China
Africa
Explore chapters and articles related to this topic
Petroleum Geological Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
The presentation of geological features in the form of mapping is a well-established technique. Broadly the earth’s surface (land and sea bottom) and underground structures are studied separately. The study of the earth’s surface is called topography. The data are presented by ‘topographic mapping’. The geological subsurface data indicating the underground features are processed and presented by graph and ‘geological mapping’. The topographic mapping and geological mappings are different kinds of presentations but are related to each other. Topographic mapping deals with visible surface features and objects, whereas geological mapping is concerned with hidden underground features.
Utilization of groundwater vulnerability maps to assess aquifer pollution potential
Published in M.M. Sherif, V.P. Singh, M. Al-Rashed, Hydrology and Water Resources, 2020
Topography refers here to the slope variability of the land surface. The degree of slope will determine the extent of runoff of the pollutant and settling long enough to infiltrate. The digital elevation model (GTOPO30-DEM) was used to extract the slope of the study area (Fig. 5).
Remote Sensing
Published in Julio Sanchez, Maria P. Canton, William Perrizo, Space Image Processing, 2018
Julio Sanchez, Maria P. Canton
Local factors of an image feature are often termed context operators. Elevation is probably the most commonly used context operator. Topographic maps show lines that link points of the same elevation. A digital elevation model (DEM) is the computerized version of a topographic map. Neighborhood factors are also considered context operators and new layers are derived taking into consideration neighborhood and proximity conditions. For example, Figure 1.11 shows a new boolean layer b which is based on selecting the larger lakes and ponds in image a. In this case, the processing logic uses a neighborhood algorithm to determine if a group of related pixels meets the size requirement specified in the filter. Such digital filters are often available in a GIS and in other raster image processing products.
Forest roads: regional perspectives from around the world
Published in International Journal of Forest Engineering, 2023
C Kevin Lyons, Stelian Alexandru Borz, Campbell Harvey, Muedanyi Ramantswana, Hideo Sakai, Rien Visser
In Japan, frequent heavy rainfall is correlated with road failures and makes drainage of the road surface indispensable. It is essential to construct robust, cost-efficient, and well-maintained road networks. Light detection and ranging technology (LiDAR) can precisely measure the topography. A watercourse map estimated from a digital elevation model based on LiDAR data can be used to identify changes to watercourses after construction of forest roads (Yoshida et al. 2019). Bloser et al. (2012) describe using rubber belts to divert water off the surface of low-volume roads. Belt diversion consists of a piece of used conveyor belt bolted to treated lumber; the lumber is buried in the road and the belt extends above the road surface and is angled to direct water flowing along the road surface off the road. Rubber belt diversion is used for spur roads in Japan. Rolled grade without belt diversion is also attempted in Japan. Oohashi (2011, 2015) described the rolled grade as a road grade that is climbing when crossing valleys and dropping when crossing ridges. The objective of the rolled grade is to encourage cross-road drainage on to ridges that tend to be better drained and water shedding (Keller and Sherar 2003).
Global DEMs vary from one to another: an evaluation of newly released Copernicus, NASA and AW3D30 DEM on selected terrains of China using ICESat-2 altimetry data
Published in International Journal of Digital Earth, 2022
Hui Li, Jiayang Zhao, Bingqi Yan, Linwei Yue, Lunche Wang
Digital Elevation Model (DEM) is a quantitative representation of the topography. It is essential for a broad range of elevation-related studies, such as glacial mass balance (Berthier et al. 2007), flood inundation mapping (Saksena and Merwade 2015), landform classification (Li et al. 2012) and Earth surface process modeling (Tarolli 2014). With the rapid evolvement of DEM generation techniques, an increasing number of DEM datasets have been made available in the past two decades, ranging from localized high-resolution DEMs (i.e. LiDAR DEM) to middle-resolution global DEMs (GDEM) (Liu 2008; Grohmann 2018). Although high resolution DEMs are of high accuracy, they are only limited to relatively few developed countries, accounting for approximately 0.005% of the Earth’s land area (Hawker et al. 2018). Therefore, spaceborne GDEMs generated from radar and optical sensors are the only source of elevational information for most areas of the world.
Use of improved DRASTIC model for groundwater vulnerability assessment of upper Alwar district of Rajasthan state
Published in ISH Journal of Hydraulic Engineering, 2021
Hansa Rajput, Arpit Kumar, Rohit Goyal
Topography is the arrangement of the natural and physical features of an area. Slope of any area can be obtained from the digital elevation model of that area. The water will flow over high slopes due to gravity and will be retained in the area of low slope for a greater period of time. This provides greater potential of contaminant movement into the ground. Topography of the area decides whether the contaminant will flow over or will stay on the surface for a sufficient time to cause infiltration (Aller et al. 1987).