沙尘和灰霾天气下毛乌素沙漠地区大气气溶胶的光学特征

利用AERONET榆林站点的数据比较分析了在沙尘和灰霾两种不同天气条件下毛乌素沙漠边缘地区大气气溶胶的光学和物理特性。分析的主要内容包括:气溶胶光学厚度、单次散射反照率、复折射指数、不对称因子、气溶胶粒子的粒度分布、Angstrom波长指数、体积浓度、气溶胶粒子半径等光学和物理参数。分析结果表明,榆林地区大气气溶胶光学特性主要是受到沙尘和人为气溶胶的共同影响。在沙尘天气和灰霾天气下,大气气溶胶的光学特性有显著的差异。     

沙尘和灰霾天气下毛乌素沙漠地区大气气溶胶的光学特征

利用AERONET榆林站点的数据比较分析了在沙尘和灰霾两种不同天气条件下毛乌素沙漠边缘地区大气气溶胶的光学和物理特性.分析的主要内容包括:气溶胶光学厚度、单次散射反照率、复折射指数、不对称因子、气溶胶粒子的粒度分布、Angstrom波长指数、体积浓度、气溶胶粒子半径等光学和物理参数.分析结果表明,榆林地区大气气溶胶光学特性主要是受到沙尘和人为气溶胶的共同影响.在沙尘天气和灰霾天气下,大气气溶胶的光学特性有显著的差异.     

空气动力学粒径的光学修正

针对空气动力学粒径和光学等效粒径之间存在的差异,本文提出对空气动力学粒径进行光学修正的方法.该方法根据黑碳仪(AE)、浊度计(IN)和光学粒子计数器(OPC)的测量结果,对气溶胶折射率进行反演,再利用反演的折射率结合黑碳仪和浊度计的测量结果对厦门地区空气动力学粒度仪(3321)测量的空气动力学粒径数据进行光学修正,与光学粒子计数器测量结果对比表明修正的结果是合理的.最后还对引起空气动力学粒径和光学等效粒径之间差异的原因进行了分析.     

太阳光谱仪的定标技术与渤海海域的光学测量

本文以太阳光谱仪为基础介绍了根据仪器测量的电信号数据反演气溶胶光学厚度的基本原理以及依据Langley方法的定标技术。通过两次测量试验对比,提出了一种比较实用的仪器定标方法,即在海洋上空对仪器进行定标并且取得了满意的结果。利用该仪器于2003年8月对渤海海域上空的大气光学特性进行了大面积调查,分析了当时海域上空各种大气参数(气溶胶光学厚度、臭氧浓度以及水汽含量等)的空间分布情况,为我国近海海域二类水体水色遥感反演中大气校正模式的建立提供了必要的数据参考。     

气溶胶对远红外激光辐射的衰减规律研究

计算分析了10.6μm波长远红外激光辐射在不同能见度条件下的大气气溶胶中水平传输的衰减系数、有效传输距离以及斜程传输时的透过率变化规律,对比分析了远红外激光辐射在1.0g/m3的高浓度酸雾和油雾气溶胶中的传输能力。根据Mie理论计算了直径为0.5～40μm的水溶性大气气溶胶和尘状气溶胶粒子对10.6μm激光的散射效率因子、吸收效率因子和消光效率因子。结果表明:气溶胶的消光系数越大、大气能见度越低,大气气溶胶对远红外激光辐射的衰减越严重;在1.0g/m3的高浓度酸雾和油雾气溶胶中远红外激光辐射的有效传输距离只有20～50m。水溶性大气气溶胶和尘状气溶胶粒子对10.6μm激光辐射的衰减机理基本相同,其中散射作用居于主导地位并且平均直径大于5μm的气溶胶粒子对10.6μm远红外激光辐射具有显著的衰减作用。     

