A Compact Earth Tides Algorithm for WADGPS

James Sinko

Abstract:	This paper presents an algorithm for calculating the cyclic displacements of geo-features and locations due to solid earth tides. Wide-area differential GPS (WADGPS) systems designed for accuracies of better than 2 m need to account for tidal effects on the solid earth which can result in coordinate displacements of as much as 45 cm in the vertical direction. Differential position changes as large as 30 cm can occur between stations 3000 km apart. The algorithm presented is about 50 lines long. This short length is obtained by solving the tidal potential directly rather than by using the traditional harmonic analysis. (The harmonic analysis, while useful for tidal measurements, is not needed for predictions). Since no harmonics are left out, the accuracy of the model is better than 2 cm. The model predicts both radial and horizontal displacements (radial displacements are the dominant effect). The algorithm has been incorporated into Exploitation of Differential GPS for Guidance Enhancement (EDGE), a militarized WADGPS system employed during a recent (June 1995) demonstration on DGPS for precision munition delivery at Eglin Air Force Base, FL. This DGPS network is giving submeter accuracies at locations that are more than 1000 km from the nearest reference receiver.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	35 - 44
Cite this article:	Sinko, James, "A Compact Earth Tides Algorithm for WADGPS," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 35-44.
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