A, 9-11 Nov. 1999
B. Csathó, and D-C. Lee,
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185-2200.
International Archives of Photogrammetry and Remote Sensing, Vol. 32, Part 3W14, La Jolla, CA, 9-11 Nov. 1999
APPLICATION OF THE SHUTTLE LASER ALTIMETER IN AN ACCURACY ASSESSMENT OF GTOPO30,
A GLOBAL 1-KILOMETER DIGITAL ELEVATION MODEL
David J. Harding’, Dean B. Gesch”, Claudia C. Carabajal, and Scott B. Luthcke*
'NASA/Goddard Space Flight Center (Code 921), Greenbelt, MD 20771, harding@denali.gsfc.nasa.gov
Raytheon ITSS, @ USGS/EROS Data Center, Sioux Falls, SD 57198, gesch@edcmail.cr.usgs.gov
3NVI, Inc., @ NASA/Goddard Space Flight Center (Code 926), Greenbelt, MD 20771, claudia@stokes.gsfc.nasa.gov
“Raytheon ITSS, @ NASA/Goddard Space Flight Center (Code 926), Greenbelt, MD 20771, sluthcke@ geodesy2.gsfc.nasa.gov
KEYWORDS: Shuttle Laser Altimeter, GTOPO30, global, topography, DEM, elevation, accuracy.
ABSTRACT
Continental-scale topographic profiles between 28.45° N and S latitudes acquired by the first flight of the Shuttle Laser Altimeter
(SLA) experiment are used to evaluate the vertical accuracy of GTOPO30, a global digital elevation model with a grid spacing of
approximately 1 km. GTOPO30 is a compilation of eight sources of elevation information, including raster and vector data sets. The
mean and standard deviation of SLA to GTOPO30 elevation differences are computed for Africa, southern Asia, central South
America, and Australia. Variations in mean differences between continental regions and GTOPO30 sources indicate that there are
vertical datum discrepancies incorporated in GTOPO30 on the order of 10 m. Variation in the standard deviation of the differences
confirms that raster sources in GTOPO30 are more accurate than vector sources.
1. INTRODUCTION
Digital Elevation Model (DEM) compilations of the Earth’s
land topography at a grid spacing of approximately 1 km have
recently become available publicly. These include two products
distributed by United States federal agencies, GTOPO30 from
the Geological Survey (USGS) and GLOBE from the National
Atmospheric and Oceanic Administration. These data have
great utility in regional and continental scale studies requiring
topographic data and are a significant advance upon previously
available global topographic data sets. However, the vertical
accuracy of these compilations is variable and poorly quantified
because the elevation measurements have been assembled from
numerous topographic sources of varying, and uncertain,
quality. Significantly, the compilations include sources using
disparate and poorly documented reference ellipsoids and
datums; thus, the DEM’s are not internally-consistent, geodetic
representation of the Earth's surface.
Profiling laser altimeter observations from orbital platforms
provide the opportunity to obtain elevation data of very high
vertical accuracy in a consistent, Earth-centered reference frame
(Harding et al., 1994). Laser altimeters are particularly well
suited to measuring land topography, as comparing to radar
altimeters, because of the ability to use smaller footprints that
have no difficulty ranging to complex, high-relief terrain. Also,
the optical backscatter return can be used to establish the
surface height distribution within the laser footprint and
differentiate features at multiple heights such as vegetation
canopy layers and the underlying ground. Orbital profiling
altimeter data lack the sampling density necessary to construct
DEM's with spatial resolutions comparable to those derived
utilising orbital stereoscopic or interferometric capabilities.
However, they do provide data very well suited to evaluating
the accuracy and error characteristics of global DEM's
constructed by other means. Here we us data from the first
flight of Shuttle Laser Altimeter (SLA-01) to evaluate one of
the global 1 km DEM's, GTOPO30, providing an independent
assessment of that product’s quality.
11. GTOPO30
GTOPO30 is a global DEM resulting from a collaborative effort
led by the staff at the USGS's EROS Data Center (EDC).
GTOPO30 was developed over a three-year period and
completed in 1996. Elevations are regularly spaced at 30 arc
seconds (approximately 1 kilometre). GTOPO30 was
developed to meet the needs of the geospatial data user
community for regional and continental scale topographic data.
The horizontal co-ordinate system is latitude and longitude
referenced to WGS84. The vertical units represent elevation in
meters above mean sea level. GTOPO30 is based on data
derived from eight sources of elevation information, including
raster and vector data sets.
The raster data sets include Digital Terrain Elevation Data
(DTED) and USGS 1-degree DEM’s, both gridded at 3 arc
seconds (approximately 90 m), and a New Zealand DEM
gridded at 500 m. DTED is produced by the U.S. National
Imaging and Mapping Agency (NIMA) and the USGS DEM’s
are primarily reformatted versions of DTED. In areas lacking
raster data, the primary data source was the Digital Chart of the
World (DCW), a vector cartographic data set based on the
1:1,000,000-scale Operational Navigation Chart (ONC) series.
Some areas are based on digitised versions of 1:1,000,000 scale
paper maps from the Army Map Service (AMS), the
International Map of the World (IMW), and the Peruvian
government. Coverage for Antarctica was included using the
Antarctic Digital Database (ADD). The GTOPO30 data sources
and the processing methods used to assemble them are detailed
