Digital Elevation Models
GLY 560:
GIS and Remote Sensing for
Earth Scientists
Class Home Page:
http://www.geology.buffalo.edu/courses/gly560/
Creation of DEM’s
• Conversion of contour lines
• Photogrammetry
• Satellite Stereo
• Radar Stereo
• Radar Inferometry
• Laser Altimetry
4/13/2015
GLY560: 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
4/13/2015
GLY560: 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.
4/13/2015
GLY560: GIS and RS
Stereo Satellite
• Two satellite
passes are
combined to get
effective “stereo”
view
4/13/2015
GLY560: 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
4/13/2015
GLY560: 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.
4/13/2015
GLY560: GIS and RS
Laser Altimetry
• Fly laser over area, and time reflection of
laser.
4/13/2015
GLY560: GIS and RS
Available Resolutions of DEM
4/13/2015
GLY560: 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:
7m
4/13/2015
GLY560: GIS and RS
10m and 30m DEM Availability
http://mcmcweb.er.usgs.gov/status/dem_stat.html
4/13/2015
GLY560: 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.
4/13/2015
GLY560: GIS and RS
30-minute USGS DEM
• Resolution:
2 arc seconds (~60m)
• Coverage:
30x30 min block (½ 1:100,000)
• Vertical Accuracy:
25 m
4/13/2015
GLY560: GIS and RS
1- degree USGS DEM
• Resolution:
3 arc seconds (~100m)
• Coverage:
1x1 deg block (½ 1:250,000)
• Vertical Accuracy:
25 m
4/13/2015
GLY560: GIS and RS
“Seamless DEM” Data
• Buy DEM from USGS already in mosaic form by
National Mapping Program
4/13/2015
GLY560: GIS and RS
Global DEMs
• GTOPO30
• Aster
• Shuttle Mapping Program
• IKONOS
4/13/2015
GLY560: GIS and RS
GTOPO30
• Resolution:
30-second (~1 km)
• Coverage:
50 deg lat x 40 deg long
• Vertical Accuracy:
30 m
4/13/2015
GLY560: 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!
4/13/2015
GLY560: GIS and RS
Aster DEM
• GTOPO30
(1 km2/pixel)
4/13/2015
• ASTER
(30 m2/pixel)
GLY560: GIS and RS