共查询到20条相似文献，搜索用时 765 毫秒
1.
应用新一代天气雷达数据资料,结合飞机定位播撒,在目标云体上截取一个作业区,同时在作业区两侧设立2个对比区,计算3个区域的雷达强度数值。随着雷达观测的继续,可以得到3条雷达强度随时间变化的曲线。对比分析3条曲线的变化趋势,初步得出：飞行播撒催化剂后,作业区、扩散区较上风方的自然区,雷达回波强度值有明显增强趋势。本文应用2007年12月26日的新一代天气雷达回波数据、雷达站上游气象探空以及人工增雪飞机播撒催化剂的航迹等资料,针对新疆冬季层状云的早期催化效果评估,作者设计了新的检验模式,进行了定量化计算。具体方法为：（1）在雷达的平显气象回波（PPI）上,截取一段飞机播撒催化剂航迹;（2）设定宽10 km的带状航迹为“播撒区”,代表播撒状态下云的演变;上风方宽10 km的区域为“对比区A”,代表自然状态下云的演变;下风方宽10 km的区域为“对比区B”,代表扩散状态下云的演变;（3）分别计算3个区域的雷达回波强度（dbz）总值。随着雷达观测的继续,可以得到雷达回波强度（dbz）随时间变化的3条曲线;（4）对比分析3条曲线的变化趋势,初步得出结论：人工增雪飞机进行播撒催化剂后,作业区及“对比区B”的回波强度总值,比“对比区A”的回波强度总值,有明显地增强趋势。 相似文献
2.
《Polar Science》2007,1(1):17-23
Variations of cloud amount and radiative fluxes are a matter of discussion related to the recent climate change in the Arctic and Antarctic. It is also of great concern related to “from dimming to brightening” recently found. Discussions based on satellite data had been conducted; however, no solid results are obtained from the surface station data for a long term in the recent.At Syowa Station, Antarctica, meteorological observation has been continued for nearly 50 years. During this term, an annual mean cloud amount showed a gradual increase at a rate of 0.014/yr. Radiation budget was observed since 1991 as one of the BSRN stations. Trends of monthly mean radiative fluxes were compared with those of cloud amount and conformable relations were seen during the period from 1991 to 2004. A cloud radiative forcing was estimated. In December, a downward trend in net longwave and net total appeared, while an upward trend in net shortwave was seen, and all corresponded to the decrease of cloud amount in this month. On the other hand in June, an upward trend in net longwave forcing was seen, corresponding to the increase of cloud amount. On an average, cloud radiative forcings at Syowa Station represented those of Antarctic costal stations near sea ice area. 相似文献
3.
Dara E. Seidl Piotr Jankowski Ming-Hsiang Tsou 《International journal of geographical information science》2016,30(4):785-800
Personal trajectory data are increasingly collected for a variety of academic and recreational pursuits. As access to location data widens and locations are linked to other information repositories, individuals become increasingly vulnerable to identification. The quality and precision of spatially linked attributes are essential to accurate analysis; yet, there is a trade-off between privacy and geographic data resolution. Obfuscation of point data, or masking, is a solution that aims to protect privacy and maximize preservation of spatial pattern. Trajectory data, with multiple locations recorded for an entity over time, is a strong personal identifier. This study explores the balance between privacy and spatial pattern resulting from two methods of obfuscation for personal GPS data: grid masking and random perturbation. These methods are applied to travel survey GPS data in the greater metropolitan regions of Chicago and Atlanta. The rate of pattern correlation between the original and masked data sets declines as the distance thresholds for masking increase. Grid masking at the 250-m threshold preserves route anonymity better than other methods and distance thresholds tested, but preserves spatial pattern least. This study also finds via linear regression that median trip speed and road density are significant predictors of trip anonymity. 相似文献
4.
PATMOS-x、ISCCP云量产品及地面观测在中国区域的对比分析 总被引：2，自引：1，他引：1
利用1986~2006年PATMOS-x 、ISCCP总云量和低云量产品与中国区域地面台站观测的总云量、低云量资料进行对比分析,对比不同来源、不同观测方法造成的云量数据在时间、空间上的差异,为资料使用者提供参考。结果表明,与台站观测资料相比,无论PATMOS-x还是ISCCP其总云量数据的空间分布、与站点观测数据的格点相关性均好于低云量数据;PATMOS-x总云量、低云量多年平均的空间分布较ISCCP更接近站点观测;中国区域平均低云量的线性趋势PATMOS-x与站点观测一致,表现为显著的上升趋势,而ISCCP低云量数据则呈现微弱的下降趋势。 相似文献
5.
