Assessing global Sentinel-2 coverage dynamics and data availability for operational Earth observation (EO) applications using the EO-Compass     

Martin Sudmanns  Dirk Tiede  Hannah Augustin  Stefan Lang 《International Journal of Digital Earth》2020,13(7):768-784

ABSTRACT

Sentinel-2 scenes are increasingly being used in operational Earth observation (EO) applications at regional, continental and global scales, in near-real time applications, and with multi-temporal approaches. On a broader scale, they are therefore one of the most important facilitators of the Digital Earth. However, the data quality and availability are not spatially and temporally homogeneous due to effects related to cloudiness, the position on the Earth or the acquisition plan. The spatio-temporal inhomogeneity of the underlying data may therefore affect any big remote sensing analysis and is important to consider. This study presents an assessment of the metadata for all accessible Sentinel-2 Level-1C scenes acquired in 2017, enabling the spatio-temporal coverage and availability to be quantified, including scene availability and cloudiness. Spatial exploratory analysis of the global, multi-temporal metadata also reveals that higher acquisition frequencies do not necessarily yield more cloud-free scenes and exposes metadata quality issues, e.g. systematically incorrect cloud cover estimation in high, non-vegetated altitudes. The continuously updated datasets and analysis results are accessible as a Web application called EO-Compass. It contributes to a better understanding and selection of Sentinel-2 scenes, and improves the planning and interpretation of remote sensing analyses.  相似文献   

基于RegCM4.6的中国地区云对地表太阳辐射的影响研究     

郭子嘉  刘鑫  陈勇航  辛渝  张蕾  秦艳  陈春美  刘平平  周海江 《沙漠与绿洲气象(新疆气象)》2020,14(6):107-113

使用RegCM4.6区域气候模式，选取Emanuel和Mix（Grell+Emanuel）两种积云对流参数化方案，以2016年为例，分别对中国地区云短波辐射强迫及其涉及的物理量进行数值模拟，揭示其时空分布特征，并探究两种积云对流参数方案模拟效果的差异及其原因。结果表明：从季节平均来看，全国地表云短波辐射强迫均为负值，云对地表为冷却效应，冬季最小，春夏季较大。塔里木盆地四季均为辐射强迫低值区，夏季冷却效应最弱，辐射强迫绝对值低于40 W·m-2；全天空地表净短波辐射分布也呈显著季节差异，除夏季外均呈由南向北逐渐递减的分布趋势；晴空地表净短波辐射在横断山脉处和塔里木盆地处均比较低，其中春季最为明显；两个方案所得的季节空间分布特征大致相同，但在数值上存在差异。春季时全国大部分地区全天空地表净短波辐射通量差异最大，在55 W·m-2左右，晴空地表净短波辐射通量在青藏高原处差异在60W·m-2左右。  相似文献   

The Vertical Transport of Air Pollutants by Convective Clouds. Part I: A Non-Reactive Cloud Transport Model   总被引：1，自引：0，他引：1  

Kong Fanyou  Qin Yu 《大气科学进展》1993,10(4):415-427

A convective cloud transport model, without chemical processes, is developed by joining a set of concentration conservative equations into a two-dimensional, slab-symmetric and fully elastic numerical cloud model, and a numerical experiment is completed to simulate the vertical transport of ground-borne, inert gaseous pollutant by deepthunderstorm. The simulation shows that deep convective storm can very effectively transport high concentrated pollutant gas from PBL upward to the upper troposphere in 30 to 40 minutes, where the pollutant spreads laterally outward with strong anvil outflow, forming an extensive high concentration area. Meanwhile, relatively low concentration areas are formed in PBL both below and beside the cloud, mainly caused by dynamic pumping effect and sub-cloud downdraft flow. About 80% of the pollutant gas transported to the upper troposphere is from the layer below 1.5 km AGL (above ground level).  相似文献   

