respectively, in the tested cases.     

Lidar sensing of aerosols and clouds in the troposphere and stratosphere

Advances in the development and application of lidar as a tool for the remote sensing of atmospheric aerosols and clouds are reviewed. The lidar sensing technique is described, and various approaches for solving the lidar equation to retrieve aerosol properties are summarized. Examples are presented of lidar applications of aerosol and cloud sensing in both the troposphere and stratosphere. These include environmental monitoring, atmospheric boundary layer studies, retrieval of aerosol optical and physical properties, sensing of clouds, and investigation of volcanic effects in the stratosphere. Comments are offered regarding the future outlook for aerosol and cloud sensing by both ground-based and spaceborne lidar.<>     

西北半干旱区激光雷达探测卷云几何特征和光学厚度

为了研究中国西北半干旱区卷云几何特征和光学特性的时空分布特征,我们利用兰州大学半干旱气候与环境观测站（SACOL,35.95°N,104.14°E）的微脉冲激光雷达（MPL-4B）探测卷云过程,分析讨论了卷云的结构、光学性质及其时间变化特征,结果表明,卷云高度分布范围为7－10km,卷云经历了薄－厚－薄的过程,平均厚度为2.0±0.5km。卷云环境温度在－51～－39℃范围之内。卷云的光学厚度在0.084－1.649之间,光学厚度随几何厚度的增加而增大,平均光学厚度为0.651±0.403。多次散射效应对光学厚度大于0.3的卷云影响较大。卷云激光雷达比为17±17sr。薄卷云的激光雷达比要比厚卷云的大。光学厚度小于0.3的光学薄卷云出现高度在8.6km以上,环境温度低于－45℃,几何厚度小于1.5km,雷达比分布在5－69 sr。     

First results from the OMI rotational Raman scattering cloud pressure algorithm

We have developed an algorithm to retrieve scattering cloud pressures and other cloud properties with the Aura Ozone Monitoring Instrument (OMI). The scattering cloud pressure is retrieved using the effects of rotational Raman scattering (RRS). It is defined as the pressure of a Lambertian surface that would produce the observed amount of RRS consistent with the derived reflectivity of that surface. The independent pixel approximation is used in conjunction with the Lambertian-equivalent reflectivity model to provide an effective radiative cloud fraction and scattering pressure in the presence of broken or thin cloud. The derived cloud pressures will enable accurate retrievals of trace gas mixing ratios, including ozone, in the troposphere within and above clouds. We describe details of the algorithm that will be used for the first release of these products. We compare our scattering cloud pressures with cloud-top pressures and other cloud properties from the Aqua Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument. OMI and MODIS are part of the so-called A-train satellites flying in formation within 30 min of each other. Differences between OMI and MODIS are expected because the MODIS observations in the thermal infrared are more sensitive to the cloud top whereas the backscattered photons in the ultraviolet can penetrate deeper into clouds. Radiative transfer calculations are consistent with the observed differences. The OMI cloud pressures are shown to be correlated with the cirrus reflectance. This relationship indicates that OMI can probe through thin or moderately thick cirrus to lower lying water clouds.     

星载大气探测激光雷达探测能力的数值模拟分析

星载大气探测激光雷达的技术参数对其探测性能有重要的影响,本文使用合适的大气模式和星载大气探测激光雷达设计参数,对其接收的大气后向散射回波信号和探测回波信号的信噪比进行了数值模拟计算;同时模拟分析了星载大气探测激光雷达对沙尘和卷云的探测能力。本文结果为该星载大气探测激光雷达的研制提供参数设置的基本依据。     

高层薄卷云消光后向散射比的求解方法

卷云的消光后向散射比是研究卷云光学特性的一个重要参量,我们的工作就是利用米散射激光雷达探测的大气和卷云的后向散射信号来获得间断出现的高层薄卷云的消光后向散射比.在无大的天气系统过境的情况下,通过对定点观测到的雷达上空有卷云和无卷云的大气回波信号的对比求解,得出间歇性卷云的消光后向散射比,并与其他方法进行了对比分析,指明了该方法的可靠性和局限性.     