RICHARD ASPINALL 《International journal of geographical information science》2013,27(2):105-121
Abstract This paper describes an inductive modelling procedure integrated with a geographical information system for analysis of pattern within spatial data. The aim of the modelling procedure is to predict the distribution within one data set by combining a number of other data sets. Data set combination is carried out using Bayes’ theorem. Inputs to the theorem, in the form of conditional probabilities, are derived from an inductive learning process in which attributes of the data set to be modelled are compared with attributes of a variety of predictor data sets. This process is carried out on random subsets of the data to generate error bounds on inputs for analysis of error propagation associated with the use of Bayes’ theorem to combine data sets in the GIS. The statistical significance of model inputs is calculated as part of the inductive learning process. Use of the modelling procedure is illustrated through the analysis of the winter habitat relationships of red deer in Grampian Region, north-east Scotland. The distribution of red deer in Deer Management Group areas in Gordon and in Kincardine and Deeside Districts is used to develop a model which predicts the distribution throughout Grampian Region; this is tested against red deer distribution in Moray District. Habitat data sets used for constructing the model are accumulated frost and altitude, obtained from maps, and land cover, derived from satellite imagery. Errors resulting from the use of Bayes’ theorem to combine data sets within the GIS and introduced in generalizing output from 50 m pixel to 1 km grid squares resolution are analysed and presented in a series of maps. This analysis of error trains is an integral part of the implemented analytical procedure and provides support to the interpretation of the results of modelling. Potential applications of the modelling procedure are discussed. 相似文献
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Paul M. Mather 《International journal of geographical information science》2013,27(5):543-554
Abstract Results of a simulation study of map-image rectification accuracy are reported. Sample size, spatial distribution pattern and measurement errors in a set of ground control points, and the computational algorithm employed to derive the estimate of the parameters of a least-squares bivariate map-image transformation function, are varied in order to assess the sensitivity of the procedure. Standard errors and confidence limits are derived for each of 72 cases, and it is shown that the effects of all four factors are significant. Standard errors fall rapidly as sample size increases, and rise as the control point pattern becomes more linear. Measurement error is shown to have a significant effect on both accuracy and precision. The Gram-Schmidt orthogonal polynomial algorithm performs consistently better than the Gauss-Jordan matrix inversion procedure in all circumstances. 相似文献
8.
Principal components(PCs)for principal component regression(PCR)have historically been selectedfrom the top down for a reliable predictive model.That is,the PCs are arranged in a list starting withthe most informative(PC associated with the largest singular value)and proceeding to the leastinformative(PC associated with the smallest singular value).PCs are then chosen starting at the top ofthis list.This paper discusses an alternative procedure of treating PC selection as an optimization prob-lem.Specifically,without any regard to the ordering,the optimal subset of PCs for an acceptablepredictive model is desired.Five data sets are analyzed using the conventional and alternative approaches.Two data sets are spectroscopic in nature,two data sets deal with quantitative structure-activityrelationships(QSARs)and one data set is concerned with modeling.All five data sets confirm thatselection of a subset without consideration to order secures the best results with PCR.One data set isalso compared using partial least squares 1. 相似文献
9.
Additional Samples: Where They Should Be Located 总被引：2，自引：0，他引：2
Information for mine planning requires to be close spaced, if compared to the grid used for exploration and resource assessment. The additional samples collected during quasimining usually are located in the same pattern of the original diamond drillholes net but closer spaced. This procedure is not the best in mathematical sense for selecting a location. The impact of an additional information to reduce the uncertainty about the parameter been modeled is not the same everywhere within the deposit. Some locations are more sensitive in reducing the local and global uncertainty than others. This study introduces a methodology to select additional sample locations based on stochastic simulation. The procedure takes into account data variability and their spatial location. Multiple equally probable models representing a geological attribute are generated via geostatistical simulation. These models share basically the same histogram and the same variogram obtained from the original data set. At each block belonging to the model a value is obtained from the n simulations and their combination allows one to access local variability. Variability is measured using an uncertainty index proposed. This index was used to map zones of high variability. A value extracted from a given simulation is added to the original data set from a zone identified as erratic in the previous maps. The process of adding samples and simulation is repeated and the benefit of the additional sample is evaluated. The benefit in terms of uncertainty reduction is measure locally and globally. The procedure showed to be robust and theoretically sound, mapping zones where the additional information is most beneficial. A case study in a coal mine using coal seam thickness illustrates the method. 相似文献
10.
复杂地形任意天气情形下太阳直接辐射量模拟 总被引：2，自引：1，他引：1
以太阳辐射传输参数化模型为基础,结合MODIS影像两次白天的云产品和水汽产品及DEM,构建了复杂地形任意天气情形下每日太阳直接辐射量模型。选取代表不同气候类型与地形起伏状况的3个典型站点（拉萨、北京、额济纳旗）,以2007年每日实测值对模拟结果进行了验证,其相关系数分别为0.77、0.77和0.85。研究表明:有云天气下,云是影响地表太阳直接辐射数量和空间分布的主要因子;模型对时间步长不敏感。引起误差的原因主要是MODIS云产品的时空分辨率较低以及云的3D效应导致模拟的困难,对地形起伏较大地区,小比例尺的DEM也会导致较大的误差,同时实测值与模拟值的空间尺度不匹配也引起了一定误差。 相似文献
11.
