Tropospheric products of the second GOP European GNSS reprocessing (1996–2014)

Abstract

Abstract. In this paper, we present results of the second reprocessing of all data from 1996 to 2014 from all stations in International Association of Geodesy (IAG) Reference Frame Sub-Commission for Europe (EUREF) Permanent Network (EPN) as performed at the Geodetic Observatory Pecný (GOP). While the original goal of this research was to ultimately contribute to the realization of a new European Terrestrial Reference System (ETRS), we also aim to provide a new set of GNSS (Global Navigation Satellite System) tropospheric parameter time series with possible applications to climate research. To achieve these goals, we improved a strategy to guarantee the continuity of these tropospheric parameters and we prepared several variants of troposphere modelling. We then assessed all solutions in terms of the repeatability of coordinates as an internal evaluation of applied models and strategies and in terms of zenith tropospheric delays (ZTDs) and horizontal gradients with those of the ERA-Interim numerical weather model (NWM) reanalysis. When compared to the GOP Repro1 (first EUREF reprocessing) solution, the results of the GOP Repro2 (second EU-REF reprocessing) yielded improvements of approximately 50 and 25 % in the repeatability of the horizontal and vertical components, respectively, and of approximately 9 % in tropospheric parameters. Vertical repeatability was reduced from 4.14 to 3.73 mm when using the VMF1 mapping function, a priori ZHD (zenith hydrostatic delay), and non-tidal atmospheric loading corrections from actual weather data. Raising the elevation cut-off angle from 3 to 7 • and then to 10 • increased RMS from coordinates' repeatability, which was then confirmed by independently comparing GNSS tropospheric parameters with the NWM reanalysis. The assessment of tropospheric horizontal gradients with respect to the ERA-Interim revealed a strong sensitivity of estimated gradients to the quality of GNSS antenna tracking performance. This impact was demonstrated at the Mallorca station, where gradients systematically grew up to 5 mm during the period between 2003 and 2008, before this behaviour disappeared when the antenna at the station was changed. The impact of processing variants on long-term ZTD trend estimates was assessed at 172 EUREF stations with time series longer than 10 years. The most significant site-specific impact was due to the non-tidal atmospheric loading followed by the impact of changing the elevation cut-off angle from 3 to 10 • . The other processing strategy had a very small or negligible impact on estimated trends.

Reduction of ZTD outliers through improved GNSS data processing and screening strategies

“…At this level of accuracy it is difficult to say which of ERAInterim or GPS is biased in an absolute sense. We note however, that the sign and magnitude of the bias are consistent with other studies (Dousa et al, 2017). The standard deviations of differences are about 10-11 mm, which is significantly larger than differences between GPS solutions (as also noticed in previous studies, e.g.…”

“…The standard deviations of differences are about 10-11 mm, which is significantly larger than differences between GPS solutions (as also noticed in previous studies, e.g. Dousa et al, 2017). The mean correlation 20 coefficients are about 0.975 for all three variants.…”

“…This screening option is however not to be used as it removes useful data. A better solution to the day boundary problem would be to combine solutions from successive days at the normal equation level (Dousa et al, 2017). The combination adjusts ZTD estimates across the 00:00 UTC boundaries for the central day and minimizes discontinuities between days.…”

Interpretation of the Tropospheric Gradients Estimated With GPS During Hurricane Harvey

“…However, as a consequence of the significant improvements in GPS processing algorithms, inconsistencies in long‐term time series have been introduced; therefore, there is a need for a homogeneous set of data for GPS meteorology. In this sense, the GPS community has contributed with reprocessed data that are useful for many applications (Dousa et al, ; Pacione & Di Tomaso, ).…”

“…Many studies have been developed and showed that horizontal gradients from ECMWF (European Centre for Medium‐Range Weather Forecasts) and water vapor radiometers (WVR) do agree with GPS‐estimated ones at the level of 0.5 mm for ECMWF and with a correlation of about 50% with WVR. See, for instance, Kačmařík et al (), Dousa et al (), Lu et al (), Li et al (), and Bar‐Sever et al (). Morel et al () have studied the behavior of the tropospheric gradients in Corsica island and have found that they can be influenced by both the slope of the relief and land/sea contrast in a mean year behavior.…”