Digital Elevation Model World Download

In late 2014, the United States government released the highest resolution SRTM DEM to the public. This 1-arc second global digital elevation model has a pixel size of about 30 meters resolution. Also, it covers most of the world with an absolute vertical height accuracy of less than 16m.

But over time, ASTER DEM data has improved its products with artifact corrections of their own. In October 2011, ASTER GDEM version 2 was publicly released, which was a considerable improvement. Despite its experimental grade, ASTER GDEM-2 is considered a more accurate representation than the SRTM elevation model in rugged mountainous terrain. But you should really take a look for yourself.

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The Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model (GDEM) Version 3 (ASTGTM) provides a global digital elevation model (DEM) of land areas on Earth at a spatial resolution of 1 arc second (approximately 30 meter horizontal posting at the equator).

A digital elevation model (DEM) or digital surface model (DSM) is a 3D computer graphics representation of elevation data to represent terrain or overlaying objects, commonly of a planet, moon, or asteroid. A "global DEM" refers to a discrete global grid. DEMs are used often in geographic information systems (GIS), and are the most common basis for digitally produced relief maps. A digital terrain model (DTM) represents specifically the ground surface while DEM and DSM may represent tree top canopy or building roofs.

There is no universal usage of the terms digital elevation model (DEM), digital terrain model (DTM) and digital surface model (DSM) in scientific literature. In most cases the term digital surface model represents the earth's surface and includes all objects on it. In contrast to a DSM, the digital terrain model (DTM) represents the bare ground surface without any objects like plants and buildings (see the figure on the right).[3][4]

The digital elevation model itself consists of a matrix of numbers, but the data from a DEM is often rendered in visual form to make it understandable to humans. This visualization may be in the form of a contoured topographic map, or could use shading and false color assignment (or "pseudo-color") to render elevations as colors (for example, using green for the lowest elevations, shading to red, with white for the highest elevation.).

Older methods of generating DEMs often involve interpolating digital contour maps that may have been produced by direct survey of the land surface. This method is still used in mountain areas, where interferometry is not always satisfactory. Note that contour line data or any other sampled elevation datasets (by GPS or ground survey) are not DEMs, but may be considered digital terrain models. A DEM implies that elevation is available continuously at each location in the study area.

One powerful technique for generating digital elevation models is interferometric synthetic aperture radar where two passes of a radar satellite (such as RADARSAT-1 or TerraSAR-X or Cosmo SkyMed), or a single pass if the satellite is equipped with two antennas (like the SRTM instrumentation), collect sufficient data to generate a digital elevation map tens of kilometers on a side with a resolution of around ten meters.[18] Other kinds of stereoscopic pairs can be employed using the digital image correlation method, where two optical images are acquired with different angles taken from the same pass of an airplane or an Earth Observation Satellite (such as the HRS instrument of SPOT5 or the VNIR band of ASTER).[19]

A tool of increasing value in planetary science has been use of orbital altimetry used to make digital elevation map of planets. A primary tool for this is laser altimetry but radar altimetry is also used.[20] Planetary digital elevation maps made using laser altimetry include the Mars Orbiter Laser Altimeter (MOLA) mapping of Mars,[21] the Lunar Orbital Laser Altimeter (LOLA)[22] and Lunar Altimeter (LALT) mapping of the Moon, and the Mercury Laser Altimeter (MLA) mapping of Mercury.[23] In planetary mapping, each planetary body has a unique reference surface.[24]

Submarine elevation (known as bathymetry) data is generated using ship-mounted depth soundings. When land topography and bathymetry is combined, a truly global relief model is obtained. The SRTM30Plus dataset (used in NASA World Wind) attempts to combine GTOPO30, SRTM and bathymetric data to produce a truly global elevation model.[30] The Earth2014 global topography and relief model[31] provides layered topography grids at 1 arc-minute resolution. Other than SRTM30plus, Earth2014 provides information on ice-sheet heights and bedrock (that is, topography below the ice) over Antarctica and Greenland. Another global model is Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) with 7.5 arc second resolution. It is based on SRTM data and combines other data outside SRTM coverage. A novel global DEM of postings lower than 12 m and a height accuracy of less than 2 m is expected from the TanDEM-X satellite mission which started in July 2010.

