Precise Pseudo-Kinematic GPS and Level Surveying to Obtain Gravity Deflections of the Vertical

Alan G. Evans, Benjamin W. Remondi

Abstract:	(NAVSWC) and the National Geodetic Survey (NGS) have jointly conducted testing to demonstrate the application of the Global Positioning System (GPS) pseudo-kinematic (PK) survey technique in combination with a first-order geodetic leveling survey for vertical deflection determination. The deflection of the vertical is the angular difference between a plumb line and a perpendicular to the Earth’s ellipsoid model and is used for precise inertial system alignment and navigation. These GPSlleveling derived values of vertical deflection are compared with values determined conventionally by both the U.S. Naval Observatory, using a Danjon astrolabe, and the Defense Mapping Agency, using a Wild T4 theodolite. The PK GPS survey used a single fixed receiver and four roving receivers that repeatedly collected data over a number of survey marks. The data processing was such that each baseline’s relative height value was determined from measurements of the same roving receiver antenna, which eliminates much of the antenna electric center bias. This procedure allows for very precise relative positioning. In addition, precise (0.1 arcsec) conventional values of vertical deflection and first-order (1.2 mm/km) leveling provide extremely accurate reference values over the 1-2-km baseline. The gravity vertical deflection measurements allow for the relative ellipsoid height estimates obtained from the PK GPS survey to be compared with the relative orthometric height obtained from the leveling survey. Here, a subcentimeter standard deviation of the relative height error and a mean error of about 1 mm were demonstrated. The objective of the PK technique is to efficiently and precisely obtain GPS baseline vectors for numerous short baselines in order to average down the effects of random errors. The aim of these tests is to demonstrate a cost effective alternative to traditional methods of obtaining vertical deflections. Test results for individual baselines and overall north and east components are presented.
Published in:	Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991) September 11 - 13, 1991 Albuquerque, NM
Pages:	681 - 690
Cite this article:	Evans, Alan G., Remondi, Benjamin W., "Precise Pseudo-Kinematic GPS and Level Surveying to Obtain Gravity Deflections of the Vertical," Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991), Albuquerque, NM, September 1991, pp. 681-690.
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