Determining Earth Orientation by Global Positioning System at the US Naval Observatory

Peter Kammeyer and James Rhode

Abstract:	The U.S. Naval Observatory determines the orientation of the Earth from its observations of distant celestial radio sources, also including in this determination other sources of data. Because of the expense of the radio observations, the Observatory would like, if possible, to reduce the required observing time. To maintain accurate knowledge of Earth orientation between observations in a reduced schedule, the Observatory desires to use analysis of observations of GPS satellites. The Observatory’s effort to analyze GPS satellite orbits is directed toward the determination of both polar motion and UTl, the rotation angle of the Earth around its axis. This effort uses a combination of the JPL GIPSY software and additional software developed at the Observatory. Determination of polar motion by analysis of GPS orbits began on a trial basis at the Observatory in late 1994. This paper will report the results obtained for polar motion parameters and give the results of an experiment determining UT1 from length-of-day values found in GPS analysis. The Observatory’s effort to determine UT1 has further led to determination of a mean rate for that part of the motion of the orbit pole, the unit vector normal to the orbit, coming from once-per-revolution terms in radiation pressure acceleration with the effect of varying distance from the sun removed. This additional mean rate depends on the position of the Sun relative to the orbit plane, and that dependence remains nearly the same from year to year. We have thus concluded that it will be possible to obtain UT1 , between calibrations by VLBI every two weeks, with an rms error less than 0.2 millisecond.
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:	73 - 81
Cite this article:	Kammeyer, Peter, Rhode, James, "Determining Earth Orientation by Global Positioning System at the US Naval Observatory," 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. 73-81.
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