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See detailAn Evaluaton of Real-Time Troposphere Products Based on mult-GNSS Precise Point Posi)oning
Ding, Wenwu; Teferle, Felix Norman UL; Kazmierski, Kamil et al

Scientific Conference (2017, February 21)

When employing observations from multiple Global Navigation Satellite System (GNSS) the performance of real-time (RT) GNSS meteorology can be improved. In this paper, we describe an operational RT system ... [more ▼]

When employing observations from multiple Global Navigation Satellite System (GNSS) the performance of real-time (RT) GNSS meteorology can be improved. In this paper, we describe an operational RT system for extracting zenith tropospheric delay (ZTD) using a modified version of the PPP-wizard. Multi-GNSS, including GPS, GLONASS and Galileo, observation streams are processed using a RT PPP strategy based on RT satellite orbit/clock products from CNES. A continuous experiment for 30 days is conducted, in which the RT observation streams of 20 globally distributed stations are processed. The initialization time and accuracy of the RT troposphere products using single/multi-system observations are evaluated. The effect of RT PPP ambiguity resolution is also evaluated. The results reveal that the RT troposphere products based on single system observations can fulfill the requirements of meteorological application, in which the GPS-only solution is better than the GLONASS-only solution in both initialization and accuracy. The performance can also be improved by applying RT PPP ambiguity resolution and utilizing multi-GNSS observations. Specifically, we notice that the ambiguity resolution is more effective in improving the accuracy, whereas the initialization process can be better accelerated by multi-GNSS observations. Combining all systems, RT troposphere products with an average accuracy of about 8 mm in ZTD can be achieved after an initialization process of approximately 9 minutes, which supports the application of multi-GNSS observations and ambiguity resolution for RT meteorological applications. [less ▲]

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See detailAn evaluation of real-time troposphere estimation based on GNSS Precise Point Positioning
Ding, Wenwu; Teferle, Felix Norman UL; Kazmierski, Kamil et al

in Journal of Geophysical Research: Atmospheres (2017), 122(5), 2779--2790

It is anticipated that the performance of real-time (RT) GNSS meteorology can be further improved by incorporating observations from multiple Global Navigation Satellite System (GNSS), including GPS ... [more ▼]

It is anticipated that the performance of real-time (RT) GNSS meteorology can be further improved by incorporating observations from multiple Global Navigation Satellite System (GNSS), including GPS, GLONASS, Galileo, and BeiDou. In this paper, an operational RT system for extracting zenith troposphere delay (ZTD) using a modified version of the Precise Point Positioning With Integer and Zero-difference Ambiguity Resolution Demonstrator (PPP-WIZARD) was established. GNSS, including GPS, GLONASS, and Galileo, observation streams were processed using RT Precise Point Positioning (PPP) strategy based on RT satellite orbit/clock products from the Centre National d'Etudes Spatiales. An experiment covering 30 days was conducted, in which the observation streams of 20 globally distributed stations were processed. The initialization time and accuracy of the RT troposphere results using single-system and multisystem observations were evaluated. The effect of PPP ambiguity resolution was also evaluated. Results reveal that RT troposphere estimates based on single-system observations can both be applied in weather nowcasting, in which the GPS-only solution is better than the GLONASS-only solution. The performance can also be improved by PPP ambiguity resolution and utilizing GNSS observations. Specifically, we notice that ambiguity resolution is more effective in improving the accuracy of ZTD, whereas the initialization process can be better accelerated by GNSS observations. Combining all techniques, the RT troposphere results with an average accuracy of about 8 mm in ZTD can be achieved after an initialization process of approximately 8.5 min, which demonstrates superior results for applying GNSS observations and ambiguity resolution for RT meteorological applications. [less ▲]

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See detailMulti-GNSS Benefits to Real-Time and Long-Term Monitoring Applications
Teferle, Felix Norman UL; Ding, Wenwu; Abraha, Kibrom Ebuy UL et al

Scientific Conference (2016, July 30)

The processing of observations from multiple Global Navigation Satellite Systems (GNSSs) has been shown to benefit high-precision applications on time scales from real-time (RT) to long-term monitoring ... [more ▼]

The processing of observations from multiple Global Navigation Satellite Systems (GNSSs) has been shown to benefit high-precision applications on time scales from real-time (RT) to long-term monitoring. While the improvements for RT applications have been widely documented and stem largely from the availability of additional observations, often with better satellite geometry, especially in obstructed environments, the improvements to long-term monitoring applications are less well understood. In this evaluation two distinct examples from recent studies carried out at the University of Luxembourg will be presented. Firstly, we will discuss RT estimates of Zenith Tropospheric Delay (ZTD) obtained using integer ambiguity fixed Precise Point Positioning (PPP) solutions based on GPS, GLONASS, Galileo and BDS observations. This study revealed that the largest improvement in the ZTD estimates stemmed from the additional GNSS observations to those of GPS. The fixing of integer ambiguities (GPS only) had less of an effect. Secondly, we will discuss long-term PPP solutions using GPS and GLONASS observations in combination with various satellite orbit and clock products from the International GNSS Service and its analysis centres. Here of particular interest are the constellation specific draconitic signals and the impact of signal obstructions on the long-term position time series. [less ▲]

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See detailComparative analysis of different environmental loading methods and their impacts on the GPS height time series
Jiang, Weiping; Li, Zhao UL; van Dam, Tonie UL et al

in Journal of Geodesy (2013), 87(7), 687-703

Three different environmental loading methods are used to estimate surface displacements and correct nonlinear variations in a set of GPS weekly height time series. Loading data are provided by (1) Global ... [more ▼]

Three different environmental loading methods are used to estimate surface displacements and correct nonlinear variations in a set of GPS weekly height time series. Loading data are provided by (1) Global Geophysical Fluid Center (GGFC), (2) Loading Model of Quasi-Observation CombinationAnalysis software (QLM) and (3) our own daily loading time series (we call itOMDfor optimum model data). We find that OMD has the smallest scatter in height across the selected 233 globally distributed GPS reference stations, GGFC has the next smallest variability, and QLM has the largest scatter. By removing the load-induced height changes from the GPS height time series, we are able to reduce the scatter on 74, 64 and 41 % of the stations using the OMD models, the GGFC model and QLM model respectively. We demonstrate that the discrepancy between the center of earth (CE) and the center of figure (CF) reference frames can be ignored. The most important differences between the predicted models are caused by (1) differences in the hydrol- ogy data from the National Center for Atmospheric Research (NCEP) vs. those from the Global Land Data Assimilation System (GLDAS), (2) grid interpolation, and (3) whether the topographic effect is removed or not. Both QLM and GGFC are extremely convenient tools for non-specialists to use to calculate loading effects. Due to the limitation ofNCEP reanalysis hydrology data compared with theGLDAS model, theGGFCdataset is much more suitable thanQLMfor applying environmental loading corrections to GPS height time series. However, loading results for Greenland from GGFC should be discarded since hydrology data from GLDAS in this region are not accurate. The QLM model is equivalent to OMD in Greenland and, hence, could be used as a complement to the GGFC product to model the load in this region. We find that the predicted loading from all three models cannot reduce the scatter of the height coordinate for some stations in Europe. [less ▲]

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