Digital Elevation Models And Relief Models 1DEM

Part 1: The Underlying Elevation Data 2DEM

Digital Elevation Models are: Data files that contain the elevation of the terrain over a specified area, usually at a fixed grid interval The intervals between each of the grid points will always be referenced to some geographical coordinate system. (e.g. latitude-longitude, UTM, SP). The closer together the grid points are located, the more detailed the information will be in the file. The details of the peaks and valleys in the terrain will be better modeled with a small grid spacing than when the grid intervals are very large. Elevations other than at the specific grid point locations are not contained in the file. As a result peak points and valley points not coincident with the grid will not be recorded in the file. The DEM file also does not contain civil information such as roads or buildings. It is not a scanned image of the paper map (graphic). It is not a bitmap. The DEM does not contain elevation contours, only the specific elevation values at specific grid point locations. (SEE NEXT SLIDE FOR EXAMPLE) source: 3DEM

Digital Elevation Model: What it looks like Lay a grid over some part of the world and find the average elevation in each cell 4DEM

cell size cell (cell value) Cell Definition The size of a cell is in either: meters, feet, degrees, or arc seconds 5DEM

DEM Data Sources Primary Data Sources: Shuttle Radar Topography Mission (SRTM) or other airborne sensors Secondary Sources from existing maps: 30m DEMs from 1:24,000 scale map 1” (arc second ) National Elevation Dataset 3" (100m) DEMs from 1:250,000 scale maps 30" DEM of the earth (GTOPO30) 6DEM

Primary Data Source Generation: Space Shuttle 7DEM

Shuttle Radar Topography Mission (SRTM) 1 arc-second elevation data for the United States, 3 arc-second data for the globe Produced by radar measurements from a Shuttle mission, Feb , ta/obtainingdata.html 8DEM

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Santa Barbara, California 10DEM

San Andreas Fault, California 11DEM

Salt Lake City, Utah 12DEM

Mt Kilimanjaro, Tanzania 13DEM

Interferometry used by SRTM In interferometry, two images are taken from different vantage points of the same area. The slight difference in the two images allows scientists to determine the height of the surface. 14DEM

Secondary Data Source Generation: Using USGS Topographic Maps 15DEM

200 Meter Mesh (Universal Transverse Mercator Coordinates) 1km 16DEM

100 Meter Mesh (UTM Coordinates) 100m 1km 17DEM

30 Meter Mesh Standard for 1:24,000 Scale Maps 18DEM

DEM Lattice Points 19DEM

DEM Cell Stores Elevation at Lattice Point 20DEM

DEM Elevations Contours DEM

Cell Size 30m100m Comparison 22DEM

30m DEMs Best resolution standardized data source available for the US Coverage of the country is incomplete Data by 7.5’ map sheets in UTM projection Link for US Link 23DEM

National Elevation Dataset Seamless 1” DEM for the US in 1° x 1° blocks Compiled by synthesizing the 30m DEM’s from 1:24,000 scale maps Link to website Link 24DEM

Part 2: Representation of elevation data 25DEM