基于边缘检测算法的LiDAR数据建筑物提取     

CUI Jian-Jun  SUI Li-chun  XU Hua-zhi  ZHAO Dan 《测绘学院学报》2008,(2)

LiDAR技术可以快速获取地形表面高精度3维信息。基于LiDAR数据提取建筑物目标是这一技术的重要应用之一。探讨了一种基于LiDAR点云数据生成不同比例尺的DSM深度影像,然后利用边缘检测算子提取建筑物边缘的方法。实验证明,该方法不需要其他辅助数据,可以从LiDAR点云数据中提取建筑物边缘,并滤除了许多干扰信息。这种方法为基于LiDAR数据提取建筑物目标提供了新的思路。  相似文献   

基于小波变换的CBERS-02图像薄云薄雾去除的方法研究     

郭向前 《测绘科学》2008,(Z1)

大气活动的干扰是遥感技术发展的最大限制之一,对星载的可见光、近红外波段的光学探测器而言,大气中云雾的干扰更是不易处理。为了促进CBERS-02星CCD传感器图像的定量化应用,在对以往有关遥感图像薄云去处方法的研究的基础上,本文提出了对含薄云的CBERS-02 CCD图像进行适当层次的小波分解,然后对分解的图像进行同态滤波,最后进行图像重构而去除薄云的方法。试验结果表明,该方法既能有效的去除薄云,又可较好的保持图像细节。  相似文献   

Precipitation interception in Australian tropical rainforests: II. Altitudinal gradients of cloud interception,stemflow, throughfall and interception     

David McJannet  Jim Wallace  Paul Reddell 《水文研究》2007,21(13):1703-1718

This article presents a comprehensive study of canopy interception in six rainforests in Australia's Wet Tropics for periods ranging between 2 and 3·5 years. Measurements of rainfall, throughfall, stemflow and cloud interception were made at sites characterized by different forest types, canopy structure, altitude, rainfall and exposure to prevailing winds. Throughfall at these sites ranged between 64 and 83% of total precipitation inputs, while stemflow ranged between 2 and 11%. At sites higher than 1000 m, cloud interception was found to contribute up to 66% of the monthly water input to the forest, more than twice the rainfall at these times. Over the entire study period, cloud interception accounted for between 4 and 30% of total precipitation inputs, and was related more to the exposure of sites to prevailing winds than to altitudinal differences alone. Over the duration of the study period, interception losses ranged between 22 and 29% of total water input (rainfall and cloud interception) at all sites except the highest altitude site on Bellenden Ker, where interception was 6% of total water input. This smaller interception loss was the result of extremely high rainfall, prolonged immersion in cloud and a sparser canopy. On a monthly basis, interception losses from the six sites varied between 10 and 88% of rainfall. All sites had much higher interception losses during the dry season than in the wet season because of the differences in storm size and rainfall intensity. The link between rainfall conditions and interception losses has important implications for how evaporative losses from forests may respond to altered rainfall regimes under climate change and/or large‐scale atmospheric circulation variations such as El Niño. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Interplanetary Transients and Cosmic-Ray Anisotropy     

Rajesh K. Mishra  Rekha Agarwal Mishra 《Solar physics》2007,240(2):359-372

Cosmic-ray intensity data recorded with the ground-based neutron monitor at Deep River have been investigated taking into account the associated interplanetary magnetic field and solar-wind plasma data during 1981 – 1994. A large number of days having abnormally high or low amplitudes for five or more successive days as compared to the annual average amplitude of diurnal anisotropy have been taken as high- or low-amplitude anisotropic wave-train events. The amplitude of the diurnal anisotropy of these events is found to increase on days with a magnetic cloud as compared to the days prior to the event, and it is found to decrease during the later period of the event as the cloud passes the Earth. The high-speed solar-wind streams do not play any significant role in causing these types of events. However, corotating solar-wind streams produce significant deviations in cosmic-ray intensity during high- and low-amplitude events. The interplanetary disturbances (magnetic clouds) are also effective in producing cosmic-ray decreases. Hα solar flares have a good positive correlation with both the amplitude and direction of the anisotropy for high-amplitude events, while the principal magnetic storms have a good positive correlation with both amplitude and direction of the anisotropy for low-amplitude events. The source responsible for these unusual anisotropic wave trains in cosmic rays has been proposed.  相似文献   

基于MPI环境的并行程序设计     

张建文  徐琼  王强 《华东地质学院学报》2007,30(1):81-84

MPI(Message Passing Interface)是消息传递并行程序设计的标准之一,概述了MPI的概念和组成,着重介绍了支持并行程序设计的消息传递接口(MPI)以及在MPI环境下的并行程序设计方法,并给出一个MPI并行程序设计实例,说明了MPI的程序设计流程和主从并行计算流程,由此提出了一个Master/Slave结构的设计模式。  相似文献   

Sensitivity of surface radiation budget to clouds over the Asian monsoon region   总被引：1，自引：0，他引：1  

