大气气溶胶的垂直非均一对向上亮度和卫星遥感地表反射率的效应

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。     

A three-dimensional satellite retrieval method for atmospheric temperature and moisture profiles

A three-dimensional variational method is proposed to simultaneously retrieve the 3-D atmospheric temperature and moisture profiles from satellite radiance measurements. To include both vertical structure and the horizontal patterns of the atmospheric temperature and moisture, an EOF technique is used to decompose the temperature and moisture field in a 3-D space. A number of numerical simulations are conducted and they demonstrate that the 3-D method is less sensitive to the observation errors compared to the 1-D method. When the observation error is more than 2.0 K, to get the best results, the truncation number for the EOF＇s expansion have to be restricted to 2 in the 1-D method, while it can be set as large as 40 in a 3-D method. This results in the truncation error being reduced and the retrieval accuracy being improved in the 3-D method. Compared to the 1-D method, the rms errors of the 3-D method are reduced by 48% and 36% for the temperature and moisture retrievals, respectively. Using the real satellite measured brightness temperatures at 0557 UTC 31 July 2002, the temperature and moisture profiles are retrieved over a region （20°-45°N, 100°- 125°E） and compared with 37 collocated radiosonde observations. The results show that the retrieval accuracy with a 3-D method is significantly higher than those with the 1-D method.     

两种红外晴空辐射订正方法及其反演大气参数的比较

比较了目前开发的两种红外晴空辐射订正算法：1）匹配的红外和微波探测值融合的算法,如AIRS／AMSU晴空订正算法（大气红外探测器AIRS,先进的微波探测器AMSU）;2）匹配的红外成像与探测值融合的算法,如AIRS／MODIS晴空订正算法（中分辨率光谱成像仪MODIS）。结果表明,相对于MODIS的晴空观测值而言,AIRS／MODIS晴空订正算法优于AIRS／AMSU晴空订正算法,而且AIRS／MODIS晴空订正辐射值反演的大气温湿廓线与欧洲中期天气预报中心（ECMWF）的客观分析场更接近;尽管这两种晴空订正算法本质上相当不同,但都是有效且互补的,当微波探测资料不能获得时,融合红外成像仪和探测器资料就成为唯一可靠的、间接使用有云影响的红外观测值的办法。     

An algorithm for determination of aerosol opticalthickness from AVHRR imagery over oceans

Summary The uncertainty in aerosol size distributions is a main source of errors in aerosol optical thickness determined from satellite measurements. To reduce the errors resulting from the uncertainty in aerosol size distributions, we have performed sensitivity analyses. It is found the errors resulting from the uncertainty in aerosol size distribution can be considerably reduced by using the Junge power law to approximate the aerosol size distribution in an actual atmosphere, if the exponent value is determined at the same time. An iterative algorithm is then developed for the simultaneous determination of aerosol optical thickness and the exponent of the Junge power law over ocean areas from the upwelling radiances measured in AVHRR visible and near infrared channels. A number of numerical experiments are carried out to investigate the validity of the Junge power law approximation by assuming the aerosol size distributions in an actual atmosphere are bimodal with different mode parameters, and by using the actual aerosol size distributions determined at several places by Kaufman et al. (1994). The results show that the errors in determined aerosol optical thickness resulting from the Junge power law approach are significantly reduced. The iterative algorithm is investigated further by comparing the aerosol optical thickness deduced from satellite measurement with that observed by a sun photometer. Received October 10, 2001 Revised December 28, 2001     

