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.     

The influence of thermodynamic phase on the retrieval of mixed-phase cloud microphysical and optical properties in the visible and near-infrared region

Cloud microphysical and optical properties are inferred from the bidirectional reflectances simulated for a single-layered cloud consisting of an external mixture of ice particles and liquid droplets. The reflectances are calculated with a rigorous discrete ordinates radiative transfer model and are functions of the cloud effective particle size, the cloud optical thickness, and the values of the ice fraction in the cloud (i.e., the ratio of ice water content to total water content). In the present light scattering and radiative transfer simulations, the ice fraction is assumed to be vertically homogeneous; the habit (shape) percentage as a function of ice particle size is consistent with that used for the Moderate Resolution Imaging Spectroradiometer (MODIS) operational (Collection 4 and earlier) cloud products; and the surface is assumed to be Lambertian with an albedo of 0.03. Furthermore, error analyses are performed that pertain to the inference of the mixed-phase cloud effective particle size and optical thickness. Errors are calculated with respect to the assumption of a cloud containing solely liquid or ice phase particles. The analyses suggest that the effective particle size inferred for a mixed-phase cloud can be underestimated (or overestimated) if pure liquid phase (or pure ice phase) is assumed for the cloud, whereas the corresponding cloud optical thickness can be overestimated (or underestimated).     

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。     

Spectroradiometric requirements for the reflective module of the airborne spectrometer ARES

The Airborne Reflective/Emissive Spectrometer is specified as a whisk-broom imaging spectrometer for remote sensing of land surfaces covering the wavelength regions 0.47-2.45 /spl mu/m and 8-12 /spl mu/m with 160 spectral bands. The instrument is being built by Integrated Spectronics, financed by the German Aerospace Agency (DLR) and the GeoResearch Centre Potsdam (GFZ) and will be available to the scientific community from end 2005 on. The spectroradiometric design is based on scientific requirements derived from three main application scenarios comprising vegetation, soil, and mineral sciences. Two of these are described in this letter. Measured or modeled reflectance spectra are input to a simulation model that calculates at-sensor radiance spectra, resamples them with the channel-specific response functions, adds different amounts of noise in the radiance domain, and performs a retrieval to get the corresponding noisy surface reflectance spectra. The retrieval results as a function of the sensor noise level are compared with the accuracy requirements imposed by the different application fields taking into account the technical boundary conditions. The final specifications account for the most demanding requirements of the three application fields: a spectral sampling distance of 13-14 nm in the 470-1800 nm region, and 12 nm in the 2000-2450-nm region. The required noise-equivalent radiances are 5, 3, and 2 nW/spl middot/cm/sup -2//spl middot/sr/sup -1//spl middot/nm/sup -1/ for the spectral regions 470-1000, 1000-1800, and 2000-2450 nm, respectively.     

基于CryoSat-2数据的海冰厚度估算算法比较

以北极为研究区,使用CryoSat-2数据,利用现有海冰厚度卫星测高研究中4种主流算法(Laxon03算法、Kurtz09算法、Yi11算法和Laxon13算法)分别对北冰洋海冰厚度进行估算,并将估算结果与研究区IceBridge机载激光测高冰厚数据进行了比较,探索各算法海冰厚度估算的差异,寻找最优的估算算法,为估算长时序海冰厚度提供基础和参考。结果表明,4种算法估算的海冰厚度空间分布较为一致,但不同算法估算的结果差异较大,可达0.476 m;4种算法估算结果大小依次为Laxon03算法、Yi11算法、Laxon13算法、Kurtz09算法;4种算法估算的平均海冰厚度差异,在北极波弗特海海域最大,其次是北极中心海域、格陵兰和挪威海;Laxon13算法估算结果相对于IceBridge观测结果与其他算法相比,具有最小的平均偏差和均方根误差,是卫星测高估算海冰厚度的最优算法。     

利用CryoSat-2测高数据研究南极威德尔海海冰出水高度时空变化

为了提高南极海冰出水高度的估算精度,以威德尔海为例,基于CryoSat-2卫星测高数据,联合冰桥计划(IceBridge)机载测高数据和科考船走航观测数据,获取应用最低点高程法反演海冰出水高度的最佳估计参数,进而估算并分析了 2011-2017年,每年5月-10月威德尔海海冰出水高度的时空变化.结果表明,最佳的出水高度...     

