1. Elevation Data Sources
Technology Assessment:
Elevation Data Sources
Judy Cooper
GIS Management and Implementation
University of Texas at Dallas
October 28, 2004

2. Elevation Data What are elevation data used for?
Elevation data are used for a wide array of defense, mapping, planning and modeling purposes.
Where can you get elevation data?
Government sources:
Primary source for elevation data
Dependent on security issues (only certain data are available to public)
Data are generally free to download (though data bundles will cost you)
Commercial sources:
In general, not a source for primary data (with exception of remote sensing)
Offer customized, cleaned-up, or bundled data
What should you look for when shopping for elevation data?
Resolution
Accuracy
Currency
Completeness of coverage
Processing time required
Cost

3. US Data : USGS DEMs and NED
DEM= Digital Elevation Model
Used to produce 3-D elevation maps, data on slope/aspect; fundamental to a wide variety of environmental/ecological modeling programs
Production strategies: manually digitized from existing USGS topographic quads and converted into a raster grid format
DEM products available:
7.5 Minute DEM (30 m spacing)
2 Arc Second DEM (60 m spacing)
3 Arc Second DEM (90 m spacing)
UTM projection; NAD 27 datum
Available for free in SDTS format through
GIS Data Depot or MapMart
Updated in USGS National Elevation Dataset (NED)
1 Arc Second DEMs (30 m spacing) for all U.S. quads
Geographic projection; NAD83 datum
Seamless US coverage; most up-to-date data available
Updated bimonthly—beginning to incorporate 10 m resolution data
Available for free through Seamless Data Distribution System (SDDS)

4. Global Data : ETOPO
Compiled by cooperative effort between U.S. Naval Oceanographic Office and the Defense Mapping Agency (i.e. NIMA or NGA)
Covers terrestrial land and ocean floor for entire globe
ETOPO 5:
released in 1985
data recorded at 5 minute spacing (~10 km resolution)
ETOPO 2:
released in 2001
data recorded at 2 minute spacing (~3.6 km resolution)
incorporates new data sources (GLOBE data)
Distributed through NGDC (National Geophysical Data Center) in Boulder, CO
Available for free through download

5. Global Data : DTED DTED= Digital Terrain Elevation Data
File format is a simple, evenly spaced grid of elevation points
Created by NIMA (now NGA) and Department of Defense for military use
Geographic Coordinate System (lat/long)
Data are patchy with entire geopolitical units missing
Similar to Canadian Digital Elevation Data (CDED)
Produced at 3 Levels:
Level 0: 30 arc second spacing (~1 km resolution)
Level 1: 3 arc second spacing (~90 meters)
Level 2: 1 arc second spacing (~30 meters)
Level 0 data available for free through GIS Data Depot
DTED1 and DTED2 are not publicly available

6. Global Data : GTOPO30 Complete by USGS EROS data center in 1996
Derived from various sources including DTED and Digital Chart of the World
Covers entire world at 30 arc second spacing (~1 km resolution)
Replaced ETOPO 2/5
Less accurate than other global elevation data sets (SRTM 30, GLOBE)
Geographic coordinate system (lat/long), WGS84 datum
Download in individual tiles which include 8 separate files
USGS .DEM file structure (requires some pre-processing before viewing in ArcView)
Must merge tiles to get complete US map
HYDRO 1k: offshoot of GTOPO3
Includes additional data sets on hydrology, flow direction, drainage basins

7. Global Data : GLOBE GLOBE= Global Land One-Kilometer Base Elevation
distributed through NGDC (National Geophysical Data Center) and NOAA (National Oceanographic and Atmospheric Administration)
Completed and released 1999
Similar to GTOPO30, just newer and more accurate (in some areas)
Compiled from a variety of data sources (DTED, Digital Map of the World, etc)
30 arc second grid spacing (~ 1 km resolution)
Geographic projection (lat/long); WGS84 datum
Order in tiles (download tiles for free from NOAA website)

8. Remote Sensing : SRTM SRTM= Shuttle Radar Topography Mission
Data collected February 2000
Memorandum of Understanding between NASA and NIMA
unrestricted 3 arc-second data for entire globe
unrestricted 1 arc-second data for the U.S
restricted 1 arc-second data outside U.S.(for NASA only)
Available to public June 2003
For U.S., 30m resolution data available (same as USGS DEMs)
For North and South America, Africa, and Eurasia, 90m resolution data available (as of April 2004)
SRTM30: Global 1km data; update of GTOPO30 global DEM
End of 2005, data will meet National Map Accuracy Standards
large gaps in data (must be filled in using software tools)
Accessible through USGS Seamless Server and GLCF Earth Science Data Interface

9. Remote Sensing: ASTER
ASTER=Advanced Spaceborne Thermal Emission and Reflection Radiometer
collected from Terra spacecraft launched in 1999 as part of NASA’s Earth Observing System (EOS)
Obtains multispectral image (extract data on surface temperature, emissivity, reflectance and elevation)
contains 3 instruments of varying spectral ranges
VNIR Band 3N and 3B (nadir- and backward-looking) creates stereo pair to find height
VNIR instrument data recorded at 15m resolution
Available through NASA’s EOS Data Gateway (EDG)
Request custom datasets derived from ASTER scenes for free (including AST14DEMs at 30m resolution)
difficult file format (HDF or GeoTiff)
Important source for global data—offers same resolution as SRTM but without government restrictions

