地球同步卫星资料的一种云地分离综合处理技术

利用多通道地球同步卫星资料,采用多通道阈值、基于晴空合成底图和云图时间序列的阈值和相似检测、有限区域动态阈值检测等方法,运用分步决策思路,对(60°S～60°N、45～165°E)区域内卫星云图分中高云和低云进行云地分离综合处理。经人工判断与自动云地分离结果对比分析表明,准确率达到90%以上。分析表明,考虑云和地(海)表在不同通道的亮温差异和随时间演变特点,建立并运用多种云地分离方法,有利于云地分离信息量的增加;提出的考虑云系分布时变特性的相似检测法,以及从有云和无云两个角度优先选择高可信度方法逐步检测,有利于云地分离准确率的提高。     

Catalysed self-cleaning of air on the earth's surface

Generally, it is assumed that UV-light, high temperature or reactive molecules like O₃ and OH are needed to activate gas reactions in air. In consequence, the catalytic activity on natural materials such as sand and soil on the earth's surface is assumed to be insignificant. We have measured O₂-dissociation rates on natural quartz sand at 40˚C and compared these with O₂-dissociation rates near 500˚C on materials with well-known catalytic activity. In terms of probabilities for dissociation of impinging O₂-molecules the measured rates are in the 10⁻¹²–10⁻⁴ range. We have also measured dissociation rates of H₂ and N₂, water-formation from H₂ and O₂ mixtures, exchange of N between N₂, NO _x and a breakdown of HNO₃, NO₂ and CH₄ on natural quartz sand at 40˚C. The measured rates together with an effective global land area have been used to estimate the impact of thermodynamically driven reactions on the earth's surface on the global atmospheric budgets of H₂, NO₂ and CH₄. The experimental data on natural quartz sand together with data from equilibrium calculations of air suggest that an expected increase in anthropogenic supply of air pollutants, such as NO _x or other “reactive” nitrogen compounds, hydrogen and methane, will be counter-acted by catalysis on the earth's surface. On the other hand, at Polar Regions and boreal forests where the “reactive” nitrogen concentration is below equilibrium, the same catalytic effect activates formation of bio-available nitrogen compounds from N₂, O₂ and H₂O.     

Triggering of atmospheric circulations by moisture inhomogeneities of the earth's surface

A two-dimensional mesoscale soil-atmosphere model is used to simulate the triggering of atmospheric convection by horizontally varying soil water content. The variation is periodic with a wavelength between 4 and 40 km, which is considered a realistic scale for the variation of land surface characteristics. Three stages of convection can be clearly discerned: a short initial stage when convection sets in and where the size of the conective cells is determined by , a mature stage with well developed cells whose size is still determined by , and a decay/transformation stage, characterized by the formation of narrow regions of strong updrafts and wide regions of moderate downdrafts, independent of . Parameters relevant for the transition are given, and the importance of the feedback between soil and atmosphere is demonstrated. The dependence of convective parameters, e.g., height of the convective layer, vertical velocity and fluxes of heat and moisture on is investigated. The calculations of the mature stage are compared with the predictions of a linear model.     

A validation of the multivariate and minimum residual method for cloud retrieval using radiance from multiple satellites

The Multivariate and Minimum Residual(MMR) cloud detection and retrieval algorithm, previously developed and tested on simulated observations and Advanced Infrared Sounder radiance, was explored and validated using various radiances from multiple sensors. For validation, the cloud retrievals were compared to independent cloud products from Cloud Sat, MODIS(Moderate Resolution Imaging Spectroradiometer), and GOES(Geostationary Operational Environmental Satellites). We found good spatial agreement within a single instrument, although the cloud fraction on each pixel was estimated independently. The retrieved cloud properties showed good agreement using radiances from multiple satellites, especially for the vertically integrated cloud mask. The accuracy of the MMR scheme in detecting mid-level clouds was found to be higher than for higher and lower clouds. The accuracy in retrieving cloud top pressures and cloud profiles increased with more channels from observations. For observations with fewer channels, the MMR solution was an "overly smoothed" estimation of the true vertical profile, starting from a uniform clear guess. Additionally, the retrieval algorithm showed some meaningful skill in simulating the cloudy radiance as a linear observation operator, discriminating between numerical weather prediction(NWP) error and cloud effects. The retrieval scheme was also found to be robust when different radiative transfer models were used. The potential application of the MMR algorithm in NWP with multiple radiances is also discussed.     

