合肥市紫外线指数预报业务系统的分析和研究

介绍了合肥地区紫外线预报系统的建立依据以及功能。由于紫外线和太阳高度角、云量等要素之间有很好的相关性,利用2004~2006年紫外线观测资料和同期气象资料,运用统计学方法建立紫外线预报方程,并根据预报方程建立一个集资料采集、信息查询、预报制作、产品发布、定量评分于一体的具有较好的人机交互的紫外线预报业务系统。     

基于ArcGIS环境下DEM流域特征提取及应用

该文详细介绍了ArcGIS9.2中的水文分析工具箱的使用方法,包括从原始DEM数据提取河网的步骤、应注意的问题等。研究区域选取位于北京山区的红门川小流域,采用1∶10000的比例尺、10m分辨率的DEM作为基本的地形数据,应用ESRI公司开发的ArcGIS9.2地理信息系统软件进行流域水文信息特征的提取;并利用SWAT模型运行水文响应单元(HRUs)的生成,共生成了25个子流域和92个HRUs。经分析,得到的研究区域河网特征以及研究区其他常用的流域特征信息,与实际河流水系特征基本吻合,因此应用DEM划分的流域结果是合理的。     

Site selection for a measuring and controlling device of initial phase based on maximum elevation angle

We introduced a site selection method based on the modified maximum elevation angle intended for mountains possibly affecting the measurement and control of the initial phase in a launching port located in mountainous areas. To use the former analysis results, the method, along the helices whose center is the launcher's project point, analyze each point's visibility on the helices. The visible area can be obtained by comparing the visibility at each moment in the initial phase. Finally, there can be three points in the above visible area with distances longer than required.     

邓恩桉在福建南平不同海拔区的生长调查

对延平区三乡镇邓恩桉遭遇两次历史低温后生长情况进行调查分析,结果表明不同海拔高度对邓恩桉生长影响显著。邓恩桉新造林对持续的低温很敏感,成林后其耐寒能力大大增强,但海拔较高的地区种植邓恩桉其蓄积量小于当地杉木、马尾松的蓄积量,这与邓恩桉本身的生物学特性有关。邓恩桉在海拔≤260m、土层厚≥80cm的Ⅰ、Ⅱ类缓坡地生长状态好,4a生邓恩桉平均蓄积量达31.8m3·hm-2。     

Final Analysis of the Accuracy and Precision of Methods to Calculate the Sediment Retained by Check Dams

Knowing how much sediment check dams have trapped during their lifespan is essential to estimate their effectiveness or the sediment yields of their basins. Methods to calculate the volume of sediment trapped by check dams play an important role in the understanding of these issues. Several authors have proposed different methods to measure the volume of retained sediment, but their accuracy has, as yet, not been precisely determined and is currently a subject of debate. We compare the most frequently used methods (geometric: prism, pyramid and geometric; topographic: Digital Terrain Models (DTMs), trapezoids and sections methods) to evaluate their accuracy and precision in determining the volume of sediment retained by check dams. Our calculations are based on ten virtual check dams simulated in several gullies of Saldaña (Spain), where we determine their volumetric capacity for trapping sediment (real volume). This was made by means of an intensive topographic survey of these gullies, employing a terrestrial laser scanning system to obtain a high‐resolution digital elevation model (5 × 5 cm, ±2 mm). The results showed that topographic methods provided a very good fit to real volume with a difference of around 8%, being the sections method the most accurate. Geometric methods were less accurate, showing differences of up to 28%. Thus, the results obtained until now by geometric methods should be considered with caution. Although topographic methods were more accurate, they require many field data and much time than the others. So geometric methods can still be useful by correcting their results using our obtained percentage of variation. Knowing the accuracy of the methods before measuring is essential to obtain the most reliable results to analyse the role of check dams in controlling sediment, erosion processes and land degradation. Copyright © 2017 John Wiley & Sons, Ltd.     