用云和辐射传输模式研究对流性降水云微物理及辐射特性

利用中国气象科学研究院的三维对流云模式模拟了 1 998年发生在我国武汉地区的特大暴雨过程中的对流云。在模拟云的成熟阶段 ,模拟结果和地面最大降水量实况及热带测雨卫星TRMM (TropicalRainfallMeasureMission)的降水雷达PR(Pre cipitationRadar)的零度层高度和降水粒子达到的高度较接近。将该云物理模式的输出结果输入到Liu的三维辐射模式的输入场 ,模拟了以TRMM的微波成像仪TMI(TRMMMicrowaveImager)的扫描角为入射角 ,频率为 85 5GHz和 37 0GHz的星载微波辐射仪接受到的亮温 ,模拟的结果表明云中各微物理量的分布对上行微波辐射的影响较大。     

用于空间对地遥感的一个参数化辐射传输计算模式

一个足够精度的参数化向上亮度模式对空间对地遥感的大气订正应用是很有意义的。依据向上天空亮度对大气散射相函数、光学厚度、太阳天顶角、空间方位和天顶角等有关参数的依赖特性,基于大量的天空亮度数值模拟计算资料,本文发展了一个关于向上天空亮度的参数化模式。39440组的数值模拟对比资料表明,在气溶胶光学厚度#Aτt≤1,太阳天顶角小于72°,μ≤0.432 （天顶角小于65°）以及无云的条件下,由现在的参数化的模式所计算的向上亮度的误差一般小于6%。地表反射率越大,参数化模式的精度越高。参数化模式的精度一般随着光学厚度和太阳天顶角的增大而变差。     

Preliminary Retrieval of Aerosol Optical Depth from All-sky Images

The relationship between the radiance ratio (radiance at wavelength 450 nm to 650 nm) and aerosol optical depth (AOD) is analyzed in this paper by numerical simulation and a "LUT" (look-up table) approach is then presented for the retrieval of AOD from the radiance ratio. In this LUT approach, the AOD retrieval error depends mainly on the assumption of aerosol types. From the preliminary simulation, a typical error of 15%–20% in AOD obtained from the radiance ratio is estimated, due to neglecting changes in...     

A method for spaceborne synthetic remote sensing of atmospheric aerosol optical depth and vegetation reflectance

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风云三号卫星微波湿度计的扫描角偏差订正

首先统计分析了FY-3A卫星MWHS(Micro Wave Humidity Sounder,微波湿度计)2010年1月整月和8月28日—9月6日Level-1b全球观测亮度温度T_O和背景场(NCEP GFS 6 h预报场)用辐射传输模式(美国通用辐射传输模式CRTM 2.0版本)模拟的亮度温度T_B随扫描角的分布特征,发现通道3和4的观测随仪器扫描角有抖动、不连续现象。同时沿着仪器扫描线在星下点两测存在观测不对称现象,而且权重函数峰值越接近地面的通道该不对称现象越明显。在统计观测增量T_O-T_B随扫描角和纬度变化的基础上,定量给出了不同纬度带内(每隔5个纬度)MWHS通道3、4和5的扫描角偏差订正系数,该系数可直接提供给各种资料同化系统同化FY-3A MWHS资料时使用。     

The equilibrium constant of NO2 with N2O4 and the temperature dependence of the visible spectrum of NO2: A critical review and the implications for measurements of NO2 in the polar stratosphere

Measurements of stratospheric NO₂ by ground-based visible spectrometers rely on laboratory measurements of absorption cross-sections. We review low-temperature laboratory measurements, which disagree by amounts claimed to be significant. Our recalculation of their errors shows that in general disagreements are not significant and that errors in the ratios of cross-sections at low to room temperature are between ±3% and ±8.8%. Of these errors, up to ±3.5% was contributed by errors in the equilibrium constant,K _p, in those measurements where the pressure was above 0.1 mbar.We review measurements and calculations ofK _p, which were accurate to ±5% from 300 to 233 K. Each method was potentially flawed. For example, infrared measurements of the partial pressure of NO₂ ignored the dependence of absorption on total pressure. From thermodynamic theory, formulae forK _pcan be derived from expressions for the variation of heat capacity with temperature. Contrary to common belief, coefficients in the formulae used by spectroscopists were not derived from the thermodynamic quantities. Rather, they were fitted to measurements or to calculations. Hence, they are empirical and it is dangerous to extrapolate below 233 K, the lowest temperature of the measurements.There are no measurements of NO₂ cross-sections below 230 K. Extrapolation of these cross-sections to analysis of measurements of NO₂ at the low temperatures of the Arctic and Antarctic stratosphere is also dangerous. For satisfactory analysis of polar spectra, the NO₂ cross-sections should be measured at temperatures down to 190 K with a relative accuracy of ±1%. This difficult experiment would need a cell of minimum length 32 m whose length can be adjusted. Because their effects are circular, many errors cannot be removed simply. Although circular errors also arise in the measurements ofK _pand of the infrared spectrum, their weights differ from those in the visible spectrum. The optimum experiment might therefore simultaneously measure the visible and infrared spectra andK _p.     

