Remote sensing of cirrus optical and microphysical properties from ground-based infrared radiometric Measurements-part II: retrievals from CRYSTAL-FACE measurements

The ground-based infrared radiance measurements acquired on July 14, 20, and 28, 2002 during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers Florida Area Cirrus Experiment (CRYSTAL-FACE) campaign have been used for simultaneously retrieving the optical thickness and effective particle size on the basis of the retrieval algorithm reported in the preceding counterpart of this paper. The corresponding ice water path is derived from the retrieved optical thickness and effective particle size. Specifically, the data used for the retrieval include: 1) the infrared radiance spectrum observed by an atmospheric emitted radiance interferometer at the surface; 2) the sky condition and cloud height determined from a sky imager and a micropulse lidar; and 3) the sounding data for the profiles of temperature, pressure, and relative humidity. For these three case studies, the retrieved cirrus optical thickness, effective particle size, and ice water path are in the range of 0.2-1.5, 18-42 /spl mu/m, and 2-15 g /spl middot/ m/sup -2/, respectively. Furthermore, error analyses show that the retrieval uncertainties of the optical thickness and effective particle size are less than 15% if the uncertainty of water vapor vertical profile is within 5%. The retrieval errors are within 10% if the uncertainty of cloud temperature is within 7 K.     

Remote sensing of cirrus optical and microphysical properties from ground-based infrared radiometric Measurements-part I: a new retrieval method based on microwindow spectral signature

The surface radiance spectrum within the terrestrial infrared window (i.e., wavelengths between 8-12 /spl mu/m or wavenumbers between 833-1250 cm/sup -1/) is sensitive to the optical and microphysical properties of cirrus clouds. Numerous microwindows where atmospheric absorption is minimum exist in the spectral regions of 820-960 cm/sup -1/ and 1100-1240 cm/sup -1/. The minimum radiances at the microwindows in these two spectral regions can be fitted by using two linear lines. The slope of the fitting line for the spectral region of 820-960 cm/sup -1/ is sensitive to the effective size of ice crystals within cirrus clouds, whereas the intercept of the fitting line for the spectral region of 1100-1240 cm/sup -1/ is sensitive to the optical thickness of the clouds. Based on this spectral feature, a new retrieval method has been developed for simultaneously retrieving cirrus optical thickness and the effective particle size of ice crystals. Furthermore, the ice water path of cirrus clouds can be estimated from the retrieved values of cloud optical thickness and effective particle size.     

AMSR-E/2观测辐射值反演水成物参数

基于先进的微波扫描辐射计AMSR-E/2观测的辐射值,利用-维变分算法(1D-Var)反演各类水成物(云水、雨水和云冰)的垂直廓线,并对其反演结果进行检验。以2014年8月台风"夏浪"为例,分两步对变分反演的云微物理参数进行了检验。首先,将反演的各类水成物含量补充到辐射传输模式的输入场,观测算子模拟的AMSR-2各通道亮温与实况观测相比非常接近,可以很好地模拟出台风外形、强度及螺旋结构。其次,将反演的水成物廓线与载在Cloud Sat上的云雷达CPR同时段观测的雷达反射率因子进行对比,发现反演出的云水、雨水含量大值区与毫米波云雷达观测的雷达反射率因子高值区一一对应,进一步说明1D-Var反演的水成物参数精度很高。然而,由于星载AMSR-E/2观测通道少且空间分辨率低,对尺度较小、较薄的云不敏感,同时对云层较厚的密闭云区和多层云区反演能力也有限。     

Simulation of the Ku-band Radar altimeter sea ice effective scattering surface

A radiative transfer model is used to simulate the sea ice radar altimeter effective scattering surface variability as a function of snow depth and density. Under dry snow conditions without layering these are the primary snow parameters affecting the scattering surface variability. The model is initialized with in situ data collected during the May 2004 GreenIce ice camp in the Lincoln Sea (73/spl deg/W; 85/spl deg/N). Our results show that the snow cover is important for the effective scattering surface depth in sea ice and thus for the range measurement, ice freeboard, and ice thickness estimation.     