Spaceborne lidar calibration from cirrus and molecular backscatter returns

In order to make optimal quantitative use of multiwavelength spaceborne lidar data, it is essential that the lidar be well calibrated. Due to system gain/efficiency changes that can be expected to occur during the course of a shuttle or satellite mission, it is essential to employ a calibration approach that can be implemented on-orbit, preferably repeatable at least a few times per orbit. For wavelengths less than about 550 nm, in situ calibration can be accomplished via normalization to high-altitude nearly molecular scattering regions. However, for longer wavelengths beyond about 800 nm, particularly the popular Nd: YAG fundamental wavelength at 1064 nm, the Rayleigh normalization approach becomes questionable due to both an inherently weaker signal and a stronger, variable, and somewhat unknown aerosol scattering contribution. For lidars operating at both longer and shorter wavelengths, a viable approach is to retrieve the longer wavelength calibrations ratioed to the shorter wavelength calibrations via comparisons of spectral backscatter from known/quantifiable scatterers. Cirrus clouds are good for this purpose because they occur at high altitudes with significant frequency and provide strong nearly spectrally flat backscatter. This paper presents both the molecular normalization and cirrus spectral backscatter ratio calibration approaches, including results obtained from case studies of lidar data collected during the LITE shuttle mission. Attention is focused on developing a simple autonomous approach applicable to satellite lidar missions such as Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) and the Geoscience Laser Altimeter System (GLAS).     

测量大气气溶胶和水汽的车载式激光雷达系统

为满足国家对大气参数测量的需求,成功研制了新型车载式大气探测激光雷达系统。该激光雷达主要是通过接收激光与大气中气溶胶粒子和水汽以及氮气分子间的米和拉曼散射信号,结合相应的激光雷达方程,反演出大气水平能见度、垂直气溶胶消光系数和水汽混合比。最终的实际测量结果与对比实验显示,该激光雷达可以对对流层的大气气溶胶进行昼夜连续观测,对夜晚8 km高度范围内以及凌晨和傍晚时分边界层内的水汽进行测量。相应大气水平能见度的测量误差小于20%,而垂直大气气溶胶和水汽的测量误差最大不超过30%。     

典型滤波器对星载高光谱分辨率激光雷达532 nm通道回波信号的影响

高光谱分辨率激光雷达（High Spectral Resolution Lidar,HSRL）系统利用窄带滤波器将激光雷达回波信号中的大气粒子（云或气溶胶）散射和分子散射成分分开,提升了云或气溶胶光学特性的反演质量。提出了一种基于HSRL探测原理的HSRL回波信号模拟方法,其原理是利用CALIPSO云/气溶胶消光系数产品和数值天气预报数据被用来仿真星载HSRL 532 nm回波信号。两种典型的窄带光谱滤波器:FPI（Fabry-Prot Interferometer）和碘吸收滤波器,作为分子通道滤波器的性能通过仿真的星载HSRL回波信号进行分析。对三种典型:晴空、卷云、气溶胶（两层厚云）的HSRL回波廓线进行详细的敏感分析表明碘分子吸收滤波器的性能明显优于FPI滤波器,其中碘吸收滤波能保持可以忽略不计的相对偏差（4.010-3%）,这是由低光学厚度（1.0）的粒子后向散射效应引起的。但是,如果FPI滤波器的粒子后向散射透过率能保持在10-3水平以下,其仍不失为是一个好的选择。     

