NATIONAL HEIGHT MODERNIZATION

Problem: 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.

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.
Use of the 750,000 precisely located, in-ground or monumented reference points installed over the past 200 years to measure heights is not by itself adequate to meet the needs of today's mobile and technology-driven society. The classical line-of-sight measurements do not provide the real-time accuracy needed for today's positioning technologies and applications, including precision agriculture, efficient marine transportation, and zero visibility landings of aircraft.

Solution: Through the use of the Global Positioning System (GPS), a constellation of 24 high altitude (11,000 miles) NAVSTAR satellites operated by the U.S. military and originally designed for use as an advanced weapons delivery system first deployed in the 1980's, pinpoint positioning accuracies can be provided 24 hours a day. The combination of an improved national height system (North American Vertical Datum of 1988) first adopted by the Federal government in 1993, along with the positioning technology of GPS, offers the nation and its governments, for the first time, the ability to obtain precise vertical measurements in real-time.

Applications: Integrating the horizontal, vertical, and gravity control networks into a unified national positioning system, joined and maintained by GPS, and administered by the National Geodetic Survey, sets the stage for many advances . A state-of-the-art National Spatial Reference System, with NAVD 88 as its elevation reference, can make available to the nation a common, consistent set of real-time geographical coordinates, or reference points. 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;
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 detection.
Proposal: If implemented, NAVD 88 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, Congress approved for fiscal year 1998 an appropriation of $1.0 million to conduct a study to evaluate the technical, financial, legal, and economic aspects of modernizing of the national height system with GPS.