排序方式： 共有158条查询结果，搜索用时 15 毫秒
51.
The new MOdèle de Chimie Atmosphérique à Grande Echelle (MOCAGE) three-dimensional multiscale chemistry and transport model (CTM) has been applied to study heavy pollution episodes observed during the ESCOMPTE experiment. The model considers the troposphere and lower stratosphere, and allows the possibility of zooming from the planetary scale down to the regional scale over limited area subdomains. Like this, it generates its own time-dependent chemical boundary conditions in the vertical and in the horizontal. This paper focuses on the evaluation and quantification of uncertainties related to chemical and transport modelling during two intensive observing periods, IOP2 and IOP4 (June 20–26 and July 10–14, 2001, respectively). Simulations are compared to the database of four-dimensional observations, which includes ground-based sites and aircraft measurements, radiosoundings, and quasi-continuous measurements of ozone by LIDARs. Thereby, the observed and modelled day-to-day variabilities in air composition both at the surface and in the vertical have been assessed. Then, three sensitivity studies are conducted concerning boundary conditions, accuracy of the emission dataset, and representation of chemistry. Firstly, to go further in the analysis of chemical boundary conditions, results from the standard grid nesting set-up and altered configurations, relying on climatologies, are compared. Along with other recent studies, this work advocates the systematic coupling of limited-area models with global CTMs, even for regional air quality studies or forecasts. Next, we evaluate the benefits of using the detailed high-resolution emissions inventory of ESCOMPTE: improvements are noticeable both on ozone reactivity and on the concentrations of various species of the ozone photochemical cycle especially primary ones. Finally, we provide some insights on the comparison of two simulations differing only by the parameterisation of chemistry and using two state-of-the-art chemical schemes for regional photochemical modelling. Regional air quality modelling is found to be highly sensitive to the emission inventory dataset and also to the vertical and horizontal boundary conditions and detailed representation of chemistry. Interestingly enough, they infer the same range of errors compared to total model errors. 相似文献
52.
一些大型的工程项目在前期使用航飞LIDAR系统采集地面数据,获取了大量的三维点云数据和DOM影像数据,要制作该项目全区域的线划图,使用传统的制图方法,不仅效率低,而是几乎不可能完成该项工作。因为海量数据已经让传统的AutoCAD平台制图软件不堪重负,基于此原因,必须研究探索新的方法,就是使用GIS方法来生产线划图。 相似文献
53.
This paper describes the preliminary development of a network‐index approach to modify and to extend the classic TOPMODEL. Application of the basic Beven and Kirkby form of TOPMODEL to high‐resolution (2·0 m) laser altimetric data (based upon the UK Environment Agency's light detection and ranging (LIDAR) system) to a 13·8 km2 catchment in an upland environment identified many saturated areas that remained unconnected from the drainage network even during an extreme flood event. This is shown to be a particular problem with using high‐resolution topographic data, especially over large appreciable areas. To deal with the hydrological consequences of disconnected areas, we present a simple network index modification in which saturated areas are only considered to contribute when the topographic index indicates continuous saturation through the length of a flow path to the point where the path becomes a stream. This is combined with an enhanced method for dealing with the problem of pits and hollows, which is shown to become more acute with higher resolution topographic data. The paper concludes by noting the implications of the research as presented for both methodological and substantive research that is currently under way. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
54.
Objective landslide detection and surface morphology mapping using high-resolution airborne laser altimetry 总被引：6，自引：0，他引：6
A map of extant slope failures is the most basic element of any landslide assessment. Without an accurate inventory of slope instability, it is not possible to analyze the controls on the spatial and temporal patterns of mass movement or the environmental, human, or geomorphic consequences of slides. Landslide inventory maps are tedious to compile, difficult to make in vegetated terrain using conventional techniques, and tend to be subjective. In addition, most landslide inventories simply outline landslide boundaries and do not offer information about landslide mechanics as manifested by internal deformation features. In an alternative approach, we constructed accurate, high-resolution DEMs from airborne laser altimetry (LIDAR) data to characterize a large landslide complex and surrounding terrain near Christchurch, New Zealand. One-dimensional, circular (2-D) and spherical (3-D) statistics are used to map the local topographic roughness in the DEMs over a spatial scale of 1.5 to 10 m. The bedrock landslide is rougher than adjacent unfailed terrain and any of the statistics can be employed to automatically detect and map the overall slide complex. Furthermore, statistics that include a measure of the local variability of aspect successfully delineate four kinematic units within the gently sloping lower half of the slide. Features with a minimum size of surface folds that have a wavelength of about 11 to 12 m and amplitude of about 1 m are readily mapped. Two adjacent earthflows within the landslide complex are distinguished by a contrast in median roughness, and texture and continuity of roughness elements. The less active of the earthflows has a surface morphology that presumably has been smoothed by surface processes. The Laplacian operator also accurately maps the kinematic units and the folds and longitudinal levees within and at the margins of the units. Finally, two-dimensional power spectra analyses are used to quantify how roughness varies with length scale. These results indicate that no dominant length scale of roughness exists for smooth, unfailed terrain. In contrast, zones with different styles of landslide deformation exhibit distinctive spectral peaks that correspond to the scale of deformation features, such as the compression folds. The topographic-based analyses described here may be used to objectively delineate landslide features, generate mechanical inferences about landslide behavior, and evaluate relatively the recent activity of slides. 相似文献
55.
56.