适用于遥感应用的辐射传输高精度快速计算方法

准确的散射辐射方向特征与辐射传输能量守恒的物理要求是一切算法的有效性准则。在有限计算资源的限制下,寻找最优的有限展开算法,获得能量守恒物理要求下的散射方向特征的准确性,是多年来辐射传输算法的追求目标。在以有限流数离散化辐射传输方程进行数值求解过程中,要保证数值计算中的积分守恒,流数有限要求粒子散射相函数必须截断,而不合适的截断容易导致解的误差,尤其是当大气中存在强前向散射的大粒子时（如云滴、沙尘暴事件过后的沙尘）,截断的相函数会出现振荡,从而导致解的虚假振荡特性。散射相函数无限扩展可以消除这种虚假振荡,但容易导致数值积分能量不守恒和解的不稳定。本文从原理上对这种虚假振荡和不稳定现象进行了分析,并给出两种用较少流数达到较高的计算精度的高效计算方法,这些算法对于遥感方法研究、GCM气候模式中辐射强迫的参数化研究以及地气系统的能量收支研究,尤其是目前研究较多的云和沙尘等大粒子气候效应有重要意义。     

SBDART的参数化短波辐射传输模型

云层对地气系统辐射能量平衡有重要的调节作用,然而传统1维大气辐射传输模型仅能考虑晴空和全云两种情况。为了更好地研究云层对地表短波辐射的影响,以大气辐射传输模型SBDART(Santa Barbara Disort Atmospheric Radiative Transfer)为基础,在短波辐射传输基本方程中引入半球天空有效云覆盖度和区域真实云覆盖度两个关键云参数,考虑太阳方向和半球天空云层覆盖情况,对模型进行几何关系的修正。结合短波辐射的影响因素和SBDART模型的内置参数,选择13个参数,使用全局定量敏感性分析软件Sim Lab对修正后的模型进行参数敏感性分析及应用讨论。研究结果表明:该模型能够较好地描述云层对地表短波辐射的影响;对下行短波辐射和地表短波净辐射而言,太阳天顶角和地表反照率的影响最为显著;两个云覆盖参数在很大程度上也影响了地表短波辐射分量;在模型实际应用过程中,敏感性较强的6个参数均可以通过卫星遥感数据得到,模型具有较好的应用前景。由此可见,改进的短波辐射传输模型能够更好地考虑不同云层条件下、不同太阳–云–观测几何下的短波辐射传输问题,有利于提高短波辐射参量的遥感反演精度。     

The cloud phase discrimination from a satellite

A new technique to identify mixed-phase clouds but also clouds with supercooled water droplets using satellite measurements is proposed. The technique is based on measurements of the backscattered solar light at wavelengths 1.55 and 1.67 /spl mu/m in combination with cloud brightness temperature measurements at 12 /spl mu/m. For the first time, the concept of the phase index-temperature correlation plot (the P-T diagram) is introduced in the cloud remote sensing. Retrievals of cloud temperature and cloud phase index are performed using data from the Advanced Along Track Scanning Radiometer (AATSR) and Scaning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) both onboard the Envisat platform.     

风云三号卫星被动微波反演海洋上空云液态水含量

云液态水含量是气候和水循环研究的重要云微物理参数，也是目前气候变化研究中的最不确定因素之一。通过极轨气象卫星被动微波观测的光谱和极化特征能够实现对云液态水含量的直接测量，本文介绍了一种基于风云三号卫星微波成像仪（MWRI）观测亮温的全天候云液态水含量反演算法，利用快速辐射传输模式、云模型和大气廓线库建立MWRI模拟亮温库并训练反演系数的宽气候态物理算法可以保证算法系数在不同季节和不同地区的适应性。同时提出了一种基于观测增量（O-B）筛选晴空像元并对算法系数及比例因子进行订正的方法。利用统计直方图方法和卫星间交叉比对方法对反演产品精度进行了检验，统计直方图方法检验结果表明，FY-3C云水反演误差为0.028 mm，FY-3D为0.025 mm，与国外同类产品的精度相当；与低轨卫星微波辐射计GMI云水产品的交叉比对结果表明，两者具有较高一致性，均方根误差为0.0325 mm。FY-3C/3D CLW产品目前已经投入业务应用，上下午星组网能够一天内基本覆盖全球，实现全球云水分布监测。     