利用西北干旱半干旱区一次飞机探测资料、卫星资料,分析了层状云微物理结构以及作业前后云微物理变化,结果表明：（1） 此次层状云系垂直结构配置为冷暖两层,云层发展厚实。云的垂直和水平分布极不均匀。相对层积云,高层云小云粒子浓度低,大云粒子浓度高,液态含水量高。小云粒子浓度尤其是峰值区域与平均直径呈明显反相关。大于60个·cm-3和35个·L-1的小云、大云粒子浓度分别主要由3.5~10 μm、50~200 μm粒径段决定。（2） 不同高度云粒子谱为单峰或双峰分布,总体呈单调递减趋势,但云形成和增长条件存在差异。强可播、不可播和可播性冷云粒子谱基本符合负幂指数的单调递减规律,云粒子浓度差异较大,自然冰晶浓度不可播云较高,可播云次之,强可播云较低。（3） 作业后小云粒子浓度明显降低,在6.5~20 μm粒径段降低了2个量级左右,大云粒子浓度明显增加,谱宽增大,尤其在大于150 μm粒径段。 相似文献
12.
The Senegal River Basin (SRB) is a shared watershed in West Africa which includes regions (the upper basin, valley, and delta),
characterized by distinct environmental conditions. An important feature of the Senegal River flow volume historically was its inter-
annual irregularity, which caused a major water resource constrain. This situation has been accentuated during the long-term
drought (1969–1984) in the Sahel zone which highlights the vulnerability of food-producing systems to climate change and variability.
SRB is undergoing fundamental environmental, hydrologic, and socioeconomic transitions and represents a good illustration of sensitivity
to climatic variations and opportunities for adaptation. This paper aims to study water resources systems under stress from climate
variability and change in the Senegal River Basin. The results show (1) through the compilation of available data, information
and knowledge (sedimentological, climatical, geological, environmental, archeological, etc.), the chronological consequences of climate
change during the past millennium in West Africa, and also (2) an analysis of the recent impacts and vulnerability to climate
change in the SRB and finally (3) the adaptation strategies in the SRB in order to identify and resolve problems associated with
this water scarcity and to address the potential for guaranteed agricultural production in this narrow geographic area. 相似文献
13.
棉花叶面积指数（LAI）是描述其长势的重要指标,准确获取冠层结构参数是叶面积指数反演的必要条件。以ScoutB-100油动单旋翼无人机为飞行平台,搭载RIEGL VUX-1激光雷达,精确获取棉花高密度点云数据,得到研究区棉田数字表面模型（DSM）和数字高程模型（DEM）,通过差值运算获得其冠层高度模型（CHM）,进而提取有效的冠层结构参数。利用相关性分析法选取相关系数大于0.2的激光穿透力指数（LPI）、回波点云密度（D）、孔隙率（fgap）、归一化高程值（VnDSM）构建棉花LAI反演模型,并与实测叶面积指数进行精度验证与评价。实验结果表明：模型估算的LAI与实测LAI之间的决定系数为0.824,均方根误差为0.072,验证了模型的可靠性。 相似文献
14.
Yee Leung Tung Fung Ju‐Sheng Mi Wei‐Zhi Wu 《International journal of geographical information science》2013,27(9):1033-1058
This paper proposes a novel rough set approach to discover classification rules in real‐valued spatial data in general and remotely sensed data in particular. A knowledge induction process is formulated to select optimal decision rules with a minimal set of features necessary and sufficient for a remote sensing classification task. The approach first converts a real‐valued or integer‐valued decision system into an interval‐valued information system. A knowledge induction procedure is then formulated to discover all classification rules hidden in the information system. Two real‐life applications are made to verify and substantiate the conceptual arguments. It demonstrates that the proposed approach can effectively discover in remotely sensed data the optimal spectral bands and optimal rule set for a classification task. It is also capable of unraveling critical spectral band(s) discerning certain classes. The framework paves the road for data mining in mixed spatial databases consisting of qualitative and quantitative data. 相似文献
15.
