Digital Elevation Models GLY 560: GIS and Remote Sensing for Earth Scientists Class Home Page:

5/24/2015GLY560: GIS and RS Creation of DEM’s Conversion of contour lines Photogrammetry Satellite Stereo Radar Stereo Radar Inferometry Laser Altimetry

5/24/2015GLY560: 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

5/24/2015GLY560: 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.

5/24/2015GLY560: GIS and RS Stereo Satellite Two satellite passes are combined to get effective “stereo” view

5/24/2015GLY560: GIS and RS Stereo Radar Works like photogrammetry but use radar wave instead. Can be done from space or airborne with side-looking-airborne- radar (SLAR) Can penetrate vegetation canopy

5/24/2015GLY560: 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.

5/24/2015GLY560: GIS and RS Laser Altimetry Fly laser over area, and time reflection of laser.

5/24/2015GLY560: GIS and RS Available Resolutions of DEM

5/24/2015GLY560: 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

5/24/2015GLY560: GIS and RS 10m and 30m DEM Availability

5/24/2015GLY560: 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.

5/24/2015GLY560: GIS and RS 30-minute USGS DEM Resolution: 2 arc seconds (~60m) Coverage: 30x30 min block (½ 1:100,000) Vertical Accuracy: 25 m

5/24/2015GLY560: GIS and RS 1- degree USGS DEM Resolution: 3 arc seconds (~100m) Coverage: 1x1 deg block (½ 1:250,000) Vertical Accuracy: 25 m

5/24/2015GLY560: GIS and RS “Seamless DEM” Data Buy DEM from USGS already in mosaic form by National Mapping Program

5/24/2015GLY560: GIS and RS Global DEMs GTOPO30 Aster Shuttle Mapping Program IKONOS

5/24/2015GLY560: GIS and RS GTOPO30 Resolution: 30-second (~1 km) Coverage: 50 deg lat x 40 deg long Vertical Accuracy: 30 m

5/24/2015GLY560: 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!

5/24/2015GLY560: GIS and RS Aster DEM GTOPO30 (1 km 2 /pixel) ASTER (30 m 2 /pixel)