激光粒子计数器校准中气溶胶稀释方法的研究

为了解决无法通过直接比较法实现激光粒子计数器对凝结核粒子计数器的溯源问题,根据伯努利气体流动原理和气溶胶稀释比例的计算方法,分析了气溶胶在稀释过程中,存在随着补充气体流量的增加,稀释器腔体内压力不恒定的问题,提出了一种新的气溶胶稀释方法,可满足激光粒子计数的溯源问题。实验结果表明,该方法解决了补充气体对气溶胶出气口流量的干扰问题,同时能够对高浓度气溶胶中不同粒径的0～90倍范围内稀释比例保持较好的一致性,测量数据与理论计算值的最大相对误差不超过4.4%。     

光学高分子材料折射率的计算及应用

折射率是光学高分子材料的一项基本性能。本文用 5种方法计算高分子材料的折射率 ,计算结果与测量值一致。几种方法相互结合可以推导出某种方法中未知基团或化学键的折射度值 ,从而计算出该化合物的折射率。利用以上方法对氟化丙烯酸酯聚合物折射率、密度进行了计算 ,计算结果非常准确 ,为光学材料研究提供了新的理论数据     

气溶胶稀释器的稀释比校准方法

选用气溶胶光度计法、光学粒子计数器法和流量测定法对气溶胶稀释器的稀释比进行校准。描述了三种校准方法的校准过程和校准数据,并进行分析、比较,给出了三种校准方法的优劣和适用性,以及在气溶胶稀释器稀释比校准工作的注意事项。     

气溶胶光热干涉测量系统激发参数研究

气溶胶吸收直接影响光在大气中的传播造成光的衰减。本文采用折返式Jamin偏振干涉结构建立了气溶胶光热干涉实验系统,提出并实验研究了在激光照射(加热)和降温两个阶段分别测量吸收系数的方法,确定了两种方法测量气溶胶吸收系数的激发激光功率,为进一步开展气溶胶吸收系数的实验研究提供了参数支持。     

卫星遥感气溶胶光学厚度的双通道方法

本文提出了一种利用ＮＯＡＡ－１４极轨卫星甚高分辨率辐射计可见光和近红外两个通道的反射率资料遥感晴空条件下，均匀下垫面上整层大气气溶胶光学厚度的双通道方法。该方法利用气溶胶散射的波长关系，把基于大气辐射传输方程近红外通道的光学厚度均值引入可见通道，使单个通道中地表反射率和大气因子参数化的误差得以抵消，极大地提高遥感精度。     

High-efficiency aerosol scatterometer that uses an integrating sphere for the calibration of multiwavelength lidar data

For the purpose of calibrating multiwavelength lidar data, we developed a scatterometer to measure the aerosol scattering coefficient at the ground level. The system is based on an integrating sphere, cw lasers (532 and 633 nm), and a controlled flow of the ambient air, including aerosol particles. The simulation study and experimental results indicate that the detection efficiency of this instrument is approximately 10%-40% better than that of an integrating nephelometer, because of the wider acceptance angle of the scattered light. The scattering coefficients measured at the two wavelengths, as well as the resulting value of the angstrom exponent, show good correlation with the results simultaneously measured with an integrating nephelometer and an optical particle counter.     

地面气溶胶集成观测系统

介绍一种地面气溶胶集成观测系统的设计思路和集成方法,采用浊度仪、吸收光度计、粒子计数器、粒径谱仪、碳黑仪等仪器观测气溶胶的散射和吸收特性、黑碳浓度、粒径分布和粒子数浓度等。结果表明,测量吸收特性和粒子数浓度的仪器位于测量散射特性的仪器之后,仪器之间可以互相对比验证;将测量气溶胶吸收特性的仪器和黑碳仪"并联",可以观测到更多气溶胶特性信息;测量气溶胶粒径分布及粒子数浓度的仪器可以结合使用,也可以单独分开或"并联"综合观测;仪器综合集成观测的前提是保证仪器流量分配正确,切割头流量达到要求的范围,保证切割效率。     

High spectral resolution lidar to measure optical scattering properties of atmospheric aerosols. 2: calibration and data analysis

The high spectral resolution lidar (HSRL) measures optical properties of atmospheric aerosols by interferometrically separating the elastic aerosol backscatter from the Doppler broadened molecular contribution. Calibration and data analysis procedures developed for the HSRL are described. Data obtained during flight evaluation testing of the HSRL system are presented with estimates of uncertainties due to instrument calibration. HSRL measurements of the aerosol scattering cross section are compared with in situ integrating nephelometer measurements.     

