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Image and Map Data for Global DEMs
R. Welch
Center for Remote Sensing and Mapping Science (CRMS)
Department of Geography
The University of Georgia
USA
Digital elevation models (DEMs) are used in scientific research involving the Earth's land surface.
These DEMS are also required for geometric, radiometric and atmospheric corrections of satellite
image data used to derive global land cover/use information. Although relatively coarse DEMs such
as the NOAA National Geophysical Data Center's Worldwide Digital Terrain Data Set and the Digital
Chart of the World have been produced from existing topographic maps of the globe, the accuracy
and completeness is variable (Row and Hastings, 1994). Sensors such as the Advanced Spaceborne
Thermal Emission and Reflection Radiometer (ASTER), being built by the Japanese for installation
on the first of NASA's Earth Observation System (EOS AM-1) platforms in 1998, will provide a new
source of topographic data for deriving global DEMs (Kahle, et al., 1991; Arai, 1992; Welch and
Lang, 1994).
The ASTER system has stereo imaging capability. Its nadir (3N) and aft-viewing (3B) telescopes
(27.7. off-nadir) in the near infrared band (0.76-0.86 4A m) provide a B/H ratio of 0.6 and an
instantaneous-field-of-view (IFOV) of 15 m over a 60-km swath width. With an orbital inclination
of 98.2" for the EOS AM-1 platform, ASTER is capable of acquiring a maximum of 771 stereo
scenes per day and during its planned 5-year mission should be able to record the 45,000 cloud-free,
digital stereopairs that are required for one time coverage of the Earth's entire land surface.
The production of DEMs from ASTER stereo data is based on photogrammetric principles for the
automated stereocorrelation of stereopairs of images in digital format - as previously demonstrated
with Landsat Thematic Mapper (TM), SPOT HRV, JERS-1 OPS and German Spacelab D2 MOMS-
02 data (Ehlers and Welch, 1987; Maruyama, et al., 1994; Konecny, et al., 1994). With adequate
ground control points, it is anticipated that ASTER DEMs are expected to have planimetric errors of
about + 10-15 m and vertical errors of = 20-30 m.
It is conservatively estimated that ASTER DEMs will be useful for mapping at scales of 1:100,000 to
1:250,000 in most instances, and perhaps at scales of 1:50,000 in favorable circumstances. The
images and DEMs will be integrated with global-scale models to facilitate broad-scale scientific
investigations and contribute to the understanding of global processes.
References
Arai, K., 1992. Accuracy assessment of DEM with EOS-a/ASTER, Department of Information
Science, Saga University, Japan, Unpublished report to the ASTER DEM Working Group, 9
PP-
Ehlers, M. and R. Welch, 1987. Stereocorrelation of Landsat TM images, Photogrammetric
Engineering and Remote Sensing, 53(9): 1231-1237.