利用TM数据快速提取含矿蚀变带方法研究

热液蚀变岩类是在含矿热液作用下引起原岩化学成分和物理性质发生变化的结果，因此蚀变岩类往往与内生产矿产伴生，有时其本身就是含矿体。不同蚀变矿特级组合具有独特的光谱响应，但是光谱的反射和吸收产特征较弱称为遥感找矿弱信息标志。     

基于SIA理论的冰川储量计算

本文以抗物热冰川、古仁河口冰川、乌鲁木齐河源1号冰川和东绒布冰川为例,基于SIA理论和数字高程模型(DEM)数据及冰川矢量数据,计算各条冰川主流线的平均厚度值,并利用内插方法得到各条冰川的冰储量。结果表明:①抗物热冰川、古仁河口冰川、乌鲁木齐河源1号冰川和东绒布冰川的储量分别为0.022、0.026、0.024和1.450 km³。②经与传统冰储量计算经验公式、探地雷达(GPR)实测数据计算的冰储量结果相比,基于SIA模型得到的冰储量结果均较小,这与数字高程模型数据精度及断面划分有一定相关性。     

不同钾素处理春玉米叶片营养元素含量变化及其光谱响应

目的是研究不同钾营养水平春玉米典型生育期叶片的光谱响应,探索叶片内营养成分与叶片光谱反射率的相关性。方法是设置了不同梯度钾处理的盆栽试验,按玉米生育期进行光谱测定和取样分析。结果,通过对不同钾处理间玉米叶片养分含量的差异性分析表明,随着施钾的提高,叶片钾含量差异性达到显著水平。分析不同钾营养水平不同生育时期春玉米叶片光谱反射率与叶片钾含量的相关关系,并建立了喇叭口期利用叶片光谱反射率估测叶片钾含量的数学模型;以及分析了该处理下喇叭口期叶片内水分、叶绿素、氮、磷、钙、镁、锌、锰、铜、铁含量与叶片光谱反射率的相关性。结果表明：不同生育时期叶片钾含量与其光谱反射率的相关关系在光谱维方向存在明显差别,730—930nm和960—1100nm两波段为春玉米喇叭口期评价钾营养状况的敏感波段,光谱变量R767＋R1057,（R767＋R1057） /（logR767＋logR1057）和（R767-R1057） /（logR767-logR1057）均能很好的预测喇叭口期叶片钾含量;该时期叶片内不同成分与光谱反射率相关分析表明：550nm,710nm,950nm三波段处是各个相关曲线的突变点;叶片内各成分间高度相关的,它们的光谱相关曲线趋势也极为一致或对称。     

Potential to estimate the canting angle of tilted structures in clouds from microwave radiances around 183 GHz

The effects of cloud structures on microwave radiances at frequencies from 89-190 GHz are investigated by simulations using the Goddard cumulus ensemble model data as input for a radiative transfer model. It was found that the brightness temperatures at these frequencies have different sensitivities to clouds with a tilted structure. The different sensitivities to altitude and amount of hydrometeors allow the estimation of the canting angle and tilt direction of tilted clouds using brightness temperatures at the water vapor channels at 183.3 /spl plusmn/ 1 and 183.3 /spl plusmn/ 7 GHz. The estimated canting angle and tilt direction are in agreement with the model situation. This method provides a potential to estimate tilted convective structures from microwave radiometric observations at 183.3 /spl plusmn/ 1 and 183.3 /spl plusmn/ 7 GHz. It is applied to a tilted storm observed from the National Aeronautics and Space Administration's ER-2 aircraft flying at about 20 km on August 26, 1998 during the third Convection and Moisture Experiment using the observed downlooking brightness temperatures at the water vapor channels of a Millimeter-wave Imaging Radiometer. The estimated results are in good agreement with the realistic storm situation obtained from the simultaneous observations of the ER-2 Doppler radar. This method also provides information about the vertical displacement of cloud structure and thereby to estimate the accurate location of surface rainfall. This is important when validating precipitation retrieval based on observations of the ice scattering above surface rainfall against surface rain observations using the microwave frequencies sensitive to high altitudes.     

增强型多时相云检测

针对云检测在高亮度地表以及雪覆盖区域存在过度检测的问题,设计了一种不依赖热红外波段的增强型多时相云检测EMTCD(Enhanced Multiple Temporal Cloud Detection)算法。首先,利用云的光谱特征建立单时相云检测规则,并基于云、雪的光谱差异构建了增强型云指数ECI(Enhanced Cloud Index),改进了云、雪的区分能力;其次,以同一区域无云影像为参考,基于ECI指数构建了多时相云检测算法,较好地克服了单时相云检测中高亮度地表、雪和云容易混淆的问题,提高了云检测的精度;最后,选择两个典型区域的Landsat-8 OLI影像,对比分析了不同算法的云检测结果。实验结果表明:ECI指数能够有效区分云、雪,EMTCD方法的平均检测精度达到93.2%,高于Fmask(Function of mask)(81.85%)、MTCD(Multi-Temporal Cloud Detection)(66.14%)和Landsat-8地表反射率产品LaSRC(Landsat-8 Surface Reflectance Code)的云检测结果(86.3%)。因此,本文提出的EMTCD云检测算法能够有效地减少高亮度地表和雪的干扰,实现不依赖热红外波段的高精度云检测。     