Where the water meets the land, coastlines are formed. Humans gravitate toward the coast with almost 40 percent of the United States total population living in coastal counties. With a large and growing population, it is critical for all coastal communities to prepare to minimize the impacts of coastal flooding events including tsunamis, sea level rise, storm surge, and hurricanes. Coastal digital elevation models (DEMs) are essential data products to help researchers and decision makers understand and predict environmental changes that affect coastal regions.

NOAA develops and uses coastal digital elevation models to support a variety of mission requirements. These include coastal flood forecasts and warnings due to tsunamis, hurricanes, and storm surge, as well as research into fish habitats, sea level changes, and off-shore energy. Accurate coastal DEMs are needed because the shape and depth of the ocean floor affects the speed and height of waves, and the coastal land surface height primarily determines the inland extent of flooding.

In the wake of Hurricane Sandy, NCEI and the U.S. Geological Survey collaboratively developed a framework to generate an accurate, consistent, and seamless national depiction of merged bathymetry and topography in the U.S. coastal zone. NCEI generates continuously updated digital elevation models (CUDEMs) that are tiled to enable targeted, rapid updates as new data become available. This framework supports a sustainable, seamless depiction of elevation from the near-shore to the Exclusive Economic Zone. CUDEMs support many different uses, such as tsunami modeling, hazard mitigation, spatial planning, habitat research, and coastal change studies.

Digital Elevation Model (DEM), Digital Surface Model (DSM) and Digital Terrain Model (DTM) are three commonly implemented geospatial features generated with UAV mapping systems. Each data product delivers different elevation values as each model uses different methodologies. Elevation values from a LiDAR point cloud come from features including bare-ground, power lines, tree canopies or buildings. Selecting the right elevation model for your project can be challenging that is why Geodetics offers the following three simplified, but common interpretations for these data products:

In forestry management, a Canopy Height Model (CHM) is a separate model derived from elevation data in the point cloud. In forested areas, the difference between the DSM and the DEM can be viewed as CHM, representing the height of trees in the area above ground-level (see figure above). Software utilizing CHMs can also derive individual tree data, such as crown diameter, crown area and tree boundaries. This is of huge value to forestry management agencies and companies, allowing for substantial cost and time savings with UAV LiDAR monitoring, relative to manual inspection of individual trees.

Once accurate classification techniques have been applied to the LiDAR point cloud, clean ground points can be targeted and isolated from the remainder of the dataset. A DEM is created by generating a mesh from the LiDAR ground points using one of several interpolation algorithms to create a jointed fabric which accurately represents the real-world ground model. Generating a DEM from a LiDAR dataset alone can uncover hidden archaeological or geological features, which may have been masked from aerial view or photogrammetric analysis by naturally occurring terrain features (a new blog coming soon will discuss how our customers successfully use the Geo-MMS LiDAR for archeology).

Several point-cloud processing software packages offer DEM/DSM generation capabilities, allowing the user to create the surface model required for their project. The only prerequisite for this is a classified LAS point cloud file. The procedure is typically straight-forward and accurate, provided the LAS file has been accurately classified. After creating an elevation model, several editing, repairing and smoothing algorithms can be applied to remove inconsistencies, sharp edges and provide a more visually appealing result. The full process can be performed in a matter of hours. User input is minimal, only requiring some basic model parameters such as curvature weight, smoothing iteration etc. Once created, the model can be colored and various layers can be toggled on/off.

A global 1-km resolution land surface digital elevation model (DEM) derived from U.S. Geological Survey (USGS) 30 arc-second SRTM30 gridded DEM data created from the NASA Shuttle Radar Topography Mission (SRTM). GTOPO30 data are used for high latitudes where SRTM data are not available. For a grayscale hillshade image layer of this dataset, see "world_srtm30plus_dem1km_hillshade" in the distribution links listed in the metadata. 2351a5e196