Deriving river networks and catchments at the European scale from medium resolution digital elevation data

The extraction of drainage networks and catchment boundaries from digital elevation models (DEMs) has received considerable attention in recent years and is recognized as a viable alternative to traditional surveys and the manual evaluation of topographic maps. However, most studies have covered limited areas due to the lack of detailed information and/or the lack of highly efficient algorithms. In this paper we present an application that delineates river networks and catchment boundaries across the European continent from a medium resolution (250 m) DEM. We exploit novel algorithms based on the concepts of mathematical morphology and implement a landscape stratification for drainage density.A flow direction grid is computed using an efficient algorithm for the removal of spurious pits. River networks are then derived by imposing a variable threshold for the minimum contributing area needed to form and maintain a channel. This is achieved through a landscape stratification that reflects the ability of the terrain to develop different drainage densities. It is shown that the analysis of environmental characteristics coupled with the analysis of local slope versus contributing area enables river network mapping with a spatially varying drainage density. The result has been validated by comparing the derived data to digital river and catchment data from other sources and with varying scales of observation.     

不同比例尺数字高程模型对土壤侵蚀强度分级的影响

基于1∶5万和1∶50万2种不同比例尺的数字高程模型(DEM),结合土地利用类型、植被覆盖度等指标,对试验区土壤侵蚀强度进行了分级,并对不同比例尺DEM求算的坡度差异及其对土壤侵蚀强度分级的影响进行了分析。结果表明:1∶50万DEM较1∶5万DEM综合了大量信息,求算的坡度整体上偏小而使分级结果多集中在微度侵蚀区;不同地貌单元受DEM信息综合的影响不同,地形平坦的山前岗地区受影响最大,而地形复杂的中山区受影响相对较小。     

数字高程模型和多时相MODIS数据复合的水稻种植面积遥感估算方法研究

随着搭载在TERRA卫星上的中分辨率成像光谱仪(MODIS)的出现,它以数据丰富、时间分辨率高和覆盖范围广等特点，为水稻遥感估产提供了较好的数据源。该文利用水稻种植易受坡度影响的特性，从数字高程模型(Digital Elevation Models简称DEM)中提取坡度信息，考虑到MODIS能提供多时相及丰富的数据，采用DEM产生的坡度和两个时相MODIS影像数据及植被指数复合提取水稻种植面积，经过比较试验证明，在南方丘陵山区的复杂地形区域,多源信息复合相对于单纯利用单景影像数据可以明显提高水稻种植面积估算的精度。     

Cotton lint yield variability in a heterogeneous soil at a landscape scale

Landscape variability associated with topographic features affects the spatial pattern of soil water and N redistribution, and thus N uptake and crop yield. A landscape-scale study was conducted in a center pivot irrigated field on the southern High Plains of Texas in 1999 to assess soil water, soil NO₃-N, cotton (Gossypium hirsutum L.) lint yield, and N uptake variability in the landscape, and to determine the spatial correlation between these landscape variables using a state-space approach. The treatments were irrigation at 50 and 75% cotton potential evapotranspiration (ET). Neutron access tubes were placed at a 15-m interval along a 710 m (50% ET) and 820 m (75% ET) transect across the field. Soil NO₃-N in early spring was autocorrelated at a distance varying between 60 and 80 m. Measured soil volumetric water content (WC), total N uptake, and lint yield were generally higher on lower landscape positions. Cotton lint yield was significantly correlated to soil WC (r=0.76), soil NO₃-N (r=0.35), and site elevation (r=−0.54). Differences of site elevation between local neighboring points explained the soil water, NO₃-N and lint yield variability at the micro-scale level in the landscape. Soil WC, cotton lint yield, N uptake, and clay content were crosscorrelated with site elevation across a lag distance of ±30–40 m. The state-space analysis showed that cotton lint yield was positively weighted on soil WC availability and negatively weighted on site elevation. Cotton lint yield state-space models give insights on the association of soil physical and chemical properties, lint yield, and landscape processes, and have the potential to improve water and N management at the landscape-scale.