Browse by author
Lookup NU author(s): Professor Geoffrey Blewitt, Dr David Lavallee
Full text for this publication is not currently held within this repository. Alternative links are provided below where available.
Our analysis of Global Positioning System (GPS) site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal, and 4 mm for vertical, with some sites at twice these amplitudes. Power spectrum analysis confirms that GPS time series also contain significant power at annual harmonic frequencies (with spectral indices ), which indicates the presence of repeating signals. Van Dam et al. [2001] showed that a major annual component is induced by hydrological and atmospheric loading. Unless accounted for, we show that annual signals can significantly bias estimation of site velocities intended for high accuracy purposes such as plate tectonics and reference frames. For such applications, annual and semi-annual sinusoidal signals should be estimated simultaneously with site velocity and initial position. We have developed a model to calculate the level of bias in published velocities that do not account for annual signals. Simultaneous estimation might not be necessary beyond 4.5 years, as the velocity bias rapidly becomes negligible. Minimum velocity bias is theoretically predicted at integer-plus-half years, as confirmed by tests with real data. Below 2.5 years, the velocity bias can become unacceptably large, and simultaneous estimation does not necessarily improve velocity estimates, which rapidly become unstable due to correlated parameters. We recommend that 2.5 years be adopted as a standard minimum data span for velocity solutions intended for tectonic interpretation or reference frame production, and that we be skeptical of geophysical interpretations of velocities derived using shorter data spans.
Author(s): Blewitt G, Lavallée DA
Publication type: Article
Publication status: Published
Journal: Journal of Geophysical Research
Year: 2001
Volume: 107
Issue: B7
ISSN (print): 0148-0227
ISSN (electronic): 1934-8843
Publisher: American Geophysical Union
URL: http://dx.doi.org/10.1029/2001JB000570
DOI: 10.1029/2001JB000570
Altmetrics provided by Altmetric