Use of total precipitable water classification of a priori error and quality control in atmospheric temperature and water vapor sounding retrieval

This study investigates the use of dynamic a priori error information according to atmospheric moistness and the use of quality controls in temperature and water vapor profile retrievals from hyperspectral infrared (IR) sounders. Temperature and water vapor profiles are retrieved from Atmospheric InfraRed Sounder (AIRS) radiance measurements by applying a physical iterative method using regression retrieval as the first guess. Based on the dependency of first-guess errors on the degree of atmospheric moistness, the a priori first-guess errors classified by total precipitable water (TPW) are applied in the AIRS physical retrieval procedure. Compared to the retrieval results from a fixed a priori error, boundary layer moisture retrievals appear to be improved via TPW classification of a priori first-guess errors. Six quality control (QC) tests, which check non-converged or bad retrievals, large residuals, high terrain and desert areas, and large temperature and moisture deviations from the first guess regression retrieval, are also applied in the AIRS physical retrievals. Significantly large errors are found for the retrievals rejected by these six QCs, and the retrieval errors are substantially reduced via QC over land, which suggest the usefulness and high impact of the QCs, especially over land. In conclusion, the use of dynamic a priori error information according to atmospheric moistness, and the use of appropriate QCs dealing with the geographical information and the deviation from the first-guess as well as the conventional inverse performance are suggested to improve temperature and moisture retrievals and their applications.     

对流性降水云辐射特性研究

结合MM5模式和三维微波辐射传输模式,对2002年7月22～23日发生在湖北宜昌附近一次中尺度强降水过程中的强降水中心的对流性降水云的微波辐射特性进行了模拟,模拟结果表明：MM5模式可以较好地模拟此次降水过程;云中各微物理量的含量和分布对上行微波辐射亮温有重要影响;就物理方法而言,选用适当的云廓线,是利用微波信息反演降水的关键。     

GRAPES全球三维变分同化中卫星微波温度计亮温的背景误差及在质量控制中的应用

模式变量背景误差在观测空间的投影,也即观测变量的背景误差包含了变分同化系统的重要信息,其在诊断和分析变分同化系统中资料的影响等方面具有重要作用,特别是在背景场检查质量控制中。在GRAPES全球三维变分同化(3DVar)系统中仅给定了控制变量的背景误差,并未直接给定观测变量的背景误差。为了能够对GRAPES全球3DVar进行全面的诊断和分析,改进卫星微波温度计资料的质量控制,推导出GRAPES全球3DVar同化系统控制变量随机扰动方法估计观测变量的背景误差的公式,为分析和改进GRAPES全球3DVar提供了一个有力工具,并进而估计了AMSU-A亮温的背景误差,分析了AMSU-A不同通道亮温的背景误差特征,将其应用于GRAPES全球3DVar的AMSU-A亮温的背景场检查质量控制中。结果表明,控制变量随机扰动方法估计的GRAPES全球3DVar同化系统AMSU-A亮温的背景误差正确合理。同化循环预报试验结果表明,亮温的背景误差在背景场检查中的应用显著提高了GRAPES全球3DVar同化的亮温资料的数量,显著提高了GRAPES南半球对流层中高层位势高度场的预报技巧。在GRAPES全球3DVar同化系统中推导和实现的控制变量扰动方法为诊断和分析GRAPES全球3DVar观测资料同化效果提供了有力工具。      