Case study of modeled aerosol optical properties during the SAFARI 2000 campaign

We present modeled aerosol optical properties (single scattering albedo, asymmetry parameter, and lidar ratio) in two layers with different aerosol loadings and particle sizes, observed during the Southern African Regional Science Initiative 2,000 (SAFARI 2,000) campaign. The optical properties were calculated from aerosol size distributions retrieved from aerosol layer optical thickness spectra, measured using the NASA Ames airborne tracking 14-channel sunphotometer (AATS-14) and the refractive index based on the available information on aerosol chemical composition. The study focuses on sensitivity of modeled optical properties in the 0.3-1.5 microm wavelength range to assumptions regarding the mixing scenario. We considered two models for the mixture of absorbing and nonabsorbing aerosol components commonly used to model optical properties of biomass burning aerosol: a layered sphere with absorbing core and nonabsorbing shell and the Maxwell-Garnett effective medium model. In addition, comparisons of modeled optical properties with the measurements are discussed. We also estimated the radiative effect of the difference in aerosol absorption implied by the large difference between the single scattering albedo values (approximately 0.1 at midvisible wavelengths) obtained from different measurement methods for the case with a high amount of biomass burning particles. For that purpose, the volume fraction of black carbon was varied to obtain a range of single scattering albedo values (0.81-0.91 at lambda=0.50 microm). The difference in absorption resulted in a significant difference in the instantaneous radiative forcing at the surface and the top of the atmosphere (TOA) and can result in a change of the sign of the aerosol forcing at TOA from negative to positive.     

Lidar system model for use with path obscurants and experimental validation

When lidar pulses travel through a short path that includes a relatively high concentration of aerosols, scattering phenomena can alter the power and temporal properties of the pulses significantly, causing undesirable effects in the received pulse. In many applications the design of the lidar transmitter and receiver must consider adverse environmental aerosol conditions to ensure the desired performance. We present an analytical model of lidar system operation when the optical path includes aerosols for use in support of instrument design, simulations, and system evaluation. The model considers an optical path terminated with a solid object, although it can also be applied, with minor modifications, to cases where the expected backscatter occurs from nonsolid objects. The optical path aerosols are characterized by their attenuation and backscatter coefficients derived by the Mie theory from the concentration and particle size distribution of the aerosol. Other inputs include the lidar system parameters and instrument response function, and the model output is the time-resolved received pulse. The model is demonstrated and experimentally validated with military fog oil smoke for short ranges (several meters). The results are obtained with a lidar system operating at a wavelength of 0.905 microm within and outside the aerosol. The model goodness of fit is evaluated using the statistical coefficient of determination whose value ranged from 0.88 to 0.99 in this study.     

Tropospheric aerosol optical properties derived from lidar, sun photometer, and optical particle counter measurements

Tropospheric aerosols have been observed for the period from November 1990 to April 1992 with a lidar, a sun photometer, and an optical particle counter. Variations of aerosol optical thickness derived from the lidar and the sun photometer data and measurements are presented. The simultaneous measurements of these instruments also allowed us to estimate the extinction-to-backscatter ratio (S(1)), which ranged from 20 to 70. Comparison of optical thicknesses derived from both instruments clearly shows the effect of Mt. Pinatubo's eruption and the temporal variation of optical thickness in the stratosphere over 12 km. The possible range of the complex refractive index for the columnar mean aerosols can be deduced from the probable range of S(1) derived by the use of an S(1) diagram as a function of complex refractive index (m). The imaginary part of m can be estimated provided that the real part of m is known.     

CARBONACEOUS AEROSOLS-SINGLE SCATTERING ALBEDO AND EFFECT ON WEATHER HEATING

An experimental setup for the measurement of single scattering albedo of aerosol particles was described. The setup consisted of a nephelometer to measure aerosol light scattering coefficient, a photoacoustic spectrometer to measure aerosol light absorption coefficient, a Single Particle Aerodynamic Relaxation Time (SPART) Analyzer to measure aerosol aerodynamic size distribution, and an aethalometer to measure aerosol mass concentration. Simultaneous measurements of these parameters of a test carbonaceous aerosol were used to determine its single scattering albedo.

