Atmospheric effects and spurious signals in GPS analyses

Abstract

[1] 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.

EPN-Repro2: A reference GNSS tropospheric data set over Europe

“…The conventional recommendation is to calculate the station displacement using the Ray and Ponte (2003) tidal model. However, crustal motion related to non-tidal atmospheric loading has been detected in station position time series from space geodetic techniques (van Dam et al, 1994;Mangiarotti et al, 2001;Tregoning and Van Dam, 2005). Several models of station displacements related to this effect are currently available.…”

“…To evaluate their impact, two solutions, one with and one without a non-tidal atmospheric loading model, have been compared for the year 2013. In the solution with the model, the National Centers for Environmental Prediction (NCEP) model is used at the observation level during data reduction (Tregoning and Watson, 2009). Dach et al (2010) have already found that the repeatability of the station coordinates improves by 20 % when applying the non-tidal atmospheric loading correction directly on the data analysis and by 10 % when applying a postprocessing correction to the resulting weekly coordinates.…”

The effect of using inconsistent ocean tidal loading models on GPS coordinate solutions

“…3). Other studies (Amiri-Simkooei et al 2007;Ray et al 2008;Tregoning and Watson 2009) have shown that the observed ∼annual and ∼semiannual peaks in power spectra of GPS timeseries are really GPS draconitic annual (∼351.4 days) and semiannual (∼175.7 days) periods. A GPS draconitic year is the period for the GPS constellation to repeat its orientation relative to the Sun (Ray et al 2008).…”

3-D GPS velocity field and its implications on the present-day post-orogenic deformation of the Western Alps and Pyrenees

“…Numerous sources of uncertainties affect GPS velocity estimations, especially in the vertical component: e.g., reference frame errors (Argus et al, 1999), seasonal signals (Blewitt and Lavallée, 2002), and atmospheric loading effects (Tregoning and Watson, 2009). These various sources of noise and non-tectonic signals can result in artificial trends over several years and systematic biases that may be correlated over large regions.…”