飑线型降水云微波辐射特性的数值研究

本文将三维云的微物理模式的输出作为三维辐射传输模式的输入，对降水云的微波上行辐射率同地球物理参数间的关系进行了初步研究。在侧边界条件不对称的情况下，如果不考虑实际存在的云间相互辐射作用而模拟降水云的上行辐射率时，模拟出的亮温在低频段将低估卫星上测到的亮温值；在高频段则依降水云上层含冰量的大小而异，即在降水云上层含冰量小的区域，将低估星上测到的亮温，且低估的幅度较低频通道的大，而在降水云上层含冰量大的区域，可能高估星上测到的亮温，但高估的幅度较小。     

Sensitivity of retrieved atmospheric profiles from infrared radiances to physical and statistical parameters of the data assimilation system

Abstract

The direct assimilation of satellite radiances is now operational in a few forecast centres, providing global temperature (T) and moisture (Q) information. The critical parameters which influence the quality of the resulting analysis are mainly the selection of channels, the respective errors of the background field and radiance observations, and the quality of the radiative transfer model. These various aspects are studied from sensitivity experiments based on 1‐D variational assimilations using the ensemble of 19 infrared channels (HIRS) of the NOAA‐14 satellite.

It is shown that significant improvements in the retrievals would be obtained if the radiance observation error (measurement plus radiative transfer), currently estimated to be about equal to that of the background (in radiance units), were decreased. This could in principle be achieved by improving the forward radiative transfer model (RTM). Two RTMs suitable for radiance assimilation are compared in terms of analyzed increments, Jacobians, brightness temperature and equivalent background error. Important differences are noted for all of these interrelated measures. The existence of air‐mass dependent biases of fast radiative transfer models of the order of 1.5 K is confirmed in several channels from additional comparison with a line‐by‐line model. The importance of correctly specifying surface emissivity and the effective angle for downward calculations is demonstrated.

The paper also evaluates, in some detail, the impact of uncertainties on the background error covariance matrix. The uncertainty on the skin temperature (TJ error affects mostly the retrieval of that parameter; it has a modest impact on the T and Q profiles in the low troposphere. The uncertainty on the Q‐Q elements has more impact than that on the T‐T elements. Off‐diagonal elements of the background error covariance matrix are very important as they impose smoothness and level‐to‐level consistency, especially for Q retrievals. Finally, T_s‐T correlations, often ignored, could result in significant improvements in the retrieval of temperature at low levels. Research issues are discussed in the conclusion.     

大气遥感辐射传输模式的一种有效的Jacobian算法

介绍并验证了一种快速、精确地计算Jacobian的解析方法(辐射传输方程的线性化,简称LR方法),将其结果与NAST-I真正的线性模式及数值方法(差分方法)的Jacobian值进行比较。结果表明,这种解析算法不仅快速、精确,而且独立于辐射传输方程,在有效Jacobian计算中只需要输入大气透过率,可适用于任何垂直探测器权重函数的计算。     

A Method for Retrieving Vertical Ozone Profiles from Limb Scattered Measurements

A two-step method is employed in this study to retrieve vertical ozone profiles using scattered measure- ments from the limb of the atmosphere. The combination of the Differential Optical Absorption Spectroscopy (DOAS) and the Multiplicative Algebraic Reconstruction Technique (MART) is proposed. First, the limb radiance, measured over a range of tangent heights, is processed using the DOAS technique to recover the effective column densities of atmospheric ozone. Second, these effective column densities along the lines of sight (LOSs) are inverted using the MART coupled with a forward model SCIATRAN (radiative transfer model for SCIAMACHY) to derive the ozone profiles. This method is applied to Optical Spectrograph and Infra Red Imager System (OSIRIS) radiance, using the wavelength windows 571-617 nm. Vertical ozone profiles between 10 and 48 km are derived with a vertical resolution of 1 km. The results illustrate a good agreement with the cloud-free coincident SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) ozone measurements, with deviations less than ± 10% ( ± 5% for altitudes from 17 to 47 km). Furthermore, sensitivities of retrieved ozone to aerosol, cloud parameters and NO 2 concentration are also investigated.     