利用云下阴影实现陆地上空气溶胶和地表反射率的同时反演—理论方法和模拟

卫星探测信号包含大气中分子和粒子的散射贡献以及地表反射的贡献,在陆地上空二者的贡献相当,并且陆地地表反射率在时间和空间上极度不均一,因此,很难区分二者的各自贡献从而定量提取大气气溶胶和地表反射率,陆地上空气溶胶的反演也一直是一个极具挑战性的课题.而高分辨率卫星资料如TM5的可见光通道能够很好地区分云和云下阴影,如果云是不透光的,在阴影上空,卫星信号仅包含大气散射贡献和地表漫反射贡献,而在邻近的非阴影区上空,卫星探测信号还包含地表直接反射的贡献,根据这个原理,利用辐射传输模式分析了阴影区和非阴影区上空卫星探测的辐射量差别与地表反射率和大气气溶胶的关系,提出一种利用云下阴影来同时提取阴影上空大气气溶胶和地表反射率的单波长反演方案,并对气溶胶单次散射反照率,散射相函数,测量精度以及地表反射率的不均一性进行了敏感性分析.     

利用SeaWiFS数据反演海岸地物光谱反射率

提出了一个利用SeaWiFS数据反演气溶胶光学厚度与沿岸地物光谱反射率的迭代算法.该算法借助于6S辐射传输模型,利用水色卫星的近红外通道由水体像元首先反演出0.55μm波段的气溶胶光学厚度,在所选影像晴空无云的条件下假定沿岸陆地上空的大气条件与水体上空的大气条件相同,然后再迭代计算出沿岸地物光谱反射率.给出了实际卫星数据计算的结果,并对可能出现的非清洁水体与气溶胶对时空变化引起的误差进行了数值模拟.     

中国北方地区春季气溶胶光学特性地基遥感研究

基于中国北方地区地基太阳直接/散射辐射计观测,分析了2001年春季气溶胶光学厚度、尺度和吸收特性。沙尘期间,气溶胶光学厚度显著升高,而尺度上升,粗粒子浓度显著增加,大气气溶胶表现出中性或异常消光特征。除沙尘活动之外,中国华北地区人为排放也是导致气溶胶光学厚度偏高的一个重要原因。中国沙尘源区气溶胶单次散射反照率小于以往观测和模式结果。北京和香河两地气溶胶光学厚度、Angstrom指数和尺度谱基本相似,说明华北地区人为排放与沙尘活动类似,也表现出区域尺度的特点。由于沙尘气溶胶与人为排放气溶胶相比,折射指数实部偏大、虚部偏小,从而北京地区沙尘期间单次散射反照率明显大于非沙尘期间,特别是在近红外波段,说明沙尘活动不仅可以通过增加气溶胶光学厚度,同时也通过改变气溶胶物理、辐射特性来影响下游地区的气溶胶辐射强迫。     

海冰微波辐射的数值模式和遥感实验测量

本文用多频段微波辐射计(1.4,3.09,5.4,36 GHz)对辽东湾和渤海湾的海冰热辐射进行了遥感测量。海冰模拟为一层介电强起伏的各向异性的随机介质。求解随机介质的辐射传输方程,得到海冰的辐射亮度温度。数值计算的结果与实验数据进行了比较,并对辐射亮度温度和海冰各种参数之间的函数关系进行了讨论。     