Dust Radiative Effects Over Global Oceans

Using one year of moderate resolution imaging spectroradiometer (MODIS) and clouds and the Earth's radiant energy system (CERES) data, we provide a satellite-based assessment of top-of-atmosphere (TOA) cloud-free shortwave and longwave dust radiative effects over global oceans from the Terra satellite. Over global cloud-free oceans, the dust net radiative effect is -0.7 plusmn0.2 W middotm^-2, and the TOA dust shortwave radiative effect (SWRE) dominates the longwave radiative effect (LWRE). Globally, the annual mean dust contribution to the total MODIS level 2 aerosol optical thickness (AOT, at 550 nm) is about 30% with a dust SWRE of -0.7 plusmn0.2 W middotm^-2 and LWRE of 0.03 plusmn0.02 W middotm^-2. Averaged over all seasons, the cloud-free diurnal mean dust radiative efficiency is -33 plusmn5 W middotm^-2 middottau^-1, and there is a remarkable linear relationship between the CERES SWRE and the MODIS AOT. This is the first satellite-based assessment of dust net radiative effect over the global oceans and will serve as a useful constraint for numerical modeling analysis.     

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     

植被稀疏地区沟蚀变化的地面激光扫描监测与沟蚀量估算

针对传统沟蚀监测手段劳作强度大,且数据采集的完整性、代表性受切沟复杂地形制约等问题,提出了一种针对植被稀疏地区沟蚀变化的地面激光扫描（terrestrial laser scanning,TLS）监测方法,形成了一套数据处理与侵蚀量计算技术流程。以河北省官厅水库东岸某大型切沟为例,利用高精度TLS进行两年3期野外监测与点云数据分析。通过点云配准、滤波、重采样及曲面拟合等预处理,生成不同采样分辨率下3期切沟表面模型,并提取地形信息;采用杨赤中滤波推估法计算并比较不同点云重采样分辨率下的沟蚀量。结果表明:（1）当点云重采样分辨率与切沟表面凹凸微结构暨石块粒径（2~6cm）接近时,沟蚀量估算值趋于稳定、结果可靠;（2）经侵蚀作用,切沟外壁表面高程整体降低2~20 cm;（3）切沟内壁侵蚀量不均衡,坡度较大处侵蚀最为显著。     

利用新型C波段雷达卫星研究南伊内里切克冰川运动特征

利用新型C波段Sentinel-1卫星获取的2015年2月至2017年2月期间的影像数据,研究分析了天山中部南伊内里切克冰川不同时段的运动特征。利用偏移量追踪技术计算不同时间段冰川位移,首先采用三步配准的方法进行主辅影像高精度整体配准,然后基于归一化互相关（normalized cross correlation,NCC）算法通过调整窗口参数精确估算局部偏移量,进一步分离得到冰川移动信息。监测结果表明:（1）在空间分布上,狭长的冰舌区是冰川主要的高速流动区域,冰舌区底部流速小于上部,两侧流速小于中间,末端流速明显减缓。（2）在季节变化上,冰川运动速率与温度变化趋势一致,在5月至8月期间运动速率最快,沿剖面线的最高速率达49 cm/d;在11月至次年2月期间运动最为缓慢,速率为25~30 cm/d左右。（3）在年度变化上,2015年夏季的运动速率比2016年整体高约1~3 cm/d,其他季节则没有明显差异。与高分辨率L波段PALSAR-2影像的监测结果进行定量对比分析时,将冰舌区的像元进行抽稀后统计,得到两种数据获取的运动速率之差的均值为3.48 cm/d,标准差为±3.78 cm/d,证实了南伊内里切克冰川运动监测结果的可靠性。     

“针孔”模拟成像下的单航空影像与LiDAR点云配准

以摄影测量共线方程为严格配准模型,提出了一种引入针孔成像模拟过程的单张航空影像LiDAR点云配准迭代方法,共分为3个阶段:第一,利用航空影像内参数及初始外方位元素对LiDAR点云针孔模拟成像,生成与航空影像空间分辨率、几何形变相接近且具有相同幅面大小的透视影像-LiDAR深度影像;第二,以梯度互信息作为影像相似性测度依据,实施影像金字塔、分块处理策略实现LiDAR深度影像与航空影像几何变换参数快速估计,进而依据估计参数及LiDAR深度影像、激光脚点投影关系建立LiDAR点云航空影像概略相关;第三,以LiDAR点云影像概略相关下的近似同名像点为观测值,以像点梯度互信息为权重,实施摄影测量空间后方交会计算获得优化的影像外方位元素,生成新的LiDAR深度影像并重复上述过程,直至满足给定的迭代计算条件,实现单张航空影像与LiDAR点云数据的自动空间配准。实验表明,本文方法配准精度达亚像素级且自动化程度高。     

