Surface area processing in GIS for different mountain regions

Surface area is a fundamental parameter derived from terrain analysis in geographical information systems (GIS) for modeling the real world. Therefore, an evaluation of the techniques implemented by GIS models is important in order to obtain reliable area measurements. The study compares two raster-based methods with a TIN-based (triangulated irregular network) method for surface area approximation using a digital elevation model (DEM) with 25 m × 25 m resolution in six mountain regions of Shandong Province, China. Raster-based method Ⅰ calculates surface-area grids from DEMs directly. Eight 3-dimensional triangles connecting the center point of each cell with the center points of the eight surrounding cells are generated and then the areas of the portions of each triangle that lay within the cell boundary are calculated and summed. Raster-based method Ⅱ produces the surface area of each cell directly from the pixel size and the slope value for the pixel. The results demonstrate that the surface areas calculated by raster-based method Ⅰ are equal to those of the TIN-based method. The results of raster-based method Ⅱ are the lowest but the difference in areas between the two raster-based methods decreases with the decrease in terrain complexity. Compared to the method with TINs, raster-based method Ⅱ can do better because it has some advantages, such as neighborhood analysis, more consistent output and faster processing speed. The results also demonstrate that the difference between surface and horizontal areas should be considered if more than 30% of the area of a region has slopes steeper than 18.2 degrees.     

Enhancing the Simplified Surface Energy Balance (SSEB) approach for estimating landscape ET: Validation with the METRIC model

Evapotranspiration (ET) can be derived from satellite data using surface energy balance principles. METRIC (Mapping EvapoTranspiration at high Resolution with Internalized Calibration) is one of the most widely used models available in the literature to estimate ET from satellite imagery. The Simplified Surface Energy Balance (SSEB) model is much easier and less expensive to implement. The main purpose of this research was to present an enhanced version of the Simplified Surface Energy Balance (SSEB) model and to evaluate its performance using the established METRIC model. In this study, SSEB and METRIC ET fractions were compared using 7 Landsat images acquired for south central Idaho during the 2003 growing season. The enhanced SSEB model compared well with the METRIC model output exhibiting an r² improvement from 0.83 to 0.90 in less complex topography (elevation less than 2000 m) and with an improvement of r² from 0.27 to 0.38 in more complex (mountain) areas with elevation greater than 2000 m. Independent evaluation showed that both models exhibited higher variation in complex topographic regions, although more with SSEB than with METRIC. The higher ET fraction variation in the complex mountainous regions highlighted the difficulty of capturing the radiation and heat transfer physics on steep slopes having variable aspect with the simple index model, and the need to conduct more research. However, the temporal consistency of the results suggests that the SSEB model can be used on a wide range of elevation (more successfully up 2000 m) to detect anomalies in space and time for water resources management and monitoring such as for drought early warning systems in data scarce regions. SSEB has a potential for operational agro-hydrologic applications to estimate ET with inputs of surface temperature, NDVI, DEM and reference ET.     

帽儿山的潜在沟系分析及其应用

定义了潜在沟系的概念，并将帽儿山的潜在沟系分为平行沟、陡坡显沟和平坦沼泽三种类型。同时应用ARCVIEW GIS的空间分析系统对帽儿山的潜在沟系进行了计算，结果发现：帽儿山的潜在沟系与现有沟系图非常相似，而潜在沟系比现有沟系图更细致地刻画了帽儿山的沟系特征。     

Soil Phosphorus and Potassium Mapping Using a Spatial Correlation Model Incorporating Terrain Slope Gradient

Variable-rate fertilizer application requires knowledge of the spatial distribution of soil nutrients within fields. Grid soil sampling might be used for acquiring this information, but is often too expensive for resolving spatial patterns in soil nutrients at the scale of precision fertilizer application. The objective of this study was to determine whether grid sampling efficiency can be improved using cokriging estimates with slope gradient as a secondary variable, which is easily obtained from high-resolution digital elevation models. Soils in two northern Montana wheat fields were sampled at the nodes of a 100-m diagonal grid. Soil test phosphorus and potassium maps were constructed with kriging and cokriging. Co-kriging uses the spatial correlation between two variables to predict for the less intensively sampled variable of interest, often with less estimation error than a univariate method such as kriging. The average estimation variance for cokriging compared to kriging was reduced for all values of the correlation considered. The additional complexity of cokriging might be justified provided a secondary variable exists that is spatially cross correlated with the primary variable of interest.     

