The Global Positioning System (GPS) has made possible a revolution in the art of navigation, positioning, and surveying. In September 1988, NCHRP contracted for research by GPS Services, Inc. and the National Geodetic Survey Division of Charting and Geodetic Services of the National Ocean Service, National Oceanic and Atmospheric Administration, to improve the civilian applications of the GPS in land surveying. The NCHRP-funded research originally concentrated on using differential GPS techniques to determine the kinematic position of a moving antenna--continuous, uninterrupted contact with satellites and a reference antenna/receiver being required.

A recently developed ambiguity function technique--more accurately described as a rapid-static technique rather than a kinematic GPS technique because the moving antenna is not in continuous contact with the satellites when it is moving between monuments--was subsequently investigated by the researchers. The principal benefits of this technique are the speed and accuracy with which it may be used and its immunity to cycle slips or other discontinuities in the phase data that commonly occur. The technique requires measurements from only a single epoch (instant in time) but, in practice, monument occupations of 1 to 2 min are more common.

As part of this project, OMNI--a computer program created by the National Geodetic Survey Division--was enhanced by using the ambiguity function technique described previously for phase initialization that depends only on phase measurements. This technique can work using either the data from only a single epoch or averaged data from several epochs. The conditions required to use this technique on a single epoch will be met by the complete GPS constellation and any dual-frequency receiver capable of tracking seven or more satellites. However, rapid-static applications may make use of single- or dual-frequency receivers and require fewer satellites if multiple occupations of a monument are feasible.

Research is complete. Research Results Digest 185, "NCHRP Supports Advances in Differential GPS Satellite Surveying," provided a preliminary announcement on the availability of software. Subsequently, more complete document was submitted and an updated Research Results Digest 199, "Rapid Static Surveying Using the Global Positioning System," is now available.