Acta Geodynamica et Geomaterialia

Title: UNCERTAINTIES OF GEODETIC VELOCITIES FROM PERMANENT GPS OBSERVATIONS:THE SUDETEN CASE STUDY
Authors: Klos Anna, Bogusz Janusz, Figurski Mariusz and Kosek Wieslaw
DOI: 10.13168/AGG.2014.0005
Journal: Acta Geodynamica et Geomaterialia, Vol. 11, No. 3 (175), Prague 2014
Full Text: PDF file (1.3 MB)
Keywords: GPS, noises, ASG-EUPOS, Sudeten area, MLE
Abstract: The assumption that the GPS-derived coordinate time series behave like the white noise leads to the underestimation of the velocity uncertainties. The permanent stations velocities are required nowadays with the stability at the level of 0.1 mm/year in case of using them to the kinematic reference frame realization or numerous geodynamic interpretations. Therefore, it is required to know which kind of noise models exists in the time series of geodetic coordinates changes. These noises can be the effect of e.g. mismodelled satellite orbits or improperly mounted antennae. In the following paper, three combinations of noise models were assumed in the GPS time series: the white noise model only, to show how the omitting of correlations in the stochastic part of the GPS time series underestimates the velocity uncertainties; the combination of the white plus flicker plus random-walk noise to estimate which of the power-law noises with the known spectral index prevails in the GPS time series; and the combination of the white plus power-law noise to estimate which coloured noise fits the stochastic part the best. We analyzed more than 40 stations (belonging to the ASG-EUPOS and EPN networks) with 5 years of observations from the area of Sudeten. The results show that the amplitudes of the white noise for the assumption of white noise only model range from 0.6 to 2 mm for the horizontal (North and East) components and from 2 to 8 mm for the vertical (Up) component, while the velocity uncertainties range from 0.01 to 0.13 mm/year for the horizontal velocities and from 0.04 to 0.24 for the vertical one. For the combination of the white, flicker and random-walk noise, the white noise is at the same level in the entire analyzed area, while the flicker noise prevails over other kinds of noise for all components. For the North and East its amplitude ranges from 2 to 5 mmyr-0.25, while for the U component it is 2-3 times larger. Here, the uncertainty of permanent stations velocity ranges from 0.1 mm/year for the horizontal components to even 1.1 mm/year for the vertical one, which is over 10 times larger than the assumed level of stability of permanent stations velocity. For the last combination, the obtained spectral indices range from -1.6 to -0.4 for the horizontal components and from -1.0 to -0.4 for the vertical component, which confirms the prevalence of fractional white and Brownian motion quite close to flicker noise with amplitudes of power-law noise of 2-5 mmyrκ/4 and 4-12 mm*yrκ/4, respectively. For this combination, the errors of the estimated velocities reach in the most extreme case even 0.8 mm/year for the Up component, which is 8 times greater than the required stability level.