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1.
Based on the radiative transfer calculation results, three approximate expressions of the sky radiance in almucantar and its increment caused by surface albedo are presented. They are simple, but accurate enough. The dependence of the fitted aerosol scattering phase functions on refractive index is also studied, and its reasonable form is given. For Junge size distribution, the approximate equations of the phase functions with some special scattering angles are obtained. These approximate equations significantly simplify the retrieval algorithm of simultaneous determination of aerosol size distribution and its refractive index and surface albedo. This method can be realized with a microcomputer, and has been used to process and analyse the experimental data measured in Hefei of Anhui Province.  相似文献   

2.
Analyzing in detail the dependence of sky radiance on aerosol optical property and surface albedo, we present a new method for simultaneous determination of aerosol size distribution, its wavelength-dependent refractive index and surface albedo. The aerosol scattering phase function near 10o, its weighted phase function near 40o introduced in this paper, which can be inferred from sky radiance data, and the radiance near 90o are respectively used in retrieving the real part of refractive index, its imaginary part and surface albedo. Results in numerical experiments are satisfactory under different given conditions.  相似文献   

3.
Aerosol optical parameters, polarized phase function and single-scattering albdeo, have been retrieved from ground-based sun photometer measurements in Beijing 2003. The measured aerosol optical thickness varies from 0.12 to 0.77 with an average value of 0.39. The measured Ångström coefficient ranges from 0.75 to 1.47 with an average value of 1.21. The retrieved single-scattering albedo at 870 nm is within the 0.76–0.94 range and the average value is 0.85, suggests there are considerable aerosol absorptions in Beijing. The maximum value of retrieved polarized phase function at 870 nm ranges from 0.068 to 0.225 with an average value of 0.16, and it illustrates good correlations with the Ångström coefficient, i.e. the relative size of aerosol particles. Analyses of measurements and theoretical calculations show the polarized phase function is sensitive to aerosol size distribution and complex refractive index, especially the imaginary part of the refractive index which denotes aerosol light absorbing effects. These results suggest that the polarized phase function is an effective and unique aerosol optical parameter and is able to improve the retrieval of aerosol physical properties.  相似文献   

4.
This paper presents and analyzes experimental results in simultaneous determination of atmospheric colum-nar aerosol size distribution, refractive index and surface albedo by use of the radiance data in almucantar measured by a radiometer. 32 groups of data measured in Beijing during winter show that the imaginary part of refractive index for 0.6943 μm wavelength ranges from 0.022 to 0.079 with a mean of 0.0527. The mean real part and surface albedo are 1.537 and 0.287, respectively. The imaginary part was found to be less in autumn than that in winter, especially after raining. For 0.399 μm and 0.6943 μm wavelengths, the mean sur-face albedos are 0.101 and 0.222, and the mean imaginary parts are 0.0241 and 0.0129, respectively.  相似文献   

5.
The air quality modeling system RAMS （Regional Atmospheric Modeling System）-CMAQ （Models-3 Community Multi-scale Air Quality） is developed to simulate the aerosol optical depth （AOD） and aerosol direct forcing （DF）. The aerosol-specific extinction, single scattering albedo, and asymmetry factor are parameterized based on Mie theory taking into account the aerosol size distribution, composition, refractive index, and water uptake of solution particles. A two-stream solar radiative model considers all gaseous molecular absorption, Rayleigh scattering, and aerosols and clouds. RAMSCMAQ is applied to simulate all major aerosol concentrations （e.g., sulfate, nitrate, ammonium, organic carbon, black carbon, fine soil, and sea salt） and AOD and DF over East Asia in 2005. To evaluate its performance, the simulated AOD values were compared with ground-based in situ measurements. The comparison shows that RAMSCMAQ performed well in most of the model domain and generally captured the observed variations. High AOD values （0.2-1.0） mainly appear in the Sichuan Basin as well as in central and southeastern China. The geographic distribution of DF generally follows the AOD distribution patterns, and the DF at the top-of-the-atmosphere is less than -25 and -20 W m^-2 in clear-sky and all-sky over the Sichuan Basin. Both AOD and DF exhibit seasonal variations with lower values in July and higher ones in January. The DF could obviously be impacted by high cloud fractions.  相似文献   