10. Remote Sensing: IFSARE
IFSARE: Interferometric Synthetic Aperture Radar for Elevation
Developed by Environmental Research Institute of Michigan (ERIM) as a Defense Advanced Research Projects Agency (DARPA) project
Sold to Intermap Technologies, Inc. in late 1990s
Interferometric radar=active X-band microwave signals
STAR-3i SAR system mounted on LearJet36A
can acquire data in all weather, atmospheric conditions, and times of day
Data collected at 2.5 m-5 m intervals (high resolution!)
3 meter vertical accuracy
UTM projection; WGS84 datum
Coverage: 7.5 minute quadrangles
Previously for government use only
Available under the NASA Scientific Data Purchase (SDP)
Last day available is October 29, 2004 (act fast!)
Available coverage: EOS/NASA test areas, Central America, Indonesia

11. Remote Sensing: LIDAR LIDAR: Light Detection and Ranging
Airborne system emits rapid pulses of laser light; connected to GPS that measures latitude, longitude, and ellipsoid height and IMU (Inertial Measurement Unit)
Flies relatively low to ground (~1 mile) to increase resolution and reduce error
Collects thousands of data points per flight swath
Records elevations for features (e.g. tree canopy) and bare earth
Difficulty mapping bare earth through dense vegetation
Can collect data at ~1 m resolution, 15 cm vertical accuracy
Cost of custom LIDAR data is $1000-$2000 (pays for flight, and data collection, processing and delivery)
Some data are available for free through the Seamless Data Distribution System

12. Bathymetric Data Commonly Used Sources:
Underwater elevations; not provided in most conventional DEMs
Data are sparse in some areas; tend to cluster around landmasses
Used for sea-faring and also used for oceanographic modeling (predict ocean currents, wave patterns, marine ecosystems, etc.)
Collection methods: multibeam sonar depth soundings from ships and sea surface height from satellite altimetry (e.g. Topex/Poseidon, Geosat)
File formats: some in DEM format; others in CDF, HDF
Commonly Used Sources:
ETOPO2
Available through NGDC
Scripps Institute of Oceanography
2 min worldwide seafloor database from satellite and depth soundings
RIDGE Multibeam Synthesis Project
Ocean floor databases; grids available for select areas
GEODAS Digital
Bathymetric Data
Produced by NGDC/NOAA; digital multibeam sonar data
Digital Bathymetric
Database Variable (DBDBV)
From U.S. Naval Oceanographic Office; 5 min. spacing

13. Custom Elevation Data
What do you do when there are no data available or you need a higher resolution?
Convert topographic contour map to elevation grid:
reverse engineering approach—not easy!
convert topographic contours to vector; vectors converted to grid through interpolation algorithm
Software assistance: ArcGIS; Global Mapper; Autodesk
Land Desktop; Able Software R2V
Order custom data:
hire engineering firm to survey area and produce elevation data files at desired resolution
Collect your own data:
collect elevation data using laser transit equipment (Total Station)-can be done at any resolution desired but very time intensive
collect elevation data using GPS units (e.g. Garmin or Trimble) but there are reported accuracy problems that may require significant pre-processing of the data

14. Data Type Advantage Disadvantage Bundle Cost USGS DEMs (30m, 60m, 90m)
Important dataset; Standard format
Derived from old survey data; patchy
TX: $100
US: $1000
USGS NED (30m)
High res., seamless, updated bimonthly
Derived from old survey data
TX: $500
US: $1200
ETOPO5
ETOPO 2
Contains sea floor elevations
Low resolution; outdated
World: $200
World: $100
DTED
Higher data quality than GTOPO30
Low resolution; incomplete coverage
GTOPO30
Once important global dataset
Low resolution; outdated/less accurate
World: $300
GLOBE
Relatively up-to-date
Low resolution; replaced by SRTM
World: $75
ASTER
High resolution data for world (potentially)
Difficult to process, database incomplete
Per Scene: $60
IFSARE
Extremely high resolution
Unavailable to public and incomplete coverage
N/A
LIDAR
Extremely high resolution and accurate
Costly; limited coverage
Custom:: $1-2K per flight
SRTM30 (1km)
SRTM (90 m)
Gaps in data, and at varying resolutions
World: $50
World: $850

15. References
Childs, J.
(2002) ASTER DEM! Edited by P. Burkhardt. Retrieved October 20, 2004 from the Geocommunity:
(2004) Digital Elevation Modeling Journal. Retrieved October 21, 2004 from:
FAS Intelligence Resource Program
(2000) Digital Terrain Elevation Data (DTED). Retrieved October 27, 2004 from:
Geoinsight
(2003) IFSARE Radar. Retrieved October 27, 2004 from:
Global Security
(2002) Interferometric Synthetic Aperture Radar - Elevation (IFSARE). Retrieved October 26, 2004 from:
Graham, William C. Jr.
(2001) A Virtual Sea. Retrieved October 24, 2004 from:
Jet Propulsion Laboratory
(2004) ASTER. Retrieved October 20, 2004 from NASA:
(2004) Scientific Data Purchase (SDP). Retrieved October 27, 2004 from NASA:
(2004) Shuttle Radar Topography Mission. Retrieved October 25, 2004 from NASA:
Land Processes Distributed Active Archive Center
(2003) HYDRO1k Elevation Derivative Database. Retrived October 24, 2004 from:
(2004) ASTER Digital Elevation Model. Retrieved October 24, 2004 from:
(2004) GTOPO30 Documentation. Retrieved October 25, 2004 from:
National Geophysical Data Center
(2004) The Global Land One-km Base Elevation (GLOBE) Project. Retrieved from Bathymetry, Topography, and Relief:
Serr, D.
(2000) Use of LIDAR in Creating Accurate Terrain Elevation Models for Floodplain Mapping. ES771 Term Project. Retrived October 20, 2004 from: U..S. Geological Survey
(2001) Digital Elevation Models. Retrieved October 24, 2004 from:
(2003) National Elevation Dataset. Retrieved October 25, 2004 from:
Virtual Terrain Project
(n.d.) Digital Elevation Data. Retrieved October 21, 2004 from: