Estimation of aboveground biomass and carbon in a tropical rain forest in Gabon using remote sensing and GPS data

The knowledge of biomass stocks in tropical forests is critical for climate change and ecosystem services studies. This research was conducted in a tropical rain forest located near the city of Libreville (the capital of Gabon), in the Akanda Peninsula. The forest cover was stratified in terms of mature, secondary and mangrove forests using Landsat-ETM data. A field inventory was conducted to measure the required basic forest parameters and estimate the aboveground biomass (AGB) and carbon over the different forest classes. The Shuttle Radar Topography Mission (SRTM) data were used in combination with ground-based GPS measurements to derive forest heights. Finally, the relationships between the estimated heights and AGB were established and validated. Highest biomass stocks were found in the mature stands (223 ± 37 MgC/ha), followed by the secondary forests (116 ± 17 MgC/ha) and finally the mangrove forests (36 ± 19 MgC/ha). Strong relationships were found between AGB and forest heights (R² > 0.85).     

中国流域的SRTM30数据提取与计算

本研究基于SRTM30数字高程模型数据,在运用D8算法计算流向的基础上,采用两种不同的方案分别提取中国的数字流域。一种是以中国国界为流出边界提取的详细的中国流域图,另外一种是将与中国接壤的周边地区包括在内提取出中国及邻近地区的流域分布图。结果表明,将与中国接壤的周边地区包含在提取范围内,得出的流域分布更能反映真实情况,对于国际间流域分布研究有着很重要的参考意义。而以中国国界提取出来的数字流域,虽然为国内相关研究广泛应用,但这种方法割裂了流域在地理上的天然联系。经过计算,采取第二种方法提取的中国范围内面积大于50 000km²的独立流域一共有23个,占总的流域面积的82.09%,与传统的中国流域划分不同的是,内陆河流域是中国第一大流域,由于处于干旱少雨的地区,该流域为人们所忽视,紧随其后的是长江、黄河、松花江、嫩江等主要流域。面积的估算理论误差在0.25%到1.73%之间。SRTM30数据质量高,1km的分辨率很适合像中国地区这样大范围的流域提取。并且可以采用更高分辨率的数据,继续进行水系的提取及其分级,从而提取出更精细的流域边界和水系分布。     

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三峡库区蓄水后地壳垂直变形场的模拟与分析

基于三峡库区DEM及现有GPS站点位置坐标数据,建立了三峡库区有限元网格模型,采用弹性有限元分析方法模拟计算水库蓄水至135 m1、56 m和175 m时库区地壳的垂直形变场;随后根据Farrell提出的质量负载原理产生的地壳形变理论计算库区蓄水至135 m时的库区垂直形变场;通过两种模拟方法对比可以看出变形等值线圈都包络河谷线,变形最大处都出现在香溪段,同时区域沉降是一个综合地质作用,水体的重力作用是主要诱因。     

一种基于DEM的城市平面坐标系统建立方法

随着城乡一体化进程的推进,城市建设提出了将全市域作为一个整体进行规划设计的理念.传统的基于控制点高程以及基于各县(区)建成区范围建立独立坐标系的方法,并不能全面和准确的反映全市域的投影变形情况.文中利用DEM规则格网便于读取计算的特点,提出一种适用于高海拔城市平面坐标系统建立的方法.通过遍历城市不同投影带、投影面进行变...     

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Mapping groundwater recharge potential zones in arid region using GIS and Landsat approaches,southeast Tunisia

The rapid growth of population and agricultural and industrial activities has caused an increase in demand on the Jeffara aquifers of Gabes (southeast Tunisia). In fact, the over-pumping of this aquifer system has resulted in water-level declines ranging from 0.25 to 1 m/year during the past three decades. The aim of this study is to identify favourable artificial recharge sites of this aquifer system based on the combined use of remotely sensed data, a geographic information system (GIS), the Shuttle Radar Topography Mission (SRTM) product and a multiple criteria decision making (MCDM) technique. The delineation of artificial recharge zones shows high to moderate potential for groundwater recharge (40%) in the Gabes region, with high precision of good potential proposed sites. Recharge processes need to account for natural conditions and ecosystems.     

顾及地形坡度的SRTM和ASTER加权融合

为了克服现有SRTM和ASTER各自缺陷,提升公共DEM精度,本文提出了一种顾及地形坡度的SRTM和ASTER加权融合方法。首先对两种DEM进行地理配准;然后计算不同坡度等级下SRTM和ASTER的高程误差,并得到DEM融合权重;最后采用加权平均法对SRTM和ASTER进行融合。高精度控制点的检验表明：融合后DEM精度有明显提高,相比于原始SRTM和ASTER高程误差,标准差分别降低了5.65 m和1.20 m。     

基于 SRTM DEM 的祁连山自然保护区地形特征研究

基于研究区的 SRTM DEM 模型,应用 ArcGIS10.5 空间分析模块及 Excel、SPSS 数据统计分 析功能,采用均值变点分析法确定地形起伏度的邻域分析最佳统计单元;提取了研究区高程、地形 起伏度、地形坡度、地表粗糙度和地表切割度 5 个地形因子,以分析研究区的地形特征。结果表明： 研究区地形起伏度最佳统计单元为 11 像元×11 像元（0.98 km²）,地形起伏度为 0～1 216 m。研究区 包含 13 种地貌类型,87.28%的区域为中海拔,中海拔平原、台地、丘陵为主要地貌类型。走廊南山、 冷龙岭、乌鞘岭和龙首山地平行分布,台地、丘陵穿插其中,地形复杂。研究结果为进一步探索自 然保护区的生态保护、开发利用等具体问题提供了基础数据支持。