Abstract. The present availability of 18+ years of GNSS data belonging to the EUREF Permanent Network (EPN, http://www.epncb.oma.be/) is a valuable database for the development of a climate data record of GNSS tropospheric products over Europe. This data record can be used as a reference for a variety of scientific applications (e.g. validation of regional numerical weather prediction reanalyses and climate model simulations) and has a high potential for monitoring trends and the variability in atmospheric water vapour. In the framework of the EPN-Repro2, the second reprocessing campaign of the EPN, five Analysis Centres homogenously reprocessed the EPN network for the period 1996-2014. A huge effort has been made to provide solutions that are the basis for deriving new coordinates, velocities and tropospheric parameters for the entire EPN. The individual contributions are then combined to provide the official EPN reprocessed products. This paper is focused on the EPN-Repro2 tropospheric product. The combined product is described along with its evaluation against radiosonde data and European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-Interim) data.
Precise positioning using the signals of the Global Position System requires correcting the distance between the points of reception of the signal carrier phase and the antenna reference point. Sophisticated models to account for these phase errors are available and widely in use. These models are usually based on calibrations of several antennas of the same type to derive a mean model. There is also the possibility of applying individual correction models that are derived for one single antenna, since the individual antennas may still vary by a few millimeters. We prepared two sets of station position time series to understand the impact of using type mean or individual antenna correction models. At first, we estimated the station positions using the type mean model for the antenna corrections as it is provided by the IGS. Second, the same processing strategy was used, but this time with individual antenna correction models provided they were available. Then, based on these two solutions, we evaluated how different antenna corrections impact the network alignment and subsequently station coordinates. We showed that mixing two sources of antenna phase center corrections may influence the reference frame realization. However, this impact is very small and can be reduced by an appropriate selection of reference stations. Finally, we demonstrated that for some antennas, the application of type mean or individual antenna calibration models may cause a discrepancy in the position of over 10 mm for the horizontal and vertical component. However, for most of the antennas these offsets are below 2 mm for horizontal components and below 4 mm for vertical component. Thereby, for common antennas we confirmed the results obtained by others.
Abstract. The main purpose of this research was to acquire information about consistency of ZTD (zenith total delay) linear trends and seasonal components between two consecutive GPS reprocessing campaigns. The analysis concerned two sets of the ZTD time series which were estimated during EUREF (Reference Frame Sub-Commission for Europe) EPN (Permanent Network) reprocessing campaigns according to 2008 and 2015 MUT AC (Military University of Technology Analysis Centre) scenarios. Firstly, Lomb-Scargle periodograms were generated for 57 EPN stations to obtain a characterisation of oscillations occurring in the ZTD time series. Then, the values of seasonal components and linear trends were estimated using the LSE (least squares estimation) approach. The Mann-Kendall trend test was also carried out to verify the presence of linear long-term ZTD changes. Finally, differences in seasonal signals and linear trends between these two data sets were investigated. All these analyses were conducted for the ZTD time series of two lengths: a shortened 16-year series and a full 18-year one. In the case of spectral analysis, amplitudes of the annual and semi-annual periods were almost exactly the same for both reprocessing campaigns. Exceptions were found for only a few stations and they did not exceed 1 mm. The estimated trends were also similar. However, for the reprocessing performed in 2008, the trends values were usually higher. In general, shortening of the analysed time period by 2 years resulted in a decrease of the linear trends values of about 0.07 mm yr −1 . This was confirmed by analyses based on two data sets.
Advanced processing of collected global navigation satellite systems (GNSS) observations allows for the estimation of zenith tropospheric delay (ZTD), which in turn can be converted to the integrated water vapour (IWV). The proper estimation of GNSS IWV can be affected by the adopted GNSS processing strategy. To verify which of its elements cause deterioration and which improve the estimated GNSS IWV, we conducted eight reprocessings of 20 years of GPS observations (01.1996-12.2015). In each of them, we applied a different mapping function, the zenith hydrostatic delay (ZHD) a priori value, the cutoff angle, software, and the positioning method. Obtained in such a way, the ZTD time series were converted to the IWV using the meteorological parameters sourced from the ERA-Interim. Then, based on them, the long-term parameters were estimated and compared to those obtained from the IWV derived from the radio sounding (RS) observations. In this paper, we analyzed long-term parameters such as IWV mean values, linear trends, and amplitudes of annual and semiannual oscillations. A comparative analysis showed, inter alia, that in terms of the investigation of the IWV linear trend the precise point positioning (PPP) method is characterized by higher accuracy than the differential one. It was also found that using the GPT2 model and the higher elevation mask brings benefits to the GNSS IWV linear trend estimation.
The paper concerns investigation of the credibility of tectonic interpretation of GNSS strain rates. The analysis was focused on stable regions, where the crustal deformations are small and the reliability of GNSS velocities is questionable. We are showing how the unreliable motion of stations affects calculated strains around them. We expressed distribution of local principal strains by a sinusoidal function and used them to investigate the significance of strain distortion. Then we used this method to investigate real motions of GNSS stations. As a test object we used Polish GNSS stations belonging to the ASG-EUPOS network. Station velocities were estimated on the basis of the 4.5 years of observations. The results let us identify stations that disturb the obtained local GNSS strain rate field. After verification and exclusion of some stations, the new GNSS strains show a much greater internal compatibility and also better fit to the directions of lithosphere stresses.
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