6.
利用AERONET观测资料从气候学的角度比较分析了2001-2011年东亚地区沙尘天气发生时沙尘源区和下游区大气气溶胶光学特性。结果表明：沙尘期间沙尘源区气溶胶光学厚度明显大于下游区,而Angstr?m波长指数却小于下游区,当沙尘暴出现时会降至零甚至负值。气溶胶粒子尺度体积谱分布除敦煌为单峰外,其余各站均呈双峰分布,香河和北京的细粒子浓度明显大于西北地区,这可能是由细的沙尘粒子和污染气溶胶共同造成。在440-1020 nm范围内,中国地区气溶胶单次散射反照率平均值为0.93,韩国和日本站分别为0.93和0.94。沙尘源区与下游区相比,复折射指数实部偏大,虚部偏小。总体来说,沙尘天气下东亚地区在4个波段内平均不对称因子为0.70。  相似文献   

7.
均一模式和两层模式是两个忽略气溶胶垂直非均一、并广泛用于卫星遥感的辐射模式。通过两个模式的数值模拟，分析了气溶胶的垂直非均一对向上天空亮度和卫星遥感地面反射率的效应。数值模拟选用了２４个有代表性的气溶胶模式。对于具有强分子散射的卫星短波通道，由于分子和气溶胶散射性的明显不同，应用均一和两层模式计算的向上亮度往往存在较大误差。对长波通道，如果气溶胶的光学特性随高度变化不大，该亮度误差较小，但如果存在不同散射相函数和一次散射反照率的气溶胶层，该误差仍可能较大。对于干净的大气，由均一和两层模式计算的亮度误差可分别高达３１．４％和３１．５％，而对于混浊的大气，该误差可分别高达６７．８％和５９．２％。该亮度误差可以引起地表反射率解存在大的不确定性，特别是对于短波通道和强吸收的气溶胶。对于包含强吸收气溶胶的混浊大气，均一和两层模式不适合于大气订正应用。  相似文献   

8.
张敬斌  胡欢陵 《大气科学》1993,17(5):636-640
我们利用Junge谱对多道光电粒子计数器的测量谱进行了模拟,根据光散射的米氏理论,考察了气溶胶小粒子对其消光、后向散射及消光后向散射比的影响情况,对估计由实测谱及折射指数计算以上三个参量所带来的误差具有一定参考价值.  相似文献   

9.
An approximate expression of the sky radiance in almucantar is confirmed in this paper. Under the conditions with molecular optical depth<0.3, aerosol (or cloud) optical depth<0.6, solar zenith angle< 75° and scattering angle<30°, the errors of the sky radiance and the aerosol phase function computed from the expression are respectively less than 8 % and 10 %, but the phase functions computed from Box-Deepak formula and single-scattering formula can be 84 % and 260 % more than the exact value, respectively. Furthermore, by use of the expression we have inferred the volume scattering functions of 1°≤θ≤30° for retrieving aerosol size distribution with the conclusion that the distribution information in the range of 0.1相似文献   

10.
The albedo of snow for different cloudiness conditions is an important parameter in the Earth's radiation budget analysis and in the study of snowpack's thermal conditions. In this study an efficient approximate method is derived to calculate the incident spectral solar flux and snow-cover albedo in terms of different atmospheric, cloud, and snow parameters. The global flux under partially cloudy skies is expressed in terms of the clear sky flux and a coefficient which models the effect of scattering and absorption by cloud patches and multiple reflections between the cloud base and snowcover. The direct and the diffuse components of the clear sky flux are obtained using the spectral flux outside the atmosphere and the spectral transmission coefficients for absorption and scattering by molecules and aerosols.The spectral snow reflectance model considers both specular surface reflection and volumetric multiple scattering. The surface reflection is calculated by using a crystal-shape-dependent bidirectional reflectance distribution function; the volumetric multiple scattering is calculated by using a crystal-size-dependent approximate solution in the radiative transfer equation. The input parameters to the model are atmospheric precipitable water, ozone content, turbidity, cloud optical thickness, the size and shape of ice crystals of snow and surface pressure. The model yields spectral and integrated solar flux and snow reflectance as a function of solar elevation and fractional cloudcover.The model is illustrated using representative parameters for the Antarctic coastal regions. The albedo for a clear sky depends inversely on the solar elevation. At high elevations the albedo depends primarily upon the grain size; at low elevation the albedo depends on grain size and shape. The gradient of the albedo-elevation curve increases as the grains become larger and faceted. The albedo for a densely overcast sky is a few percent higher than the clear-sky albedo at high elevations. A simple relationship between grain size and the overcast albedo is obtained. For a set of grain size and shape, the albedo as a function of solar elevation and fractional cloud cover is tabulated.  相似文献   

11.
段民征  吕达仁 《大气科学》2007,31(5):757-765
陆地上空标量辐射对地表反射率和大气气溶胶散射都具有很强的敏感性,而偏振反射只对大气气溶胶敏感,对地表不敏感。根据这个原理并结合POLDER(POLarization and Directionality of Earth Reflectance)资料的特点,作者提出综合利用标量辐射和偏振反射信息来实现陆地上空大气气溶胶和地表反照率的同时反演。首先,利用多角度偏振辐射观测提取大气气溶胶光学参数,再利用标量辐射测量对偏振反演结果作进一步筛选和订正,同时获得地表反射率。数值模拟试验结果证明,仅利用偏振信息只能获取大气气溶胶信息,而且其结果误差较大,特别是对于散射作用较强的短波长通道如670 nm误差更大,但经过标量辐射订正后的结果得到明显改善,气溶胶光学厚度和地表反射率与真实值之间相关系数都达到0.99以上。为提高查找表的计算效率,提出并建立了反演方案所需要的半参数化数值表,利用内插方法寻求气溶胶光学厚度和地表反射率的数值解的反演方法。  相似文献   

12.
In this paper, the principle to determine the atmospheric columnar Mie optical depth from downward total solar radiative flux is theoretically studied, and the effect on Mie optical depth solution of the errors in surface albedo, single scattering albedo, asymmetrical factor of scattering phase function, instrumental constant and the approximate expression of diffusion flux is analyzed, and then a method for determining, surface albedo in shorter wavelength range is presented.  相似文献   

13.
With the data of complex refractive index of sulfate aerosol,the radiative properties of the aerosol under 8 relative humidity conditions are calculated in this paper.By using the concentration distribution from two CTM models and LASG GOALS/AGCM,the radiative forcing due to hygroscopic sulfate aerosol is simulated.The results show that:(1)With the increase of relative humidity,the mass extinction coefficiency factor decreases in the shortwave spectrum;single scattering albedo keeps unchanged except for a little increase in longwave spectrum,and asymmetry factor increases in whole spectrum.(2)Larger differences occur in radiative forcingsimulated by using two CTM data,and the global mean forcing is -0.268 and -0.816 W/m2,respectively.(3)When the impact of relative humidity on radiative property is taken into account,the distribution pattern of radiative forcing due to the wet particles is very similar to that of dry sulfate,but the forcing value decreases by 60%.  相似文献   

14.
In this paper the dependence of the ratio k (the atmospheric extinction-to-backscattering ratio) upon the aerosol refractive index and size distribution is theoretically studied in ruby lidar measurements. An empirical expression for the ratio k is then established. Moreover the effect of molecular scattering on the ratio k is discussed.  相似文献   

15.
《Atmospheric Research》2005,73(1-2):37-43
To account for surface reflection is a major and most complex issue of any satellite aerosol retrieval algorithm. The surface contribution to the satellite signal is usually calculated assuming Lambertian reflection. Then the problem is reduced to the calculation of total atmospheric transmittance and spherical albedo. Usually, these parameters are stored in so-called look-up tables (LUTs), which can be quite large. The main aim of this paper is the parameterization of these look-up tables in terms of simple approximate equations, which can be subsequently used in aerosol remote sensing techniques over reflecting land surfaces.  相似文献   

16.
Abstract

Ground‐based sunphotometry measurements acquired under clear sky conditions can be used to investigate atmospheric aerosol optical properties. Such measurements are not only important in their own right as a technique for monitoring generic aerosol dynamics, but also represent a direct means of evaluating the contribution of aerosol induced radiative forcing in the modelling of climate change. In this paper we analyze derived aerosol optical properties using datasets from the Canadian AEROCAN (AERosol CANada) sunphotometer network.

The AEROCAN network currently includes eight sunphotometers distributed across Canada at sites chosen in order to obtain a diverse sampling of continental, maritime and arctic aerosols. Some of these sites have been operational since 1993 as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS). These instruments permit standard and automatic multi‐wavelength measurements of solar extinction radiance centred on the solar disk as well as sky radiance scans off the solar disk. These data yields aerosol optical depth, the Ångström exponent, aerosol particle volume size distribution, refractive index, column‐averaged single scattering albedo, and precipitable water vapour content.