基于葵花-8卫星大气产品的地表下行短波辐射计算

地表下行短波辐射DSSR(Downward Surface Shortwave Radiation)的准确估算在气候变化研究和地表太阳能估算等领域具有重要作用。新一代静止气象卫星葵花-8(Himawari-8)具有高达10 min的对地观测能力,为DSSR近实时估算提供了新机遇。然而,日本宇宙航空研究开发机构(JAXA)对外公开的葵花-8辐射产品中,没有将其反演的云、气溶胶产品作为DSSR的输入参数,从而没有形成一整套的DSSR估算算法流程,缺乏产品输出的一致性。大气中的云、气溶胶是DSSR的重要影响因子,本文重点考虑云、气溶胶对太阳辐射的影响,基于大气辐射传输模式RSTAR构建了DSSR查找表,开发了DSSR的快速计算方法,进而将JAXA葵花-8二级云、气溶胶产品(光学厚度,粒子有效半径等)作为快速化计算方法的输入参量,计算得到了DSSR。通过与JAXA葵花-8二级DSSR产品(JAXA DSSR)对比,发现两者具有很好的空间一致性。为了进一步评价本文的DSSR计算精度,分别选取了陆地(Yonsei)和海洋(0n_165e)的观测数据验证了2016年4、7、10和12月本文计算的DSSR和同时期的JAXA DSSR产品,验证结果显示两者的DSSR在两个观测站点均具有非常高的相关性(全天空、晴空和云天条件下的相关系数R均大于0.88)。在两个站点云天条件下的验证结果中,考虑了云相态并在冰云模型中使用了非球形冰晶粒子(六棱柱)来计算DSSR,获得了比JAXA DSSR更小的偏差。本文提出的快速化计算方法能快速准确地计算DSSR,可为计算地表辐射收支等研究提供重要数据支撑。     

Comparison of Three Years of Terra and Aqua MODIS Aerosol Optical Thickness Over the Global Oceans

Far from land-based sources, long-term statistics of aerosol optical thickness (AOT) over the oceans is expected to have a negligible diurnal signal. Therefore, comparing large-scale regional and global mean AOT derived independently from Terra and Aqua Moderate Resolution Imaging Spectroradiometer data will provide a measure of the precision of the overall product. Three years of overlapping records of quality and pixel-weighted level-3 statistics were analyzed. These data show that the instruments' measurement of the long-term global annual mean agree to within 1% or 0.0014-in optical thickness with an rms difference of 0.004, which is calculated from global monthly means. Two-thirds of the regions have long-term annual regional means that agree to within 2.5%. The highest regional difference is 5%, which is found over the southern circumpolar ocean. Other aerosol parameters such as particle size will show larger differences. Datasets that are not quality and pixel weighted may also show larger differences     

POLDER-2PARASOL卫星气溶胶业务产品在北京地区的验证分析

利用地面AERONET/PHOTONS气溶胶观测网北京和香河站点的资料,在北京地区对POLDER12/PARAsOL卫星多角度偏振信息获得的气溶胶反演产品进行了验证分析.地基AERONET/PHOTONS观测网的体积谱分布资料分析显示,在北京地区气溶胶尺度分布的细粒子截断半径约为0.3um.将POLDER-2/PARASOL卫星气溶胶业务产品和重新定义的地基AERONET/PHOTONs细模态(半径r<0.3p.m)气溶胶光学厚度(AOT)比较,两者在北京地区有着很好的一致性,说明卫星的气溶胶业务反演产品表征了主要来自人类污染排放的细粒子气溶胶贡献.然而,由于POLDER系列卫星业务反演方法固定了埃斯屈朗(Angstrom)指数的变化范围是1.8-3.0造成了细粒子贡献占绝对主导的局限.由地基AERONET/PHOTONS观测资料的分析可知,这个埃斯屈朗指数的先验值远远大于北京地区的地基测量结果,导致了POLDER业务反演的气溶胶光学厚度偏低,埃斯屈朗指数偏高.     

A new algorithm to retrieve aerosol over the gulf of cambay in India

Ocean color analysis and aerosol retrieval in coastal regions are made difficult by water turbidity. An algorithm has been proposed which uses the data at a blue wavelength instead of those in near-infrared wavelengths for the aerosol retrieval. The quasi-homogeneous effects are assumed for the correction of water leaving radiance with soil particles at 0.412 μm. The proposed algorithm is examined using SeaWiFS data on December 24, 2000 around India. Over the coastal waters, extremely large values of optical thickness are extracted from the operational SeaWiFS algorithm, whereas our proposed algorithm produces a smooth transition in values of optical thickness from the turbid waters to the surrounding regions.     

Is There a Physical Linkage Between Surface Emissive and Reflective Variables Over Non-Vegetated Surfaces?

