Noise Analysis of Continuous GPS Time Series of Selected EPN Stations to Investigate Variations in Stability of Monument Types

Abstract

The type of monument that a GPS antenna is placed on plays a significant role in noise estimation for each permanent GPS station. In this research 18 Polish permanent GPS stations that belong to the EPN (EUREF Permanent Network) were analyzed using Maximum Likelihood Estimation (MLE). The antennae of Polish EPN stations are placed on roofs of buildings or on concrete pillars. The analyzed data covers a period of 5 years from 2008 to 2013. The analysis was made on the daily topocentric coordinate changes. Firstly, the existence of the combination of white noise, flicker noise and random-walk on each of the stations was set up before the analysis, secondly – a random-walk plus white noise model was assumed, because monument instability is thought to follow random-walk. The first combination of noises did not yield any conclusions about stability of monuments, probably because of the domination of flicker noise in the time series. The second one, even if not quite correct – noises in GPS time series do not strictly reflect random-walk only-showed that concrete pillars perform better than buildings for GPS antenna locations. Unfortunately, on the basis of this it cannot be clearly stated whether they are better as monuments or not. Moreover, the stacked Power Spectral Densities (PSDs) of topocentric coordinates were obtained with Fast Fourier Transform (FFT) for each monument type. Even though stacked spectra are quite similar and do not really show any differences, PSDs made for certain station are more varied.