Results of GPS reprocessing campaign (1996-2011) provided by Geodetic observatory Pecný

The paper presents the GOP first reprocessing results, which officially contributed to the EPN-repro1 project. It also describes the 15-year GOP cumulative solution providing station coordinates, velocities and their discontinuities over the period of 1996-2011. Repeatabilities estimated from cleaned long-term coordinate time-series reached 1-2 mm and 4-6 mm in horizontal and vertical component, respectively. We then showed the exploitation of GOP reprocessing results in the assessment of the EUREF ITRF2005 densification and the latest ITRS realization, ITRF2008. We identified and confirmed the North-South tilt (≈ 2mas) in the currently available European reference frame based on the EPN cumulative solution updated in GPS week 1600. The study showed a historical development of the tilt and its close relation to a weak velocity datum definition of this realization, which is very important for a long-term datum prediction. Selected EPN station coordinates, velocities and discontinuities of the latest ITRS realization (ITRF2008) were also assessed. Specific problems for some EPN stations were identified in the global reference frame. This emphasized further necessity to check all the stations before their use for datum definition for regional densifications

Analysis of the time series of station coordinates - a comparison of the network and PPP approach

Based on the example of fourteen selected permanent GNSS stations of the EPN (EUREF Permanent Network) the differences of time variations of coordinates – velocities – resulting from the network and PPP (Precise Point Positioning) solution are studied. In both approaches the coordinates are determinated using the Bernese software version 5.2. The time series analysis is made using the modified Vaníček´s method. The comparison shows that the results provided by the two methods cannot be accepted as statistically consistent.Web of Science12213312

Estimating the impact of Global Navigation Satellite System horizontal delay gradients in variational data assimilation

We developed operators to assimilate Global Navigation Satellite System (GNSS) Zenith Total Delays (ZTDs) and horizontal delay gradients into a numerical weather model. In this study we experiment with refractivity fields derived from the Global Forecast System (GFS) available with a horizontal resolution of 0.5 degrees. We begin our investigations with simulated observations. In essence, we extract the tropospheric parameters from the GFS analysis, add noise to mimic observation errors and assimilate the simulated observations into the GFS 24h forecast valid at the same time. We consider three scenarios: (1) the assimilation of ZTDs (2) the assimilation of horizontal delay gradients and (3) the assimilation of both ZTDs and horizontal delay gradients. The impact is measured by utilizing the refractivity fields. We find that the assimilation of the horizontal delay gradients in addition to the ZTDs improves the refractivity field around 800 hPa. When we consider a single station there is a clear improvement when horizontal delay gradients are assimilated in addition to the ZTDs because the horizontal delay gradients contain information that is not contained in the ZTDs. On the other hand, when we consider a dense station network there is not a significant improvement when horizontal delay gradients are assimilated in addition to the ZTDs because the horizontal delay gradients do not contain information that is not already contained in the ZTDs. Finally, we replace simulated by real observations, that is, tropospheric parameters from a Precise Point Positioning solution provided with the G-Nut/Tefnut software, in order to show that the GFS 24h forecast is indeed improved when GNSS horizontal delay gradients are assimilated in addition to GNSS ZTDs; for the considered station (Potsdam, Germany) and period (June and July, 2017) we find an improvement in the retrieved refractivity of up to 4%.Web of Science111art. no. 4

Inter-technique validation of tropospheric slant total delays

An extensive validation of line-of-sight tropospheric slant total delays (STD) from Global Navigation Satellite Systems (GNSS), ray tracing in numerical weather prediction model (NWM) fields and microwave water vapour radiometer (WVR) is presented. Ten GNSS reference stations, including collocated sites, and almost 2 months of data from 2013, including severe weather events were used for comparison. Seven institutions delivered their STDs based on GNSS observations processed using 5 software programs and 11 strategies enabling to compare rather different solutions and to assess the impact of several aspects of the processing strategy. STDs from NWM ray tracing came from three institutions using three different NWMs and ray-tracing software. Inter-techniques evaluations demonstrated a good mutual agreement of various GNSS STD solutions compared to NWM and WVR STDs. The mean bias among GNSS solutions not considering post-fit residuals in STDs was -0.6 mm for STDs scaled in the zenith direction and the mean standard deviation was 3.7 mm. Standard deviations of comparisons between GNSS and NWM ray-tracing solutions were typically 10 mm +/- 2 mm (scaled in the zenith direction), depending on the NWM model and the GNSS station. Comparing GNSS versus WVR STDs reached standard deviations of 12 mm +/- 2 mm also scaled in the zenith direction. Impacts of raw GNSS post-fit residuals and cleaned residuals on optimal reconstructing of GNSS STDs were evaluated at intertechnique comparison and for GNSS at collocated sites. The use of raw post-fit residuals is not generally recommended as they might contain strong systematic effects, as demonstrated in the case of station LDB0. Simplified STDs reconstructed only from estimated GNSS tropospheric parameters, i.e. without applying post-fit residuals, performed the best in all the comparisons; however, it obviously missed part of tropospheric signals due to non-linear temporal and spatial variations in the troposphere. Although the post-fit residuals cleaned of visible systematic errors generally showed a slightly worse performance, they contained significant tropospheric signal on top of the simplified model. They are thus recommended for the reconstruction of STDs, particularly during high variability in the troposphere. Cleaned residuals also showed a stable performance during ordinary days while containing promising information about the troposphere at low-elevation angles.Web of Science1062208218

Sensitivity of GNSS tropospheric gradients to processing options

An analysis of processing settings impacts on estimated tropospheric gradients is presented. The study is based on the benchmark data set collected within the COST GNSS4SWEC action with observations from 430 Global Navigation Satellite Systems (GNSS) reference stations in central Europe for May and June 2013. Tropospheric gradients were estimated in eight different variants of GNSS data processing using precise point positioning (PPP) with the G-Nut/Tefnut software. The impacts of the gradient mapping function, elevation cut-off angle, GNSS constellation, observation elevation-dependent weighting and real-time versus post-processing mode were assessed by comparing the variants by each to other and by evaluating them with respect to tropospheric gradients derived from two numerical weather models (NWMs). Tropospheric gradients estimated in post-processing GNSS solutions using final products were in good agreement with NWM outputs. The quality of high-resolution gradients estimated in (near-)real-time PPP analysis still remains a challenging task due to the quality of the real-time orbit and clock corrections. Comparisons of GNSS and NWM gradients suggest the 3 degrees elevation angle cut-off and GPS+GLONASS constellation for obtaining optimal gradient estimates provided precise models for antenna-phase centre offsets and variations, and tropospheric mapping functions are applied for low-elevation observations. Finally, systematic errors can affect the gradient components solely due to the use of different gradient mapping functions, and still depending on observation elevation-dependent weighting. A latitudinal tilting of the troposphere in a global scale causes a systematic difference of up to 0.3 mm in the north-gradient component, while large local gradients, usually pointing in a direction of increasing humidity, can cause differences of up to 1.0 mm (or even more in extreme cases) in any component depending on the actual direction of the gradient. Although the Bar-Sever gradient mapping function provided slightly better results in some aspects, it is not possible to give any strong recommendation on the gradient mapping function selection.Web of Science37344642

Results of GPS reprocessing campaign (1996-2011) provided by Geodetic observatory Pecný

The paper presents the GOP first reprocessing results, which officially contributed to the EPN-repro1 project. It also describes the 15-year GOP cumulative solution providing station coordinates, velocities and their discontinuities over the period of 1996-2011. Repeatabilities estimated from cleaned long-term coordinate time-series reached 1-2 mm and 4-6 mm in horizontal and vertical component, respectively. We then showed the exploitation of GOP reprocessing results in the assessment of the EUREF ITRF2005 densification and the latest ITRS realization, ITRF2008. We identified and confirmed the North-South tilt (≈ 2mas) in the currently available European reference frame based on the EPN cumulative solution updated in GPS week 1600. The study showed a historical development of the tilt and its close relation to a weak velocity datum definition of this realization, which is very important for a long-term datum prediction. Selected EPN station coordinates, velocities and discontinuities of the latest ITRS realization (ITRF2008) were also assessed. Specific problems for some EPN stations were identified in the global reference frame. This emphasized further necessity to check all the stations before their use for datum definition for regional densifications

Results of GPS reprocessing campaign (1996-2011) provided by Geodetic observatory Pecný

The paper presents the GOP first reprocessing results, which officially contributed to the EPN-repro1 project. It also describes the 15-year GOP cumulative solution providing station coordinates, velocities and their discontinuities over the period of 1996-2011. Repeatabilities estimated from cleaned long-term coordinate time-series reached 1-2 mm and 4-6 mm in horizontal and vertical component, respectively. We then showed the exploitation of GOP reprocessing results in the assessment of the EUREF ITRF2005 densification and the latest ITRS realization, ITRF2008. We identified and confirmed the North-South tilt (≈ 2mas) in the currently available European reference frame based on the EPN cumulative solution updated in GPS week 1600. The study showed a historical development of the tilt and its close relation to a weak velocity datum definition of this realization, which is very important for a long-term datum prediction. Selected EPN station coordinates, velocities and discontinuities of the latest ITRS realization (ITRF2008) were also assessed. Specific problems for some EPN stations were identified in the global reference frame. This emphasized further necessity to check all the stations before their use for datum definition for regional densifications