基于DEM的秦岭火地塘森林植被空间变异分析

DEM是G IS空间分析的基础,在林业生产及科研领域中开始得到广泛应用。以秦岭火地塘林场为研究对象,利用DEM对火地塘林场森林植被类型在不同地形因子上的分布规律进行统计和分析。结果表明,火地塘森林植被类型在垂直分布中具有明显的海拔梯度性,其中桦木明显处于高海拔地带;阳坡森林植被类型生长较好,部分植被在坡向上平均分布;所有森林植被平均分布于坡度为15~°35°之间,这一分布状况与火地塘地形有很大关系。     

Investigation on pistachio distribution in the mountain regions of northeast Iran by ALOS

Iran supports five different vegetation zones. One of those is the Irano-Touranian zone that is located in the northeast of Iran. This vegetation zone includes arid and semi-arid lands, and its area is about 3.5 million hm². It supports growth of pistachio (Pistacia vera), a deciduous-broadleaved species, which is one of the ecologically and economically most important native species. In this study, we analyzed three images acquired by ALOS satellite, including 10m resolution multispectral band (AVNIR-2), 2.5 m resolution “Backward” PRISM image, and 2.5 m resolution “Nadir” PRISM image, based on a provided rational polynomial coefficient (RPC). Using the “Backward” and “Nadir” images, a 2.5 m resolution digital elevation model (DEM) was produced. Four methods with AVNIR-2 and PRISM data were used to produce pan-sharpening images and conduct an object-based feature extraction process. Normalized Difference Vegetation Index (NDVI) was used to determine the maximum distribution of pistachio in related elevation. The accuracy of the DEM was tested on 28 ground control points in the pair image as tie points, with the value of parallax error of 0.9027 m. The created elevation map indicated that pistachio trees grow up at 650m above sea level (a.s.l.). The result from NDVI in the related elevation showed the maximum density of pistachio at 800m a.s.l. In addition, the result of feature extraction in the forest showed the area of each target element calculated. The results of this research will improve decision-making and lead to sustainable management in general.     

帽儿山虚拟林相的构建

应用帽称山林场1999年的遥感调查结果建立了DEM（Digital Elevation Model）、优势树种的分布图以及虚拟林相。其目的在于建立一种信息载体，将森林资源信息更形象、直观、动态地反映给使用者，使其既有亲临其境的感觉又能方便、快捷地查询各种信息。帽儿山虚拟林相建立的结果表明，森林资源信息也可以在微型计算机上表达和处理。     

基于渭河下游DEM的洪水淹没分析与模拟

基于数字高程模型的栅格结构，以渭河下游洪水淹没数据为基础，依据无源淹没和有源淹没的原理，并结合ERDAS8．5的虚拟GIS模块实现了无源淹没的三维可视化模拟。初步演示了洪水泛滥时的动态淹没过程，促使相关部门高度重视治洪工作。并给政府制定防洪、治洪措施提供了理论依据，从而为进一步开展治洪工作开拓了更广阔的前景。     

温度植被干旱指数反演全国土壤湿度的DEM订正

 用温度植被干旱指数(TVDI)反演土壤湿度的原理,是基于水分蒸发和植被蒸腾对地表温度的降低作用。随高程增加气温降低,气温影响地表温度,因而随高程增加气温对地表温度也有一定的降低作用。用数字高程模型(DEM)对地表温度t s进行订正,可以减少气温对地表温度的影响,使得经过DEM订正获取的TVDI,能更好地反映土壤湿度。订正前后结果的对比分析也表明,经过DEM订正获取的温度植被干旱指数,与实测值有更好的相关性,能更好地反映土壤湿度分布的实际情况。     

水系标志在大兴安岭中生代火山岩识别中的应用

水系类型、发育程度及组合状态可以直观反映一定的岩石类型与地质构造特点。基于大兴安岭研究区数字高程模型(DEM)数据通过D8算法对该地区水系进行提取,并经过与1∶50 000遥感影像叠加对比,结果表明基本吻合,提取效果理想,水系级别达到五级以及对1∶50 000遥感影像水系提取可以利用同区DEM代替。通过分析判断水系形式的发育特征,对区内岩石类型的划分和构造进行了准确的解译,取得显著且准确的成果。