NGS’ GPS Height Modernization Activities

David B. Zilkoski

Abstract:	Today, state and local governments spend tens of millions of dollars each year correcting engineering projects that are continually affected by changing land surfaces due to subsidence, crustal plate movements of the earth, floods, earthquakes, and other natural phenomena. For example, the Northridge, California, earthquake in 1994 required more than $1 million in Federal government expenditure for the extensive resurveying that had to be done as a result of the earthquake. Heights determined using GPS are now accurate within the range needed by most users, i.e., 2-cm, when NGS-developed guidelines are employed. Many projects can be accomplished using GPS at 20% to 50% of the costs of using classical methods. The indirect costs associated with the inability to adjust for elevation change may result in even greater costs. Examples include: - Crop irrigation can be rendered inefficient, wasting the use of available water and increasing the demand for more infrastructure to divert limited water supplies. - Storm drainage management can become less predictable, resulting in higher insurance rates and a greater need to build additional storm sewers. The North American Vertical Datum of 1988 (NAVD 88), when implemented with GPS technology, offers significant benefits to the nation in terms of dollars and lives saved. To document its utility and worth to the nation, NGS conducted a study to evaluate the technical, financial, legal, and economic aspects of modernizing the national height system with GPS. The applications of this break-through national positioning system can provide: - Improved aircraft navigational aids, and safer approach and landing procedures; - Advanced surface transportation control and monitoring; - Safer marine navigation tools and products; - Highly efficient fertilizer and pesticide spreading, resulting in reduced run-off water pollution; - More accurate modeling of storm surge and pollution trajectories; - Increased accuracy for improved resource management decision making; - Significant time savings in field surveying; and - Improved disaster preparedness and earthquake monitoring. NGS has been successfully using GPS in support of modernizing the national height system. This report briefly describes some of these activities.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	943 - 954
Cite this article:	Zilkoski, David B., "NGS’ GPS Height Modernization Activities," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 943-954.
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