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Abstract

Improvements in the analyses of Global Positioning System (GPS) observations yield
resolvable millimeter to submillimeter differences in coordinate estimates, thus providing
sufficient resolution to distinguish subtle differences in analysis methodologies. Here
we investigate the effects on site coordinates of using different approaches to modeling
atmospheric loading deformation (ATML) and handling of tropospheric delays. The
rigorous approach of using the time-varying Vienna Mapping Function 1 yields solutions
with lower noise at a range of frequencies compared with solutions generated using
empirical mapping functions. This is particularly evident when ATML is accounted for.
Some improvement also arises from using improved a priori zenith hydrostatic delays
(ZHD), with the combined effect being site-specific. Importantly, inadequacies in both
mapping functions and a priori ZHDs not only introduce time-correlated noise but
significant periodic terms at solar annual and semiannual periods. We find no significant
difference between solutions where nontidal ATML is applied at the observation level
rather than as a daily averaged value, but failing to model diurnal and semidiurnal tidal
ATML at the observation level can introduce anomalous propagated signals with periods
that closely match the GPS draconitic annual (351.4 days) and semiannual period
(175.7 days). Exacerbated by not fixing ambiguities, these signals are evident in both
stacked and single-site power spectra, with each tide contributing roughly equally to
the dominant semiannual peak. The amplitude of the propagated signal reaches a
maximum of 0.8 mm with a clear latitudinal dependence that is not correlated directly with
locations of maximum tidal amplitude.

Item Type:	Article
Authors/Creators:	Tregoning, P and Watson, CS
Journal or Publication Title:	Journal of Geophysical Research
ISSN:	0148-0227
DOI / ID Number:	https://doi.org/10.1029/2009JB006344
Additional Information:	Copyright 2009 by the American Geophysical Union.
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