The topographic normalization of hyperspectral data: implications for the selection of spectral end members and lithologic mapping

Compact Airborne Spectrographic Imager (CASI) hyperspectral data is used to investigate the effects of topography on the selection of spectral end members, and to assess whether the topographic correction improves the discrimination of rock units for lithologic mapping. A publicly available Digital Elevation Model (DEM), at a scale of 1:50,000, is used to model the radiance variation of the scene as a function of topography, assuming a Lambertian surface. Skylight is estimated and removed from the airborne data using a dark object correction. The CASI data is corrected on a pixel-by-pixel basis to normalize the scene to a uniform solar illumination and viewing geometry. The results show that topography has the effect of expanding end member clusters at times resulting in the overlap of clusters and that the correction process can effectively reduce the variation in detected radiance due to changes in local illumination. When topographic effects are embedded in the hyperspectral data, methods typically used for the selection of end members, such as the convex hull method, can miss end members or result in the selection of nonrepresentative pixels as end members. Thus, end members selected by some conventional methods are very likely “incomplete” or “nonrepresentative” if the topographic effect is embedded in the data. As shown in this study, the topographic correction can reveal hidden end members and achieve a better representation of end members via the statistical center of isolated clusters.     

工业配料中的自控

本文介绍了微机在工业配料过程中的应用情况，对上料-计量-下料的全过程即“动态运行-静态计量-动态运行”进行控制．     

A data porting tool for coupling models with different discretization needs

The presented work is part of a larger research program dealing with developing tools for coupling biogeochemical models in contaminated landscapes. The specific objective of this article is to provide researchers with a data porting tool to build hexagonal raster using information from a rectangular raster data (e.g. GIS format). This tool involves a computational algorithm and an open source software (written in C). The method of extending the reticulated functions defined on 2D networks is an essential key of this algorithm and can also be used for other purposes than data porting. The algorithm allows one to build the hexagonal raster with a cell size independent from the geometry of the rectangular raster. The extended function is a bi-cubic spline which can exactly reconstruct polynomials up to degree three in each variable. We validate the method by analyzing errors in some theoretical case studies followed by other studies with real terrain elevation data. We also introduce and briefly present an iterative water routing method and use it for validation on a case with concrete terrain data.     

基于GIS的乌江流域新安江模型参数率定

为了使新安江模型的运用更能真实反映流域的基本特征及产汇流机理,利用地理信息系统空间分析的功能,由数字高程模型导出乌江武隆以上流域的流域排水网,并在此基础上提取汇流长度及坡度等地形特征值。在地理信息系统平台上,计算出流域下垫面的植被、土壤、地貌等特征值,并将其与流域模型参数建立相关关系。结果表明,各流域模拟的确定性系数及模拟精度均较高。因此,预报结果更加合理,理论依据也更加可靠。     

不同算法下生成的数字高程模型对比分析研究

目前数字高程模型的生成在大多数商用地理信息系统软件或遥感图像处理软件中都能实现,但提供的算法有所不同.结合目前常用专业软件提供的不同算法,对同一数据源的高程数据分别生成数字高程模型(DEM),进行对比分析后发现:使用现有专业软件生成的DEM均存在着差异,这些差异主要来源于不同软件采用的算法差别,并且DEM的差异具有空间分布的规律性和负高差多于正高差的特点.由此得出以下结论,TIN算法具有生成的DEM精度高等优点,LRS和Non-LRS算法具有生成的DEM结构简单等优点.若要进行三维显示、土方量计算等,则选择TIN算法生成;若要检查高程数据错误,则选择LRS或Non-LRS算法生成.     

Recent elevation changes of Svalbard glaciers derived from ICESat laser altimetry

We have tested three methods for estimating 2003-2008 elevation changes of Svalbard glaciers from multi-temporal ICESat laser altimetry: (a) linear interpolation of crossover points between ascending and descending tracks, (b) projection of near repeat-tracks onto common locations using Digital Elevation Models (DEMs), and (c) least-squares fitting of rigid planes to segments of repeat-track data assuming a constant elevation change rate. The two repeat-track methods yield similar results and compare well to the more accurate, but sparsely sampled, crossover points. Most glacier regions in Svalbard have experienced low-elevation thinning combined with high-elevation balance or thickening during 2003-2008. The geodetic mass balance (excluding calving front retreat or advance) of Svalbard's 34,600 km² glaciers is estimated to be −4.3 ± 1.4 Gt y⁻¹, corresponding to an area-averaged water equivalent (w.e.) balance of −0.12 ± 0.04 m w.e. y⁻¹. The largest ice losses have occurred in the west and south, while northeastern Spitsbergen and the Austfonna ice cap have gained mass. Winter and summer elevation changes derived from the same methods indicate that the spatial gradient in mass balance is mainly due to a larger summer season thinning in the west and the south than in the northeast. Our findings are consistent with in-situ mass balance measurements from the same period, confirming that repeat-track satellite altimetry can be a valuable tool for monitoring short term elevation changes of Arctic glaciers.     

Near-global validation of the SRTM DEM using satellite radar altimetry

This paper reports the results of a near-global validation of the SRTM DEM dataset, using a unique database of completely independent height measurements derived from satellite altimeter echoes, primarily gathered by ERS-1. These heights are obtained using a rule-based expert system which identifies each echo as 1 of 11 different characteristic shapes, and selects the optimal retracking algorithm to obtain best range to surface. The results of this comparison, which includes over 54 million altimeter derived heights, show generally very good agreement with the SRTM data, with global statistics for mean difference of 3 m and a standard deviation of 16 m. Quantitative validation results are given for each continent and are summarised here.

	Mean difference (m)	Standard deviation of differences (m)
Africa	1.86	15.62
Australia	1.09	11.49
Eurasia	2.54	16.09
North America	3.15	15.18
South America	12.22	18.51
Global	3.60	16.16

Full-size table

     

虚拟地形建模及运动目标实时监测的研究

随着虚拟现实技术、3S技术、网络技术的发展,地形三维可视化和目标监测等方面已成为研究的热点。该文结合开发的应用系统论述了实现地球三维可视化的建模方法,以及Internet环境下在三维虚拟地形上实现目标监测的技术。     

高程点与高程注记的匹配及其应用

在基于AutoCAD的地形图中,提出解决高程点与高程注记匹配方法,并利用高程注记作为高程点的属性的方法实现高程点与高程注记的组合,以及在高程处理中的一些应用.     

一种高精度DEM的制作方法探讨

DEM是表示地面高程的一种实体地面模型,是三维数字城市建设必不可少的基础数据,其生产方法有很多种,本文以青岛市1∶5 000航测项目（C标段）为例,利用航测工作站VirtuoZo 3.7软件,通过引入特征地物与添加辅助线相结合的方式,介绍了一种快速制作高精度DEM的方法。