Performing Precise, Seamless Hydrographic Surveys over Extended Areas Through Use of Integrated DGPS Reference Networks

L. Harold Spradley

Abstract:	Hydrographic surveys across broad geographical areas are a challenge to the differential GPS (DGPS) user: reference stations for computation and broadcast of differential data may be spaced hundreds of kilometers apart, such that their correction signals create 'jumps", or discontinuities of several meters at coverage boundaries between different reference stations. The paper analyzes several sources of error, ties, including base station control off-line-of-sight components of broadcast ephemeris data, varying components of refraction, and multi-path interference at base stations. For the past four years, GPS Technology Corp. has performed surveys over extended geographical regions wherein moving GPS antennas have been tracked and computed with . respect to wethree DGPS refiereDc.e stm at all times. The company's Multi-Base software and methodology provides verified accuracies of 0.5 meters for base station separations of 200 kilometers, 1.0 meters or better for base station networks of 500-kilometer spacing. These accuracies include transitions across boundaries in which different sets of stations are employed in the computation. Although the accuracy levels offered by Multi-Base are important to the user, one of the most significant benefits is that of having a continuous figure of merit, or accuracy audit, in the position(s) developed from the multiple, independent base station corrections. Since implementation of these methods in 1988, the company has surveyed more than 30,000 points in "rapid static" mode, and in dynamic mode these operations have covered more than 7400 line-miles of survey with more than 870,000 points of event computation. In more than half of these surveys, dual-antenna GPS operations have also provided pitch and azimuth information.
Published in:	Proceedings of the 1993 National Technical Meeting of The Institute of Navigation January 20 - 22, 1993 Parc 55 Hotel San Francisco, CA
Pages:	233 - 240
Cite this article:	Spradley, L. Harold, "Performing Precise, Seamless Hydrographic Surveys over Extended Areas Through Use of Integrated DGPS Reference Networks," Proceedings of the 1993 National Technical Meeting of The Institute of Navigation, San Francisco, CA, January 1993, pp. 233-240.
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