Chapter 1. Executive Summary

This is the first version of documentation for the Global Land One-kilometer Base Elevation (GLOBE) data set. GLOBE is an internationally designed, developed, and independently peer-reviewed global digital elevation model (DEM), at a latitude-longitude grid spacing of 30 arc-seconds (30"). This report describes the history of the GLOBE project, the candidate data sets, data compilation techniques, organization, and use of the data base. The data are available on CD-ROM and the World Wide Web.

The previous standards for global digital elevation models (DEMs) are ETOPO5 (NGDC, 1988) and TerrainBase (Row and Hastings, 1994; Row and others, 1995), which were at 5 arc-minute (5') gridding. Higher resolution DEMs exist for parts of the world (Gittings, 1997). However, when GLOBE was conceived, no DEM of higher resolution was known that covered more than two-thirds of Earth's land surface. That DEM (NIMA, various dates) and most higher-resolution DEMs outside the United States are restricted by copyright or other limitation on their distribution.

Two global DEMs have been produced at 30" gridding during the design and development of GLOBE. The Jet Propulsion Laboratory, a Federally-funded Research and Development Center operated by the California Institute of Technology for the National Aeronautics and Space Administration (NASA), developed a DEM from Digital Terrain Elevation (DTED) and other sources, for internal use in support of NASA satellite missions. Separately, the U.S. Geological Survey developed a DEM called GTOPO30. Both of these data sets have provided important pieces of GLOBE Version 1.0. However, GLOBE Version 1.0 differs from such projects:

• Additional contributions have been made directly to GLOBE, and to the National Oceanic and Atmospheric Administration's (NOAA's) long-standing program in international digital elevation data. Eighteen (18) combinations of data source/lineage have been mosaicked and described.
• GLOBE is an ongoing program of data collection, with enhancement of the data base and documentation for as long as the data are useful.
• GLOBE is an active program to enhance access to the data. This includes evolving improvements to the GLOBE Web site, and to CD-ROM and other possible distributions of GLOBE data. This also includes plans to make available many source DEMs, not just the final GLOBE mosaic, plus documentation.

GLOBE data are suitable for many regional and continental applications, such as:

• Design for communications infrastructure (such as cellular communications networks and radio/television broadcast antenna systems) in the absence of higher-resolution data. For example, the U.S. Federal Communications Commission certified 30" data for the conterminous United States for such purposes. The data have been distributed for almost two decades by NOAA's National Geophysical Data Center (NGDC).
• Logistical design for other civil works in remote areas, in the absence of higher-quality data.
• Development of flight safety systems (navigational aids, terrain avoidance aids, etc.). Note that such critical applications require careful adaptation of DEMs with current levels of quality.
• Processing of satellite data such as geometric and atmospheric correction of medium and coarse resolution satellite image data (Gesch, 1994; Jet Propulsion Laboratory, 1998, in press), as well as initial geometric correction of higher-resolution satellite data.
• Various forms of environmental study, such as climate modeling, continental-scale land cover mapping, and extraction of drainage features for hydrologic modeling (Danielson, 1996; Verdin and Greenlee, 1996).
• "Validation" of future global DEMs (especially when the candidates for GLOBE are also used) and of future regional DEMs lacking better, available regional DEMs for the same region.
  

Caveats: Note that GLOBE Version 1.0, like other digital topographic data, are insufficiently accurate over their full global extent to be taken too literally for mission-critical applications. They must always be interpreted with extreme caution. They should not be used exclusively in mission-critical or life-critical applications. Nevertheless, GLOBE Version 1.0, with its present 30" gridding, multiple sources, and documentation designed to inform users of the character of such data, is a remarkable improvement over previously available data and ancillary materials. It greatly exceeds the original expectations of its developers. This document contains discussions about data quality; caveats are concentrated in Sections 6 and 12 of this report.

GLOBE remains in active development. Peer review continues to be an integral part of the GLOBE process; please see our peer review site on the World Wide Web linked from http://www.ngdc.noaa.gov/mgg/topo/globe.html. Future versions of GLOBE should be even more valuable, as they are expected to include:

• Additional improved elevation data
• Global bathymetric coverage
• Multiple indices (such as quasi-maximum and quasi-minimum elevations as well as representative values) where available
• Multiple source files and documentation designed so that the user may be able to develop custom DEMs

GLOBE has been creative in negotiating ways to release new DEMs to the public:

• The GLOBE project negotiated the first public release of the previously restricted Digital Terrain Elevation Data (DTED) from the Defense Mapping Agency (now the National Imagery and Mapping Agency). DTED Level 0 was initiated as a joint DMA/GLOBE design, and was contributed to NGDC for GLOBE.
• The GLOBE project negotiated development of non-copyright derivations from copyright DEMs. This has involved joint design of a DEM with lower horizontal and/or vertical resolution or a different datum or map projection than is subject to local copyright requirements. The resultant DEM is still valuable as part of the GLOBE compilation.
• GLOBE has developed creative licensing agreements with sources of high-resolution data, allowing high-quality data that must be kept under copyright to still be accessible.

GLOBE cites sources of data, and can mention, when appropriate, that certain sources can directly supply higher quality data. We hope you will contact the GLOBE Secretariat about the benefit to yourselves (and the public) from contributing to the GLOBE data base. Please contact:

Participants in the GLOBE Task Team are noted in Section 2.C and in Appendix A.

Note: The Web-based version of this documentation will receive more frequent updates than the printed version. Bookmark http://www.ngdc.noaa.gov/mgg/topo/report/.