Spatial and temporal trends of these parameters as well as observed inter‐correlations are discussed. The results demonstrate the utility and significance of these types of measurements and illustrate the potential applications of networked sunphotometry data.  相似文献   

17.
Main optical characteristics of desert dust, such as phase function and single scattering albedo, have been derived from combinations of sun-/sky-radiometer and satellite measurements during the SAMUM experiment (10 May–10 June 2006) at the site Porte au Sahara (30.237°N, 5.607°W) in South Morocco. Scattering phase functions have been retrieved using combined data of spectral aerosol optical thickness (AOT) and spectral sky brightness in the almucantar, considering non-spherical light scattering. Intercomparisons of modelled top-of-atmosphere (TOA) reflectance with satellite observations of the Medium Resolution Imaging Spectrometer (MERIS) and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography () instrument have been used for the estimation of spectral single scattering albedo. For the radiative transfer calculations scattering phase functions and AOT from ground-based observations have been used. The spectral single scattering albedo ranges from 0.93 in the blue to 0.98 at 753 nm.  相似文献   

18.
利用地面激光雷达、太阳光度计观测反演气溶胶光学特性参数,结合PM2.5观测数据,分析了2018年1月25—28日北京一次完整污染过程中气溶胶光学特性变化。基于观测数据,利用短波辐射传输模式计算了不同程度污染日,晴空背景下气溶胶对辐射加热率的改变程度。结果表明:清洁日（25日）,PM2.5日平均质量浓度为19.00 μg·m-3,440 nm气溶胶光学厚度为0.13,单次散射反照率为0.87,整层气溶胶消光系数低于0.10 km-1,短波辐射均为增温效应;污染期间（26—27日）,PM2.5日平均质量浓度为83.21 μg·m-3,气溶胶光学厚度为2.48,气溶胶散射能力增强,单次散射反照率达到0.94,气溶胶主要消光层厚度提升至3.00 km高度,消光系数平均值为0.43 km-1,气溶胶在垂直方向的变化导致气溶胶中上层（1.50~3.00 km高度）加热作用强烈,短波辐射加热率平均值达到13.89 K·d-1,而低层（1.50 km高度以内）加热作用较弱,加热率平均值仅为0.99 K·d-1。气溶胶散射能力增强导致加热作用减弱,污染日加热率对于气溶胶散射能力变化更敏感。  相似文献   

19.
由于陆地地表反照率的复杂性,陆地上空气溶胶的反演一直是卫星对地观测的一个难点,针对这个难点,作者提出联合利用偏振反射率和总反射率提取陆地上空大气气溶胶光学厚度和地表反照率及其区域分布的反演方案,提出了利用NCEP资料订正由海拔高度引起的Rayleigh散射变化的具体方法,并利用POLDER（POLarization and Directionality of Earth's Reflectance）的LEVEL-1B资料进行实际反演计算,给出中国华北地区气溶胶光学厚度和地表反照率的区域分布。反演结果与地基观测进行了对比验证分析,结果表明,综合利用标量辐射和偏振信息的可以实现区域乃至全球尺度的大气气溶胶和地表反照率的定量反演。  相似文献   

20.
It is well established that aerosols affect the climate in a variety of ways. In order to understand these effects, we require an insight into the properties of aerosols. In this paper we present a study of aerosol properties such as aerosol optical depth (AOD), single scattering albedo (SSA) and aerosol radiative forcing (ARF) over mega city of Lahore (Pakistan). The data from Aerosol Robotic Network (AERONET) have been used for the period December 2009 to October 2011. The seasonal average values of AOD, asymmetry parameter (ASY) and volume size distribution in coarse mode were observed to be highest in summer. On the other hand, the average values of Angstrom exponent (AE) and imaginary part of refractive index (RI) were found to be maximum in winter. The average value of real part of RI was found to be higher in spring than in all other seasons. The SSA exhibited an increasing trend with wavelength in the range 440 nm–1020 nm in spring, summer and fall indicating the dominance of coarse particles (usually dust). However, a decreasing trend was found in winter in the range 675 nm–1020 nm pointing towards the dominance of biomass and urban/industrial aerosols. As far as aerosol radiative forcing (ARF) is concerned, we have found that during the spring season ARF was lowest at the surface of Earth and highest at top of the atmosphere (TOA). This indicates that the atmosphere was warmer in spring than in all the remaining seasons.  相似文献   

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