S Balachandran  M Rajeevan 《Journal of Earth System Science》2007,116(2):159-169

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构建GIS高可信服务计算环境探讨     

吴信才  陈占龙  吴亮 《地理与地理信息科学》2007,23(4):5-8

基于面向服务的分布式空间信息支撑平台,从高可信网络计算环境、高可信空间信息、高可信软件、高可信计算平台4方面探讨构建GIS高可信服务计算环境的方法及其关键技术。为实现GIS空间信息存储的可靠性和发布的安全性,建立了基于角色访问控制权限的空间数据管理模型,并研究空间信息发布的中间件技术,展望构建GIS高可信服务计算环境的发展趋势和突破点。  相似文献   

粒度Hough变换及其在遥感影像直线检测中的应用   总被引：1，自引：0，他引：1  

巫兆聪  万茜婷  梁静  周正 《武汉大学学报(信息科学版)》2007,32(10):860-863

在基于Hough变换的遥感影像直线检测的过程中引入粒度计算的概念,利用粒度计算具有多角度、多层次观察问题的能力,对遥感影像中的直线边缘特征进行不同粗细的粒度分析,建立粒度计算概念下的直线检测算法,实现对不同长短、粗细直线的识别。真实的IKONOS遥感影像机场跑道提取试验证明了该方法的有效性。  相似文献   

Microphysical Effects of Cloud Seeding in Supercooled Stratiform Clouds Observed from NOAA Satellite     

DAI Jin  YU Xin  Daniel ROSENFELD  XU Xiaohong 《Acta Meteorologica Sinica》2007,21(2):224-233

Based on the satellite retrieval methodology, the spectral characteristics and cloud microphysical properties were analyzed that included brightness temperatures of Channels 4 and 5, and their brightness temperature difference (BTD), the particle effective radius of seeded cloud track caused by an operational cloud seeding and the microphysical effects of cloud seeding were revealed by the comparisons of their differences inside and outside the seeded track. The cloud track was actually a cloud channel reaching 1.5-km deep and 14-km wide lasting for more than 80 min. The effective radius of ambient clouds was 10-15μm, while that within the cloud track ranged from 15 to 26μm. The ambient clouds were composed of supercooled droplets, and the composition of the cloud within the seeding track was ice. With respect to the rather stable reflectance of two ambient sides around the track, the visible spectral reflectance in the cloud track varied at least 10%, and reached a maximum of 35%, the reflectance of 3.7μm in the seeded track relatively decreased at least 10%. As cloud seeding advanced, the width and depth were gradually increased. Simultaneously the cloud top temperature within the track became progressively warmer with respect to the ambient clouds, and the maximum temperature differences reached 4.2 and 3.9℃at the first seeding position for Channels 4 and 5. In addition, the BTD in the track also increased steadily to a maximum of 1.4℃, compared with 0.2-0.4℃of the ambient clouds. The evidence that the seeded cloud became thinner comes from the visible image showing a channel, the warming of the cloud tops, and the increase of BTD in the seeded track. The seeded cloud became thinner mainly because the cloud top descended and it lost water to precipitation throughout its depth. For this cloud seeding case, the glaciation became apparent at cloud tops about 22 min after seeding. The formation of a cloud track in the supercooled stratiform clouds was mainly because that the seeded cloud volume glaciated into ice hydrometeors that precipitated and so lowered cloud top height. A thin line of new water clouds formed in the middle of the seeded track between 38 and 63 min after seeding, probably as a result of rising motion induced by the released latent heat of freezing. These clouds disappeared in the earlier segments of the seeded track, which suggested that the maturation of the seeding track was associated with its narrowing and eventual dissipation due to expansion of the tops of the ambient clouds from the sides inward.  相似文献   

Heterogeneities in the Microstructure and Composition of Aircraft Engine Combustor Soot: Impact on the Water Uptake     

B. Demirdjian  D. Ferry  J. Suzanne  O. B. Popovicheva  N. M. Persiantseva  N. K. Shonija 《Journal of Atmospheric Chemistry》2007,56(1):83-103

Size, morphology, microstructure, chemical composition and hygroscopic properties of aircraft engine combustor (AEC) soot particles are studied by using a combination of several methods, namely atomic force microscopy, transmission electron microscopy, gravimetry, ionic chromatography analysis and wetting observations. From the microstructure and the composition of soot agglomerates, we find that we can separate AEC soot in two fractions having quite different physico-chemical properties: a main fraction of particles containing essentially amorphous carbon with small amounts of oxygen, sulfur and iron and a fraction of impurities characterized by various structures and a large amount of impurities. These properties of aircraft engine combustor soot are compared to those of soot obtained by burning TC1 aviation kerosene in a laboratory burner. It is shown that TC1 soot can be a good surrogate of the AEC main fraction. Such a finding allows us to perform water uptake measurements and to conclude that the AEC main fraction is rather hydrophobic whereas the AEC fraction of impurities is highly hydrophilic The ability of the two fractions of aircraft engine combustor soot to act as cloud condensation nuclei is discussed with respect to their implication in contrail and cirrus formation.Associated to Université de la Méditerranée (Aix-Marseille II) and to Université Paul Cézanne (Aix-Marseille III)  相似文献