Digital Elevation Models GLY 560 GIS and Remote

Digital Elevation Models GLY 560: GIS and Remote Sensing for Earth Scientists Class Home Page: http: //www. geology. buffalo. edu/courses/gly 560/

Creation of DEM’s • Conversion of contour lines • Photogrammetry • Satellite Stereo • Radar Inferometry • Laser Altimetry GLY 560: GIS and RS

Conversion of printed contour lines • Existing map plates are scanned • Resulting raster is vectorized and edited contours are "tagged" with elevations • Additional elevation data are created from the hydrography layer (e. g. shorelines provide additional contours) • Algorithm is used to interpolate elevations at every grid point from the contour data GLY 560: GIS and RS

Photogrammetry • Manually: an operator looks at a pair of stereophotos through a stereoplotter and must move two dots together until they appear to be one lying just at the surface of the ground • Automatically: an instrument calculates the parallax displacement of a large number of points (e. g. for USGS 7. 5 minute quadrangles, the Gestalt Photo Mapper II correlates 500, 000 points) • Correction of elevation from photographs: water bodies are assumed to be flat. GLY 560: GIS and RS

Stereo Satellite • Two satellite passes are combined to get effective “stereo” view GLY 560: GIS and RS

Stereo Radar • Works like photogrammetry but use radar wave instead. • Can be done from space or airborne with side-looking-airborneradar (SLAR) • Can penetrate vegetation canopy GLY 560: GIS and RS

Radar Interferometry • Use phase difference in two radar signals to measure elevation differences • Signals are from two receivers so called “synthetic aperture radar” or SAR. GLY 560: GIS and RS

Laser Altimetry • Fly laser over area, and time reflection of laser. GLY 560: GIS and RS

Available Resolutions of DEM GLY 560: GIS and RS

7. 5 -minute USGS DEM • Resolution: 10 m or 30 m • Coverage: 7. 5 x 7. 5 min Quad (1: 24, 000) • Vertical Accuracy: 7 m GLY 560: GIS and RS

10 m and 30 m DEM Availability http: //mcmcweb. er. usgs. gov/status/dem_stat. html GLY 560: GIS and RS

7. 5 -minute USGS DEM Data Classification Levels: • Level-1 Scanned from National High Altitude Photography (NHAP)/NAPP photography. A vertical RMSE of 7 meters is the desired accuracy standard. (Most 7. 5” DEMs are Level-1) • Level-2 Processed or smoothed for consistency and edited to remove systematic errors. A RMSE of 1/2 contour interval. • Level-3 DEMs are derived from DLG data by incorporating hypsography (contours, spot elevations) and hydrography (lakes, shorelines, drainage). A RMSE of 1/3 contour interval. GLY 560: GIS and RS

30 -minute USGS DEM • Resolution: 2 arc seconds (~60 m) • Coverage: 30 x 30 min block (½ 1: 100, 000) • Vertical Accuracy: 25 m GLY 560: GIS and RS

1 - degree USGS DEM • Resolution: 3 arc seconds (~100 m) • Coverage: 1 x 1 deg block (½ 1: 250, 000) • Vertical Accuracy: 25 m GLY 560: GIS and RS

“Seamless DEM” Data • Buy DEM from USGS already in mosaic form by National Mapping Program GLY 560: GIS and RS

Global DEMs • GTOPO 30 • Aster • Shuttle Mapping Program • IKONOS GLY 560: GIS and RS

GTOPO 30 • Resolution: 30 -second (~1 km) • Coverage: 50 deg lat x 40 deg long • Vertical Accuracy: 30 m GLY 560: GIS and RS

ASTER DEM • Advanced Spaceborne Thermal Emission and Reflection Radiometer • Off-Nadir pointing allows DEM • First international DEM of decent quality available. • Must request generation of DEM (slow turnaround) but FREE! GLY 560: GIS and RS

Aster DEM • GTOPO 30 (1 km 2/pixel) • ASTER (30 m 2/pixel) GLY 560: GIS and RS