GPS-based Measurement of Atmospheric Tides

Todd E. Humphreys, Michael C. Kelley, Paul M. Kintner Jr.

Abstract:	Frequency analyses of Zenith Neutral Delay estimates provided by ground-based GPS receivers show peaks at frequencies corresponding to the lunar day, the solar day, and subharmonics of the solar day. The origins of these peaks are investigated. A significant component of the peak at the lunar semidiurnal period is shown to be artifactual. Its amplitude has attenuated markedly since 1997 as the models used to calculate Zenith Neutral Delay have been refined. On the other hand, the data suggest that the solar diurnal and semidiurnal oscillations are physical, originating in the S1 and S2 atmospheric tides. A comparison between Zenith Neutral Delay and surface pressure measurements of the S2 tide reveals a close agreement in the global distribution and in the zonal wave components measured by the two methods. This is true to a lesser degree for the S1 tide, presumably because its greater spatial irregularity is not resolved well by the widely spaced GPS receivers used in this study. A technique exploiting closely located GPS receivers with large altitude differences reveals that the peaks at the solar tidal frequencies are probably not due to orbit modeling errors, solid earth tide modeling errors, earth orientation parameter errors, or other errors that would be common to the two sites. The origins of the peaks at subharmonics of the solar day, with periods of 8, 6, 4.8 and 4 hours, are less understood. Similar oscillations have recently been discovered in very long baseline interferometry measurements of earth orientation parameters, suggesting that these oscillations are also physical. The GPS-based method for studying atmospheric tides offers an instantaneous measure of the atmospheric density integrated over the path of the GPS signal, thereby providing information on tidal features above the surface of the Earth. The method also enjoys a large network of existing GPS stations and time resolution down to 5 min.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	864 - 880
Cite this article:	Humphreys, Todd E., Kelley, Michael C., Kintner, Paul M., Jr., "GPS-based Measurement of Atmospheric Tides," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 864-880.
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