For a satellite sensor with only one or two thermal infrared channels, it is difficult to retrieve the surface emissivity from the received emissive signal. Empirical linear relationship between surface emissivity and red reflectance are already established for deriving emissivity, but the inner physical mechanism remains unclear. The optical constants of various minerals that cover the spectral range from 0.44 to 13.5 μm in conjunction with modern radiative transfer models were used to produce corresponding surface reflectance and emissivity spectra. Compared to the commonly used empirical linear relationship, a more accurate multiple linear relationship between Landsat TM5 emissivity and optical reflectances was derived using the simulated data, which indicated the necessity of replacing the empirical relationship with the new one for improving surface emissivity estimate in the single channel algorithm. The significant multiple linear relationship between broadband emissivity (BBE, 8–13.5 μm) and MODIS spectral albedos was also derived using the same data. This paper demonstrates that there is a physical linkage between surface emissive and reflective variables, and provides a theoretical perspective on estimating surface emissivity for sensors with only one or two thermal infrared channels.     

Modelling of radiation transfer in Earth’s hazy atmosphere and calculation of path radiances in IRS LISS-I Bands

A model (named ATMRAD) of radiation transfer in the Earth’s hazy atmosphere based on simplistic solution of radiation transfer equation and tropical model atmosphere is developed to estimate path radiance for correction of remote sensing multispectral data. The atmosphere is assumed to be cloud free and plane-parallel stratified with various quatities specified for 46 layers in its 100 km assumed thickness and model altitude profiles of haze aerosols specified for 23 km and 5 km visibility ranges. Altitude profiles of haze for any intermediate visibility ranges are deduced from linear mixing of the two profiles for 23 and 5 km visibilities. Deirmendjian size distribution function is assumed for aerosols. The radiation transfer calculations have been performed for 126 wavelengths in 0.25 to 3.0 μm range by considering Rayleigh and Mie Scatterings by air molecules and aerosols; and absorption by atmospheric gases. The model calculations have been carried out for path radiances in bands of IRS LISS-I sensor for different visibility ranges and solar illumination angles.     

三种国际主流的北极卫星遥感冰速产品评估和分析

冰速是海冰的重要参数,但是受资料长度限制,对卫星遥感冰速产品进行系统比较和评估的研究还较少。利用2009年—2017年国际北极浮标计划（IABP）浮标冰速数据,较系统地评估了不同时间间隔的遥感反演冰速产品在北冰洋内区和弗拉姆海峡附近海区的表现。结果显示,对北冰洋内区而言,1 d间隔的美国国家雪冰数据中心（NSIDC）遥感冰速冬季误差整体大于夏季,冬季高估了波弗特海南部海冰向西的运动,低估了从喀拉海流向格陵兰岛北部的穿极流。对于5种2 d间隔冰速产品而言,产品精度不完全取决于源数据空间分辨率的高低,反演算法的改进和数据融合均能提高冰速的精度,均方根误差大小的顺序是OSISAF-Merged <OSISAF-AMSR <Ifremer-AMSR <OSISAF-SSM < OSISAF-ASCAT。对于4种使用相同反演算法的3 d间隔的冰速产品,产品的均方根误差取决于源数据分辨率,空间分辨率最高的Ifremer-AMSR冰速均方根误差最小。比较不同种类、不同时间间隔冰速的月平均均方根误差后可知,采用3 d间隔反演的冰速由于能够忽略更多短时间尺度海冰运动,其冰速均方根误差低于2 d间隔的冰速。在弗拉姆海峡,除Ifremer-AMSR外,其余冰速产品均具有较大的经向偏差和均方根误差。在冰速较快弗拉姆海峡,冰速产品均方根误差取决于源数据的分辨率。     

MODIS大气产品的光合有效辐射估算研究

利用气溶胶、水汽、云以及臭氧等MODIS标准大气产品,在简单辐射传输模型基础上估算青藏高原光合有效辐射,经验证估算的光合有效辐射与实测数据存在显著的线性相关,相关系数在0.8—0.9之间,最大误差为13%。经过敏感性分析发现云层厚度、气溶胶含量以及大气压力对光合有效辐射的影响大。臭氧和水汽含量的变化不敏感。云层厚度、Angstrom浑浊度系数和大气压力分别变化30%、25%和15%时,光合有效辐射变化分别为20%、5%和5%。