Mass transfer from discrete water drops on leaves in a cereal canopy

The boundary-layer resistance, r _d , for water vapour transfer from single drops on a wheat leaf was derived from field measurements of the evaporation rate, drop temperature and air humidity. Parameters are estimated in an equation to calculate r _d from drop diameter and wind speed. The relationship between resistance and wind speed is compared with that from other sources, and possible systematic errors in temperature measurements are examined using a model of the drop energy balance.On secondment from Department of Agricultural Sciences, University of Bristol, IACR, Long Ashton Research Station, Long Ashton, Bristol BS18 9AF, U.K.     

Determination of boundary-layer parameters using wind profiler/RASS and sodar/RASS in the frame of the LITFASS project

Summary ?Progress in technology as well as signal processing has promoted Wind Profiler Radar (WPR) or sodar with RASS additions to become standard tools in profiling of the atmospheric boundary layer. Apart from these instruments’ basic abilities in profiling mean winds and temperature, this paper will give an emphasis on the profiling of ABL height as well as the turbulent fluxes of sensible heat and momentum both, with respect to methods as well as with respect to realization. The special focus will thereby be laid on the demands for vertical profiling, which were defined within the LITFASS-project of the German Meteorological Service. In the frame of this project, some special measuring campaigns have been performed where remote-sensing systems were used to assess their abilities in profiling ABL parameters. On the base of some case studies from these campaigns comparisons are shown, where results from sodar/RASS and WPR/RASS measurements are compared to measurements from airborne sensor systems and results from numerical models. Regarding turbulent heat fluxes, we found excellent agreement for remotely-sensed flux profiles from WPR/RASS with both, numerical models and airborne in-situ measurements. However, as the inherent errors of the remotely-sensed fluxes are in the order of ± 20 ⋯ 30 W/m² typically, current signal processing does not allow to interpret small-scale vertical structures in the profiles with respect to surface inhomogeneities yet. Received June 16, 2001; revised February 20, 2002; accepted May 30, 2002     

Application of ATOVS microwave radiance assimilation to rainfall prediction in Summer 2004

Experiments are performed in this paper to understand the influence of satellite radiance data on the initial field of a numerical prediction system and rainfall prediction. First, Advanced Microwave Sounder Unit A （AMSU-A） and Unit B （AMSU-B） radiance data are directly used by three-dimensional variational data assimilation to improve the background field of the numerical model. Then, the detailed effect of the radiance data on the background field is analyzed. Secondly, the background field, which is formed by application of Advanced Television and Infrared Observation Satellite Operational Vertical Sounder （ATOVS） microwave radiance assimilation, is employed to simulate some heavy rainfall cases. The experiment results show that the assimilation of AMSU-A （B） microwave radiance data has a certain impact on the geopotential height, temperature, relative humidity and flow fields. And the impacts on the background field are mostly similar in the different months in summer. The heavy rainfall experiments reveal that the application of AMSU-A （B） microwave radiance data can improve the rainfall prediction significantly. In particular, the AMSU-A radiance data can significantly enhance the prediction of rainfall above 10 mm within 48 h, and the AMSU-B radiance data can improve the prediction of rainfall above 50 mm within 24 h. The present study confirms that the direct assimilation of satellite radiance data is an effective way to improve the prediction of heavy rainfall in the summer in China.