利用全天空可见光图像反演天空辐亮度

由中国科学院大气物理研究所LAGEO实验室研制和开发的地基全天空成像仪,可实现地基全天空自动化观测,文中首先对全天空成像仪仪器及性能进行介绍.辐亮度是气象科学研究中基础而重要的气象要素,而全天空成像仪记录的是可见光红、绿、蓝三波段辐射信息的灰度值图像,因而无法直接应用到气象研究中.为能够从灰度值图像中获取天空辐亮度信息,文中详细介绍了与亮度反演密切相关的几个重要标定实验,包括儿何标定、光学标定,以标定参数为基础并结合全天空仪器成像原理提出了一个由可见光灰度图像反演相对天空辐亮度分布的算式算法.文中还利用大气物理研究所香河观测站(39.75°N,116.96°E)同时观测的全天空成像仪以及CIMEL光度计所观测的天空辐亮度数据(440 nm波长),对该反演算式进行检验和比对,结果表明,所提出的算法进行天空辐亮度分布反演可行,该算法将灰度图像与天空辐亮度建立了联系,有利于观测图像数据与数值模式模拟工作的相互对比和验证,有利于观测图像数据在模式研究中的应用.     

SIMULTANEOUS DETERMINATION OF AEROSOL SIZE DISTRIBUTION AND REFRACTIVE INDEX AND SURFACE ALBEDO FROM RADIANCE—PART II: APPLICATION

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.     

SIMULTANEOUS DETERMINATION OF AEROSOL SIZE DISTRIBUTION AND REFRACTIVE INDEX AND SURFACE ALBEDO FROM RADIANCE－PART I: THEORY

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.     

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。     

基于偏差原则利用MODIS红外资料反演大气廓线以及表层温度

遥感方程或大气辐射传输方程是属于第一类非线性Fredholm积分方程,这类方程的显著特征是不适定的,尤其此类问题解的不稳定性,增加了反演的难度.因此需要研究控制反演不稳定性和提高反演精度的有效方法.为了使解稳定,光滑参数γ作为约束因子是必要的.文中结合牛顿非线性迭代法反演大气廓线,利用偏差原则来最优选择光滑参数γ,即在同步反演大气廓线的同时对γ采用分步迭代的原则.最后利用中分辨率和成像光谱仪(MODIS)红外资料进行反演试验,反演结果表明采用偏差原则选取γ明显优于经验法,反演的表层温度和大气可降水量与美国国家宇航局(NASA)的MOD07产品类似.     

Ensemble reconstruction of the atmospheric column from surface pressure using analogues

We present a statistical method to reconstruct continuous atmospheric fields on various pressure levels, given a constraint at the surface. The method is based on analogues of circulation and taking into consideration the time sequence of the analogues. The method is tested on the 2001–2011 period, with an emphasis on the year 2010. We base the atmospheric reconstruction on reanalysis data from 1948 to 2000, and use a constraint of sea-level pressure for 2001–2011. The pattern correlation scores appear to be significant most of the time, although score flaws are occasionally detected. Those flaws are mainly due to the time continuity constraint that is imposed on the reconstruction, which lowers the possibility of finding matching analogues. This method offers an ensemble of atmospheric reconstructions, and presents a computationally cheap alternative to data assimilation for a climate model, although with lower scores.     