台湾地区中尺度试验期间梅雨锋及其对流云团的研究   总被引：2，自引：1，他引：2       下载免费PDF全文

马群飞  赵思雄 《大气科学》1993,17(2):173-184

本文对台湾地区中尺度试验(TAMEX)中的两次IOP(加密观测期)过程进行了诊断研究,结果表明: (1)1987年5月13日至17日,台湾地区的对流系统活跃.究其原因,主要系两次锋面过境所致.这两条锋面的温度梯度比长江流域一般的梅雨锋要强.梅雨锋上的对流云团与降水直接有关. (2)高空东移短波槽与梅雨锋的有利配合,是造成台湾地区出现较大降水的重要原因、IOP2有高空短波槽配合,因而降水比IOP1大、槽与锋面的配合,使对流层中低层正涡度区加强,这与华南前汛期暴雨的特征有某些相似之处。 (3)由每小时一次的GMS卫星云图上发现,在此期间台湾地区发展的对流云团与大陆的系统联系密切.此外,NCAR飞机落仪探测资料表明,与环境相比,云团内部有较深厚的湿层;时空加密探空资料的计算结果显示,700hPa以下的水汽主要来自水平方向的辐合,而在高层主要来自垂直输送.对于活跃的云团而言,上述特征更加明显.  相似文献   

不同的大气云模式对月预报影响的数值试验   总被引：1，自引：0，他引：1  

郑庆林  蒋平  吴军 《应用气象学报》1993,(Z1)

所用的 T42L10月长期数值预报谱模式采用了模式诊断云方案,在辐射计算中,用模式的预报水汽场和模式诊断云代替原民T42L9中的气候纬向平均水汽场和云,模式诊断云计算中还考虑了大地形作用对云的影响.本文利用国家气象中心1992年8月31日的客观分析资料为初始场,进行30天长期数值预报,对比研究了这两种不同的云模式对月际数值预报的影响.模式诊断云方案的预报明显优于气候云方案,采用模式诊断云预报的500hPa 高度场月平均的倾向相关系数有所提高,月平均预报误差减少.模式诊断云方案的预报误差低于对应的持续性误差.模式诊断云方法由于考虑了在预报时间内云分布的时间和空间变化,提高了模式中的辐射计算精度,从而改进模式中的云、辐射作用,克服由于气候云方法所出现的预报偏差,较显著地改善月际数值预报效果.  相似文献   

Phase partitioning of aerosol particles in clouds at Kleiner Feldberg     

A. Hallberg  K. J. Noone  J. A. Ogren  I. B. Svenningsson  A. Flossmann  A. Wiedensohler  H. -C. Hansson  J. Heintzenberg  T. L. Anderson  B. G. Arends  R. Maser 《Journal of Atmospheric Chemistry》1994,19(1-2):107-127

The partitioning of aerosol particles between cloud droplets and interstitial air by number and volume was determined both in terms of an integral value and as a function of size for clouds on Mt. Kleiner Feldberg (825 m asl), in the Taunus Mountains north-west of Frankfurt am Main, Germany. Differences in the integral values and the size dependent partitioning between two periods during the campaign were observed. Higher number and volume concentrations of aerosol particles in the accumulation mode were observed during Period II compared to Period I. In Period I on average 87±11% (±one standard deviation) and 73±7% of the accumulation mode volume and number were incorporated into cloud droplets. For Period II the corresponding fractions were 42±6% and 12±2% in one cloud event and 64±4% and 18±2% in another cloud event. The size dependent partitioning as a function of time was studied in Period II and found to have little variation. The major processes influencing the partitioning were found to be nucleation scavenging and entrainment.  相似文献   

Computer modelling of clouds at Kleiner Feldberg     

R. N. Colvile  R. Sander  T. W. Choularton  K. N. Bower  D. W. F. Inglis  W. Wobrock  D. Schell  I. B. Svenningsson  A. Wiedensohler  H. -C. Hansson  A. Hallberg  J. A. Ogren  K. J. Noone  M. C. Facchini  S. Fuzzi  G. Orsi  B. G. Arends  W. Winiwarter  T. Schneider  A. Berner 《Journal of Atmospheric Chemistry》1994,19(1-2):189-229

