Investigation of Annual Variations in the WCDA GPS Solutions

Xin Chen, Richard B. Langley and Herb Dragert

Abstract:	Data from the Western Canada Deformation Array (WCDA), a network of continuous GPS tracking sites located in southwestern British Columbia, have been routinely processed since September 1992. Previous analyses of the WCDA solutions revealed unexplained annual sinusoidal variations in the north component of the three longest-running baselines with amplitudes ranging from 2.1 to 3.4 mm. These variations seem to be correlated with the orientation of the baselines and not the baseline lengths. Precise orbits, which are held fixed in the routine WCDA data reduction, were suspected as the cause in previous reports, though this was not fully proven. Recently, six tests have been carried out in an effort to identify the true cause of these annual variations. From the results of these tests, some factors, such as station-satellite geometry related errors and tropospheric mismodelling, can be discounted. The most interesting result from this study is that a similarity in features is found between the annual variations and an error caused by the uncalibrated GPS satellite antenna offset along the satellite local x-axis. This finding reinforces the suspicion of a systematic orbital error in the precise orbits, although common, site-specific, seasonal midulations of the GPS signal cannot be completely ruled out.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	1809 - 1818
Cite this article:	Chen, Xin, Langley, Richard B., Dragert, Herb, "Investigation of Annual Variations in the WCDA GPS Solutions," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 1809-1818.
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