融合多光谱影像的高光谱影像厚云去除方法

云遮挡对高光谱影像的应用造成了不可忽视的影响。现有云去除方法通常利用时域近邻的同源影像提供辅助信息。然而,高光谱影像(如GF-5和EO-1高光谱影像)较低的时间分辨率导致同源辅助影像中可能存在较大的地物覆盖变化。时间分辨率更高的多光谱影像(如Landsat 8 OLI影像)能提供时间上更接近于高光谱云影像的辅助信息,从而减少地物覆被变化带来的影响。为应对高光谱和多光谱波段之间差异较大的问题,本文基于空谱随机森林(spatial-spectral-based random forest,SSRF)方法,提出一种利用多光谱影像(Landsat 8 OLI影像)对高光谱影像进行厚云去除的方法,将其简记为SSRF_M。SSRF_M较强的非线性拟合能力使其能够综合利用多光谱影像所有波段的有效数据对各个高光谱波段进行重建。本文使用GF-5和EO-1高光谱影像进行模拟云去除试验,视觉和定量评价结果均表明,与利用时间间隔更长的同源辅助影像的方法相比,本文方法能获得更高精度的云下信息重建结果。     

Effect of raindrop size distribution variability in dual-frequency radar rain retrieval algorithms assessed from disdrometer measurements

The effect of natural variation of raindrop size distribution (DSD)on the retrieval of rainfall rate from the dual-frequency (13.6/35.5 GHz,as will be in the Global Precipitation Measurement Mission) Precipitation Radar (DPR) measurements is studied by utilizing a large set of disdrometer-measured DSD data through a simple simulation framework. A DPR inversion technique(DPR-IT) that focuses on the retrieval of DSD information from the non-Rayleigh backscattering characteristic of the hydrometeors and a conventional DPR technique(DPR-CT) that focuses on the independent retrieval of rainfall rate from the attenuation measurement are considered in this analysis. The preliminary results show that at different rainfall rate regions these methods have different responses to the DSD variability. For instance, it appears that DPR-IT suffers relatively less from the DSD variability in the regions of weak to moderate rainfall rate (/spl bsol/ mm /spl middot/ h/sup -1/),while in the strong rainfall rate (>/spl sim/10 mm /spl middot/ h/sup -1/) region the DPR-CT generally has less sensitivity to DSD variations than the DPR-IT.     

Spatial distribution of altered minerals in the Gadag Schist Belt (GSB) of Karnataka,Southern India using hyperspectral remote sensing data

Spatial distribution of altered minerals in rocks and soils in the Gadag Schist Belt (GSB) is carried out using Hyperion data of March 2013. The entire spectral range is processed with emphasis on VNIR (0.4–1.0 μm) and SWIR regions (2.0–2.4 μm). Processing methodology includes Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes correction, minimum noise fraction transformation, spectral feature fitting (SFF) and spectral angle mapper (SAM) in conjunction with spectra collected, using an analytical spectral device spectroradiometer. A total of 155 bands were analysed to identify and map the major altered minerals by studying the absorption bands between the 0.4–1.0-μm and 2.0–2.3-μm wavelength regions. The most important and diagnostic spectral absorption features occur at 0.6–0.7 μm, 0.86 and at 0.9 μm in the VNIR region due to charge transfer of crystal field effect in the transition elements, whereas absorption near 2.1, 2.2, 2.25 and 2.33 μm in the SWIR region is related to the bending and stretching of the bonds in hydrous minerals (Al-OH, Fe-OH and Mg-OH), particularly in clay minerals. SAM and SFF techniques are implemented to identify the minerals present. A score of 0.33–1 was assigned for both SAM and SFF, where a value of 1 indicates the exact mineral type. However, endmember spectra were compared with United States Geological Survey and John Hopkins University spectral libraries for minerals and soils. Five minerals, i.e. kaolinite-5, kaolinite-2, muscovite, haematite, kaosmec and one soil, i.e. greyish brown loam have been identified. Greyish brown loam and kaosmec have been mapped as the major weathering/altered products present in soils and rocks of the GSB. This was followed by haematite and kaolinite. The SAM classifier was then applied on a Hyperion image to produce a mineral map. The dominant lithology of the area included greywacke, argillite and granite gneiss.     

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。