Precipitable water evaluations from infrared sun‐photometric measurements analyzed using the atmospheric hygrometry technique

Measurements of direct solar irradiance were taken employing 4 different sun‐photometers at near infrared wavelengths, suitable for use in atmospheric hygrometry. This technique utilising a set of spectral ratios, in and out of selected water vapour absorption bands, was applied to the measurements to obtain accurate evaluations of precipitable water. For all the hygrometric ratios given by the 4 sun‐photometers used at the 3 stations of Sagres, Monchique and Mt. Foia, during the CLEARCOLUMN experiment, we determined the calibration curves by correcting them for the Rayleigh scattering effects and, then, plotting the natural logarithms of such corrected ratios versus the square root of the water vapour mass present along the atmospheric slant path. The regression lines drawn for the various scatter diagrams were estimated to give evaluations of precipitable water with an uncertainty of less than 5%, 3% and 10% at the 3 stations, respectively. The calibration curves of the sun‐photometer located at the Sagres station were determined using the precipitable water evaluations obtained from the local radiosounding measurements taken on 5 clear‐sky days. Those of the sun‐photometers used at the Monchique and Mt. Foia stations were instead determined through intercomparison between subsets of measurements simultaneously taken with various instruments at Sagres and Mt. Foia. Using these calibration curves, we examined all the field measurements determining the time‐patterns of precipitable water at the 3 stations. During the period from 16 June to 25 July 1997, precipitable water was found to vary between 1.1 and 3.7 g cm⁻² at the Sagres station (with an accuracy within ±13%), between 1.0 and 2.8 g cm⁻² at Monchique (±11%) and between 0.8 and 3.0 g cm⁻² at the top of Mt. Foia (±26%).     

热带海表风速与海表温度日变化关系分析

星载可见光/红外仪器因其波长缺乏穿透云的能力,只能观测到云顶及其下部有限深度的信息,而星载被动微波仪器则因其波长较长,具有穿透云的能力而能获得云体信息,因此星载被动微波仪器较可见光/红外仪器观测云和降水更具有优势。自20世纪70年代末至今,美国投入了大量星载被动微波仪器,服务于天气预报等领域,促进了云和降水等参数的被动微波遥感反演算法的快速发展。本文聚焦星载被动微波遥感反演洋面云液态水研究的进展,旨在提升我国的星载被动微波仪器遥感应用能力。文章首先简介了几种微波辐射传输模式形式,其次介绍了被动微波通道（频率）对洋面参数和云液态水的敏感性研究,然后介绍了被动微波反演洋面云液态水的统计反演算法、物理反演算法、物理与统计相结合的反演算法、被动微波多通道多参数的同步反演算法、被动微波与可见光/红外相结合的反演算法,最后探讨了未来该领域研究的发展方向。

     

Atmospheric correction of infrared measurements of sea surface temperature using channels at 3.7, 11 and 12 Μm

Atmospheric effects upon the radiometric determination of surface temperature were studied for channels centered at 3.7, 11 and 12 m. The error due to the atmosphere is least for the channel centered at 3.7 m, which is a real advantage. The use of a linear combination of two or all three of these channels allows one to eliminate most of the atmospheric effect. If instrumental noise of from 0.1 to 0.2 K is accounted for in each channel, the best results are obtained by a combination of the two channels at 3.7 and 12 m.     