The airflow, cloud microphysics and gas- and aqueous-phase chemistry on Kleiner Feldberg have been modelled for the case study of the evening of 1 November 1990, in order to calculate parameters that are not easily measured in the cloud and thus to aid the interpretation of the GCE experimental data-set. An airflow model has been used to produce the updraught over complex terrain for the cloud model, with some care required to ensure realistic modelling of the strong stable stratification of the atmosphere. An extensive set of measurements has been made self-consistent and used to calculate gas and aerosol input parameters for the model. A typical run of the cloud model has calculated a peak supersaturation of 0.55% which occurs about 20 s after entering cloud where the updraught is 0.6 m s^–1. This figure has been used to calculate the efficiency with which aerosol particles were scavenged; it is higher than that calculated by other methods, and produces a cloud with slightly too many droplets. A broad cloud droplet size spectrum has been produced by varying the model inputs to simulate turbulent mixing and fluctuations in cloud parameters in space and time, and the ability of mixing processes near cloud-base to produce a lower peak supersaturation is discussed. The scavenging of soluble gases by cloud droplets has been observed and departures from Henry's Law in bulk cloud-water samples seen to be caused by variation of pH across the droplet spectrum and the inability of diffusion to adjust initial distributions of highly soluble substances across the spectrum in the time available. Aqueous-phase chemistry has been found to play a minor role in the cloud as modelled, but circumstances in which these processes would be more important are identified.  相似文献   

基于神经网络B—P算法的雹云识别模型及其效果检验   总被引：2，自引：7，他引：2  

李祚泳  邓新民 《高原气象》1994,13(1):44-49

本文根据成都、内江和泸州等地的雷达回波和部分探空资料，应用神经网络Ｂ－Ｐ算法建立了不同地区的３参数和４参数雹云识别模型，并对模型进行了分析和效果检验。结果表明：该模型不仅能得到较高的拟合率和预报准确率，而且由于Ｂ－Ｐ网络具有自组织，自学习和自适应的能力，与其它方法相比具有一定的优越性。  相似文献   

气溶胶核化清除的化学效应 I：云滴化学非均匀性的研究     

刘小红  洪钟祥  王明康 《大气科学》1994,18(4):385-395

本文将水汽在云滴上凝结增长的物理过程与气溶胶、气体的化学过程相结合，对气溶胶核化清除的化学效应进行了研究。 计算结果表明:气溶胶的核化清除造成了云滴化学成分随云滴大小分布的非均匀性，这种非均匀性又对云滴内发生的气体吸收、液相氧化产生影响。 本文还比较了不同污染状况下，不同大小的云滴内气溶胶核化清除与液相氧化对云滴化学的相对贡献的差异。 因此，这种云滴化学的非均匀性(云微化学)的研究对于云化学的野外观测及数值模拟都是重要的。  相似文献   

环工作面三维直流电阻率法研究及应用          下载免费PDF全文

高卫富  翟培合  肖乐乐  刘天浩 《地球物理学报》1954,63(9):3534-3544

本文在矿井直流电法理论基础上,推导环工作面三维直流电法测量深度公式,得到环工作面三维直流电法记录点坐标位置.基于以上理论,建立了环工作面三维直流电法异常体模型,分析了环工作面三维直流电法二极装置、三极装置、四极装置异常体响应特征,得出环工作面三维直流电法各装置敏感度低的主要原因是缺少必要的数据采集点.为了提高环工作面三维直流电法分辨率,最大限度增加工作面内侧的采集数据点.基于以上原因本文提出了对角偶极装置采集模式及多装置的数据叠加反演处理方法,以增加工作面内采集数据点,提高三维勘探的精度.本文通过某矿8802工作面底板富水性探查实例,说明该方法的有效性.  相似文献