Automatic 3D extraction of building roofs from remotely sensed data is important for many applications including city modelling. This paper proposes a new method for automatic 3D roof extraction through an effective integration of LIDAR (Light Detection And Ranging) data and multispectral orthoimagery. Using the ground height from a DEM (Digital Elevation Model), the raw LIDAR points are separated into two groups. The first group contains the ground points that are exploited to constitute a ‘ground mask’. The second group contains the non-ground points which are segmented using an innovative image line guided segmentation technique to extract the roof planes. The image lines are extracted from the grey-scale version of the orthoimage and then classified into several classes such as ‘ground’, ‘tree’, ‘roof edge’ and ‘roof ridge’ using the ground mask and colour and texture information from the orthoimagery. During segmentation of the non-ground LIDAR points, the lines from the latter two classes are used as baselines to locate the nearby LIDAR points of the neighbouring planes. For each plane a robust seed region is thereby defined using the nearby non-ground LIDAR points of a baseline and this region is iteratively grown to extract the complete roof plane. Finally, a newly proposed rule-based procedure is applied to remove planes constructed on trees. Experimental results show that the proposed method can successfully remove vegetation and so offers high extraction rates. 相似文献
57.
Veena Joshi Devidas Tambe Gorakh Dhawade 《Journal of the Geological Society of India》2009,73(3):355-370
One of the most serious limitations in studying the surface morphometry of a badland landscape is the nonavailability of a
very fine resolution data which is essential for such types of studies. Local relief of most of the badlands in India and
also from other parts of the world exhibit limited relief amplitude, often within a few meters. The paper reports a case study
carried out in a riverine badland formed along the Western Deccan Trap Region. An attempt has been made in the present paper
to extract the morphometric variables of the landscape from the DEMs derived from a high resolution field generated data,
because the accuracy of the DEM derived values are dependent on the pixel resolution of the DEM from which they are generated.
The size of the pixel resolution should be fixed differently for different landscapes depending on the landscape process in
the area. The local relief of the area is around 10 m and for such types of landscapes the topographical maps and also the
web-available DEMs are of very coarse resolutions which are not suitable for the analysis. Therefore two well defined tributary
catchments were chosen from the area under investigation and theodolite surveys were carried out, contours were generated
with 10 cm interval, DEMs were derived by using Arc GIS software. SRTM (Shuttle Radar Topography Mission) 90 m resolution
data were utilized to generate DEM for the whole basin. Hypsometric and the drainage basin parameters were extracted from
these data by using the same software. Fractal dimension of the whole basin and the sample basins were also obtained for the
same data. The morphometric data generated were used to understand the geomorphic processes operating in the area. 相似文献
58.
基于等高线簇分析的复杂建筑物模型重建方法 总被引：1，自引：0，他引：1
近年来,基于LIDAR点云数据的建筑物重建模型一直是研究的热点。目前,出现的许多算法对简单建筑物,如平顶房屋、人字行屋顶及其他规则房屋的重建取得了不错的效果,但是,对于结构复杂的建筑物重建问题仍然有待解决。针对这一问题,本文提出了一种利用等高线簇分析从LIDAR数据中自动重建复杂建筑物模型的新算法。该算法是一种自底向上的数据驱动方法,以等高线所反映出的建筑物轮廓特征为基础,充分利用等高线封闭性和明确的拓扑关系,采用等高线形状分析的方法来实现建筑物的检测和模型识别与重建。算法实现分为4个步骤,首先,通过对LIDAR点云数据的DELAUNAY三角化跟踪提取等高线,然后利用等高线的长度,面积等形状参数来提取建筑物等高线,再通过拓扑分析,以及形状匹配的方法对等高线进行分簇,得到同一建筑物不同组成部分的等高线簇,最后,对各簇等高线进行模型参数优化并按拓扑关系进行重组得到完整的建筑物模型。通过对多层次、多曲面等复杂建筑物的重建实验证明了此方法的可行性。 相似文献
59.
Information on ecosystem services as a function of the successional stage for secondary tropical dry forests (TDFs) is scarce and limited. Secondary TDFs succession is defined as regrowth following a complete forest clearance for cattle growth or agriculture activities. In the context of large conservation initiatives, the identification of the extent, structure and composition of secondary TDFs can serve as key elements to estimate the effectiveness of such activities. As such, in this study we evaluate the use of a Hyperspectral MAPper (HyMap) dataset and a waveform LIDAR dataset for characterization of different levels of intra-secondary forests stages at the Santa Rosa National Park (SRNP) Environmental Monitoring Super Site located in Costa Rica. Specifically, a multi-task learning based machine learning classifier (MLC-MTL) is employed on the first shortwave infrared (SWIR1) of HyMap in order to identify the variability of aboveground biomass of secondary TDFs along a successional gradient. Our paper recognizes that the process of ecological succession is not deterministic but a combination of transitional forests types along a stochastic path that depends on ecological, edaphic, land use, and micro-meteorological conditions, and our results provide a new way to obtain the spatial distribution of three main types of TDFs successional stages. 相似文献
60.
A. A. Bidokhti M. Khoshsima S. Sabetghadam H. M. Khalesifard 《Journal of Earth System Science》2008,117(6):925-934
Air pollution predictions often require the height of atmospheric mixed layer in time especially in big cities. Here, the
variation of the height of this layer is estimated from direct measurements and also from a numerical forecast model with
a high resolution boundary layer scheme. The height of the daytime mixed layer for the city of Zanjan (48.5°N, 36.7°E, 1700m
above sea level) is measured using a LIDAR (532 nm) system, which works based on aerosols scattering of laser light. The mixed
layer height (z
i
) for Zanjan city, well above mean sea level compared to other major cities in the world, is found to be between 1.4 km typically
in spring and 2.2 km in summer, for synoptic calm conditions. Also, the MM5 forecast model with a proper boundary layer scheme
(MRF) is used to estimate z
i
which shows rather good agreement with direct observations using the LIDAR system. The entrainment zone of the mixed layer
was also found to undergo some occasional temporal growth that may be attributed to shear instability that led to more mixed
layer growth. 相似文献