Cloud climate investigations in the Nordic region using NOAA AVHRR data

Summary A method to estimate monthly cloud conditions (monthly cloud frequencies) from multispectral satellite imagery is described. The operational cloud classification scheme SCANDIA (the SMHI Cloud ANalysis model using DIgital AVHRR data), based on high resolution imagery from the polar orbiting NOAA-satellites, has been used to produce monthly cloud frequencies for the entire year of 1993 and some additional months in 1991, 1992, 1994 and 1995. Cloud analyses were made for an area covering the Nordic countries with a horizontal resolution of four km. Examples of seasonal, monthly and diurnal variation in cloud conditions are given and an annual mean for 1993 is presented.Comparisons with existing surface observations showed very good agreement for horizontal cloud distributions but approximately 5% smaller cloud amounts were found in the satellite estimations. The most evident problems were encountered in the winter season due to difficulties in identifying low-level cloudiness at very low sun elevations. The underestimation in the summer season was partly fictious and caused by the overestimation of convective cloud cover by surface observers.SCANDIA results were compared to ISCCP (International Satellite Cloud Climatology Project) cloud climatologies for two selected months in 1991 and 1992. ISCCP cloudiness was indicated to be higher, especially during the month with anticyclonic conditions where a cloudiness excess of more than 10% were found. The regional variation of cloud conditions in the area was found to be inadequately described by ISCCP cloud climatologies. An improvement of the horizontal resolution of ISCCP data seems necessary to enable use for regional applications.The SCANDIA model is proposed as a valuable tool for local and regional monitoring of the cloud climatology at high latitudes. More extensive comparisons with ISCCP cloud climatologies are suggested as well as comparisons with modelled cloudiness from atmospheric general circulation models and climate models. Special studies of cloud conditions in the Polar areas are also proposed.With 14 Figures     

Interrelationships between atmospheric turbidity,the diffusely reflected visible radiation at the top of the earth's atmosphere and the global solar radiation at the surface

Summary The flux of radiation emerging at the top and bottom of a realistic model of a cloud-free, plane-parallel, vertically inhomogeneous turbid atmosphere has been computed for different values of atmospheric turbidity and surface albedo in 83 unequal spectral intervals over the short-wave or solar radiation (0.285–2.5 m) regime. These computations have been utilized to determine the diffusely reflected radiation at the top of the atmosphere in the spectral interval 0.535–0.7035 m (which covers the visible channels of the radiometers onboard the Geosynchronous Operational Environmental Satellites and the NOAA polar orbiting satellites) and in the spectral interval 0.375–0.7035 m. The total global solar radiation (0.285–2.5 m) reaching the surface has also been determined. Simple linear regression relationships have been established between (i) the reflected radiation at the top and atmospheric turbidity and (ii) between the global radiation at the surface and the reflected radiation at the top. These regression relationships yield coefficients of determination very close to unity. The implications of this strong linear dependence of the reflected radiation on atmospheric turbidity and of the global radiation at the surface on the reflected radiation at the top to satellite-based studies of the feasibility of estimation of the insolation (global radiation) at the surface are briefly mentioned.With 3 Figures     

气象卫星遥感地表温度推算近地表气温方法研究

气温是各种植物生理、水文、气象、环境等模式或模型中的一个非常重要的近地表气象参数.多年来气温数据以离散的常规气象站点观测为主,连续分布的格点气温数据则以站点资料插值而得到,分辨率低,无法反映地形等下垫面因素对局地气温的影响,在农业气候区划等研究中具有一定的局限性.随着卫星遥感地表温度算法的日趋成熟,为探讨卫星遥感地表温度数据在气温观测中的可能性和可行性,利用全中国2340个站点1998 2007年的逐旬平均最高气温数据,以及相应时段的NOAA/AVHRR旬最高地表温度数据,以线性回归及拟合模型为主,通过考虑植被指数、土地覆盖类型、季节、风速、气压、降水等各类影响因子,建立了旬最高地表温度与旬平均最高气温间的推算模型,并利用未参与建模的2002-2003年的常规气象站点气温数据,同时与推算气温和插值气温结果进行对比分析.结果表明,利用卫星遥感地表温度数据推算的旬值气温数据可取得较高的精度,尤其在地形复杂地区以及站点稀疏地区精度明显高于插值气温结果.     

地形积层混合云模式数值试验研究

本文采用数值试验对比分析的方法,利用一维半地形积层混合云模式,分别进行引入与不引入极端水汽源的模拟试验。研究表明,一旦引入极端水汽源,地形积层混合云系统即成为一个极为有效的造雨系统。极端水汽源的引入提供了更加饱和的环境,维持更久的辐合场,还增大了冰相粒子对云水的碰并。这些初步认为是暴雨产生的主要物理原因。