Summary. A modification of the Aid et al . technique for three-dimensional lithospheric modelling is used to find smoothly varying models for the P -wave velocity structure beneath NORSAR. The method includes ray tracing and calculation of geometrical spreading in the anomalies. The results of linear inversion of the travel-time data compare well with those of previous investigators. The assumption of linearity, which removes the need to ray trace through the anomalies, is tested with iterative solutions for both synthetic and real data. A model with an rms velocity perturbation of 3 per cent, extending to 120 km depth, is found to be reasonably linear. In fact the procedure leads to two models which satisfy the same amount of the real data but which differ by far more than the standard errors. However, these differences are not significant once the imperfect resolution is accounted for by using the total estimation error of the stochastic inverse.
The depth of major anomalies appears to be greater than the array diameter and is therefore not well constrained. Comparing the geometrical spreading produced by these models with the amplitude variations observed at the array indicates that structure deeper than 120 km but shallower than 200 km makes an important contribution to the observations. None of the models used can produce variations as large as those in the amplitude data. For deep, essentially two-dimensional, anomalies the fit to these data is much better for sources to the NE of the array than for sources in other quadrants. 相似文献
The depth of major anomalies appears to be greater than the array diameter and is therefore not well constrained. Comparing the geometrical spreading produced by these models with the amplitude variations observed at the array indicates that structure deeper than 120 km but shallower than 200 km makes an important contribution to the observations. None of the models used can produce variations as large as those in the amplitude data. For deep, essentially two-dimensional, anomalies the fit to these data is much better for sources to the NE of the array than for sources in other quadrants. 相似文献
16.
Michele Crosetto Stefano Tarantola 《International journal of geographical information science》2013,27(5):415-437
A novel procedure to analyse the uncertainty associated to the output of GIS-based models is presented. The procedure can handle models of any degree of complexity that accept any kind of input data. Two important aspects of spatial modelling are addressed: the propagation of uncertainty from model inputs and model parameters up to the model output (uncertainty analysis); and the assessment of the relative importance of the sources of uncertainty in the output uncertainty (sensitivity analysis). Two main applications are proposed. The procedure allows implementation of a GIS-based model whose output can reliably support the decision process with an optimized allocation of resources for spatial data acquisition. This is possible in low cost strategy, based on numerical simulations on a small prototype of the GIS-based model. Furthermore, the procedure provides an effective model building tool to choose, from a group of alternative models, the best one in terms of cost-benefit analysis. A comprehensive case study is described. It concerns the implementation of a new GIS-based hydrologic model, whose goal is providing near real-time flood forecasting. 相似文献
17.
根据Aqua MODIS 2级云产品和Cloudsat的2级产品资料,结合降水数据和MODIS L1B级辐射率数据,对发生在京津冀地区夏季的三次强降水过程中冰云的宏微观物理量的特征进行分析,并探究这些物理量和降水强度的关系。结果表明：在水平分布中,强降水过程中降水强度高值区内云相为冰云,冰云云顶高度在8~17 km,冰云粒子有效半径、冰云光学厚度、冰水路径分别最高可达60 μm、 150、 5 000 g?m-2;冰云光学厚度、冰水路径、冰云云顶高度随降水强度增大而增大。在垂直分布中,冰云主要分布在3.5 km以上,发生强降水站点的冰云为深对流云,冰云粒子有效半径、冰水含量、冰云粒子数浓度分别最高可达150 μm、 3 000 mg?m-3 、 500 L-1;冰云粒子有效半径高值区存在于云层中下部,且随高度上升而减小,冰云粒子数浓度高值区存在于云层中上部,且随高度上升而增加,冰水含量高值区则存在于云层中部;冰云粒子有效半径、冰水含量、冰云粒子数浓度在9 km以上随降水强度增大而增大。 相似文献
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1960~2005年西北地区低云量的时空变化及成因分析 总被引：4，自引：0，他引：4
基于西北地区177个站点1960~2005年逐日的低云量观测资料,运用地统计学、交叉小波分析和多元回归分析,分析了近46 a来西北地区低云量的时空变化特征及影响因素。结果表明：近46 a来西北地区低云量呈较显著上升趋势,1997年之后上升显著。低云量空间呈自东南向西北递减的趋势。低云量与降水、相对湿度等呈显著的正相关,与昼夜温差、日照时数等呈显著的负相关。低云量存在2~4 a、准6 a、准11 a的周期变化,与宇宙射线在1982~1993年存在5~8 a的共振周期,与NOI指数存在2~4 a、准5 a、准11 a的共振周期,和太阳黑子的共振周期为9~11 a。 相似文献
20.
贵州和四川盆地云量的气候研究 总被引：1，自引：1，他引：0
贵州和四川盆地是我国云量最多的地区,素有“天无三日晴”和“蜀犬吠日”之说,盆地西缘的雅安古时还有“雅州天漏”的谚语。从全球日照百分率分布推知,川黔地区也是世界上天气最阴沉的地区之一。川黔之阴一向为国内外气象界所注意,本文根据1951—1980 相似文献