1.064μm波长卷云反射率的模拟研究

为了给激光测距、激光对大气的探测等实际工程应用提供理论依据,采用逐线积分方法计算大气分子吸收,结合离散纵标法,并耦合卷云的单次散射特性,对由实心六棱柱状冰晶粒子组成的卷云在波长为1.064μm时的散射特性和辐射特性进行了理论分析,得到了该波长上激光在卷云中传输时的反射率随入射光源的位置、观测器的位置以及卷云参量(云光学厚度、粒子尺度等)的关系。结果表明,卷云在1.064μm附近对激光的主要影响是散射,吸收在消光中占了很小的部分;其次,卷云的散射明显改变了光辐射的空间分布,散射的方向变化主要由卷云的散射相函数以及光线入射角度和观测角度决定。这一结果对实际工程应用(比如激光测距、激光对大气的探测等)是有帮助的。     

探测气溶胶-水汽的拉曼-米散射激光雷达系统

设计和构建了发射波长为355 nm和532 nm的户外型全天时激光雷达系统,用于探测大气气溶胶和水汽。运用355 nm和532 nm的米散射、532 nm的偏振、氮气和水汽分子的拉曼激光雷达技术,用于对边界层结构、对流层气溶胶和云光学特性及其形态、水汽混合比进行连续探测研究。该系统结构紧凑,运输方便,具备远程操作、数据传输、一键式启动等功能。利用该系统对大气气溶胶和水汽进行探测,探测结果表明：在大气气溶胶的探测过程中,在重污染条件下混合层高度较干净天低,在0.5 km以下,而干净天在1 km左右;通过对消光系数、Angstrom指数和退偏振比分析可知,重污染条件下,底层大气气溶胶以球形粗粒子污染物为主,干净天底层大气气溶胶以球形细粒子污染物为主;在云层中,Angstrom指数明显减小,且出现负值,说明云粒子半径较大。在水汽探测过程中,采用自标定方法获得系统的标定常数为121,与已标定的激光雷达系统对比,误差在±0.3 g/kg以内;连续探测结果表明可对夜晚5 km及白天混合层以内进行探测。该系统满足产品化的需求,可广泛运用于大气环境的监测领域中。     

典型类型气溶胶散射特性的计算分析

利用云和气溶胶粒子光学特性软件包,对陆地型、海洋型和极地型三种、九类典型气溶胶粒子的散射光学特性进行了数值分析,对比分析了每种类型不同成分对气溶胶粒子体系散射特性的影响,建立了气溶胶散射光学厚度与激光波长、相对湿度的定标关系。对不同类型的气溶胶,气溶胶散射光学厚度随波长的幂指数衰减规律适用范围不同;成分的差异对气溶胶散射光学厚度随波长和相对湿度的变化规律影响较大。根据建立的气溶胶散射光学厚度与波长、相对湿度的定标规律,可为研究非均匀气溶胶粒子体系等效光学特性和激光工程应用提供参考和依据。     

云的多次散射对激光雷达测量结果影响的研究

为了更加准确地获得大气消光系数和后向散射系数,利用半解析Monte Carlo方法对云的大气多次散射激光雷达回波信号进行了模拟计算。分析了激光雷达接收视场角及光学厚度对多次散射回波信号的影响及水云和卷云多次散射因子与光学厚度的关系。激光雷达测量数据的对比结果表明,多次散射对卷云和水云消光系数影响较明显,而对后向散射系数的影响可以忽略。     

激光雷达测量大气气溶胶光学厚度方法研究

介绍一种激光雷达常数标定和气溶胶光学厚度(AOD)测量的新方法.利用太阳辐射计,获得大气气溶胶的光学厚度,激光雷达可以获得35～40 km高度的回波信号,在这一高度区间可忽略气溶胶的存在,大气模式可以提供大气分子散射系数,根据激光雷达方程计算出激光雷达常数.反之,标定激光雷达常数后,根据激光雷达方程,以激光雷达35～40 km的大气分子后向散射回波信号来确定气溶胶的光学厚度.激光雷达测量结果与太阳辐射计的测量结果一致性较好,说明该方法是可行的.这种新方法既可以用于白天的气溶胶光学厚度测量,也可以用于夜间测量.