At the other hand, a theoretical model based on a “two-stream approximation” was developed and used to calculate the effect of an atmospheric aerosol layer on either global or regional weather heating. It appears that carbonaceous particles in atmosphere may contribute to global temperature rise.

Finally a method of measuring single scattering albedo of single particle by the use of an electrodynamic trap was suggested for studying the effect of different physical states and shapes of particles.     

Determination of polar stratospheric cloud particle refractive indices by use of in situ optical measurements and T-matrix calculations

A new algorithm to infer structural parameters such as refractive index and asphericity of cloud particles has been developed by use of in situ observations taken by a laser backscattersonde and an optical particle counter during balloon stratospheric flights. All three main particles, liquid, ice, and a no-ice solid (NAT, nitric acid trihydrate) of polar stratospheric clouds, were observed during two winter flights performed from Kiruna, Sweden. The technique is based on use of the T-matrix code developed for aspherical particles to calculate the backscattering coefficient and particle depolarizing properties on the basis of size distribution and concentration measurements. The results of the calculations are compared with observations to estimated refractive indices and particle asphericity. The method has also been used in cases when the liquid and solid phases coexist with comparable influence on the optical behavior of the cloud to estimate refractive indices. The main results prove that the index of refraction for NAT particles is in the range of 1.37-1.45 at 532 nm. Such particles would be slightly prolate spheroids. The calculated refractive indices for liquid and ice particles are 1.51-1.55 and 1.31-1.33, respectively. The results for solid particles confirm previous measurements taken in Antarctica during 1992 and obtained by a comparison of lidar and optical particle counter data.     

Optical properties and size distribution of aerosols derived from simultaneous measurements with lidar, a sunphotometer, and an aureolemeter

A new method is proposed to derive the optical properties and size distribution of aerosol in an air column from simultaneous measurements of the backscattering coefficient, the optical thickness, and the solar aureole intensity with lidar, a sunphotometer, and an aureolemeter. Inasmuch as the backscattering properties and the optical thickness depend on both the complex refractive index and the size distribution, whereas the forward-scattering properties depend mainly on the size distribution, real and imaginary indices of refraction and size distributions of aerosol are retrieved from these measurements. The real and the imaginary parts of the complex refractive index of an aerosol at a wavelength of 500 nm during the period from November 1991 to March 1992 obtained in Tsukuba, Japan, were estimated to be 1.46-1.48 and 0.005-0.014, respectively. It is inferred from the size distribution and an optical thickness fraction of stratospheric aerosols in the total columnar aerosols that these results reflect the influences of stratospheric aerosols that originated from the Mt. Pinatubo eruption.     

Measurement of the lidar ratio for atmospheric aerosols with a 180 degrees backscatter nephelometer

Laser radar (lidar) can be used to estimate atmospheric extinction coefficients that are due to aerosols if the ratio between optical extinction and 180 degrees backscatter (the lidar ratio) at the laser wavelength is known or if Raman or high spectral resolution data are available. Most lidar instruments, however, do not have Raman or high spectral resolution capability, which makes knowledge of the lidar ratio essential. We have modified an integrating nephelometer, which measures the scattering component of light extinction, by addition of a backward-pointing laser light source such that the detected light corresponds to integrated scattering over 176-178 degrees at a common lidar wavelength of 532 nm. Mie calculations indicate that the detected quantity is an excellent proxy for 180 degrees backscatter. When combined with existing techniques for measuring total scattering and absorption by particles, the new device permits a direct determination of the lidar ratio. A four-point calibration, run by filling the enclosed sample volume with particle-free gases of a known scattering coefficient, indicates a linear response and calibration reproducibility to within 4%. The instrument has a detection limit of 1.5 x 10(-7) m(-1) sr(-1) (~10% of Rayleigh scattering by air at STP) for a 5-min average and is suitable for ground and mobile/airborne surveys. Initial field measurements yielded a lidar ratio of ~20 for marine aerosols and ~60-70 for continental aerosols, with an uncertainty of ~20%.