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See detailA New Datum-Controlled Tide Gauge Record for Sea Level Studies in the South Atlantic Ocean: King Edward Point, South Georgia Island
Teferle, Felix Norman UL; Hunegnaw, Addisu UL; Woodworth, P. L. et al

Poster (2015, June 12)

In 2008 a new pressure tide gauge with Global Sea Level Observing System Number 187 was installed at King Edward Point (KEP), South Georgia Island, South Atlantic Ocean. This installation was carried out ... [more ▼]

In 2008 a new pressure tide gauge with Global Sea Level Observing System Number 187 was installed at King Edward Point (KEP), South Georgia Island, South Atlantic Ocean. This installation was carried out as part of the Antarctic Circumpolar Current Levels by Altimetry and Island Measurements (ACCLAIM) programme. In 2013 the KEP Geodetic Observatory was established in support of various scientific applications including the monitoring of vertical land movements at KEP. Currently, the observatory consists of two state-of-the-art Global Navigation Satellite System (GNSS) stations with local benchmark networks. In 2014 a tide board was added to the tide gauge, which, together with the measurements from the KEP Geodetic Observatory, now enables a calibration of the tide gauge. This will make it possible to include the KEP tide gauge in the Permanent Service for Mean Sea Level (PSMSL) database and make it available for future sea level studies. In this study, we will present the GNSS and levelling observations from the KEP Geodetic Observatory for the period from February 2013 to May 2015 used for the calibration of the tide gauge. While it is still too early to obtain accurate vertical land movement estimates from the GNSS data, the levelling campaigns in 2013 and 2014 indicated 7-9 mm of subsidence near the tide gauge. For the computation of the new height datum, geoid undulations derived from a seamless combination of the latest Gravity Observation Combination (GOCO) and Earth Gravitational Model (EGM) 2008 models were used. The use of this combined gravity model introduced a datum shift of approximately -24 cm compared to the previous datum. [less ▲]

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See detailSofia University GNSS Analysis Center (SUGAC)
Simeonov, Tzvetan; Sidorov, Dmitry UL; Teferle, Felix Norman UL et al

Scientific Conference (2015, May 20)

The Sofia University GNSS Analysis Centre (SUGAC, suada.phys.uni-sofia.bg) is a new analysis centre established via collaboration between the Department of Meteorology and Geophysics of Sofia University ... [more ▼]

The Sofia University GNSS Analysis Centre (SUGAC, suada.phys.uni-sofia.bg) is a new analysis centre established via collaboration between the Department of Meteorology and Geophysics of Sofia University, the IPOS - BuliPOS GNSS network in Bulgaria, the University of Luxembourg and the Space Research and Technology Institute at the Bulgarian Academy of Sciences. In April 2014, the first processing campaign took place. One year of GNSS data from 7 stations of the BuliPOS network were processed in collaboration with the University of Luxembourg. Tropospheric products (Zenith Total Delay and gradients) with 5 min temporal resolution were obtained using the NAPEOS software, developed by ESA. The tropospheric products from this campaign were then used for validation of the Weather Research and Forecasting (WRF) model as well as for case studies during intense precipitation events and fog. In this work the WRF model validation for Bulgaria will be presented. Future work will be the establishment of autonomous near real- time processing of the regional ground-based GNSS network in Southeast Europe in support of the EUMETNET E-GVAP and COST ES1206 ”Advanced Global Navigation Satellite Systems for Severe Weather Events and Climate” projects. [less ▲]

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See detailA Multi-Year Combination of Tide Gauge Benchmark Monitoring (TIGA) Analysis Center Products
Hunegnaw, Addisu UL; Teferle, Felix Norman UL

Poster (2015, April 12)

In 2013 the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group (WG) started their reprocessing campaign, which proposes to re-analyze all relevant Global Positioning ... [more ▼]

In 2013 the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group (WG) started their reprocessing campaign, which proposes to re-analyze all relevant Global Positioning System (GPS) observations from 1994 to 2013. This re-processed dataset will provide high quality estimates of land motions, enabling regional and global high-precision geophysical/geodetic studies. Several of the individual TIGA Analysis Centres (TACs) have completed processing the full history of GPS observations recorded by the IGS global network, as well as, many other GPS stations at or close to tide gauges, which are available from the TIGA data centre at the University of La Rochelle (www.sonel.org). Following the recent improvements in processing models and strategies, this is the first complete reprocessing attempt by the TIGA WG to provide homogeneous position time series. We report a first multi-year weekly combined solutions from the TIGA Combination Centre (TCC) at the University of Luxembourg (UL) using two independent combination software packages: CATREF and GLOBK. These combinations allow an evaluation of any effects from the combination software and of the individual TAC parameters and their influences on the combined solution. Some major results of the UL TIGA multi-year combinations in terms of geocentric sea level changes will be presented and discussed. [less ▲]

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See detailCalibration of the Tide Gauge at King Edward Point, South Georgia Island
Teferle, Felix Norman UL; Hunegnaw, Addisu UL; Woodworth, P L et al

Poster (2015, March 12)

After initial sea level observations in the 1950s, a new pressure tide gauge (Global Sea Level Observing System 187) was installed at King Edward Point (KEP), South Georgia Island, British Overseas ... [more ▼]

After initial sea level observations in the 1950s, a new pressure tide gauge (Global Sea Level Observing System 187) was installed at King Edward Point (KEP), South Georgia Island, British Overseas Territories in the South Atlantic Ocean, in 2008. This was car-ried out as part of the ACCLAIM (Antarctic Circumpolar Current Levels by Altimetry and Island Measurements) programme. In 2013 the KEP Geodetic Observato-ry was established in support of various geoscience applications including the monitor-ing of vertical land movements at KEP. Currently, the observatory consists of two state-of-the-art GNSS stations with local benchmark networks, allowing the height determina-tions from the GNSS antennas to be transferred to the tide gauge and forming a height reference within the International Terrestrial Reference Frame. Finally in 2014, a tide board was added to the tide gauge, which, together with the GNSS and levelling obser-vations, now allows the calibration of the tide gauge. In this study, we will present the results from the calibration of the tide gauge using the GNSS observations from the KEP Geodetic Observatory for the period from February 2013 to present, the levelling campaigns in 2013 and 2014, and geoid undulations de-rived from a seamless combination of the latest GOCO and EGM2008 gravity models. [less ▲]

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See detailAssimilation of zenith total delays in the AROME France convective scale model: a recent assessment
Mahfouf, Jean-Francois; Ahmed, Furqan UL; Moll, Patrick et al

in Tellus : Series A (2015)

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See detailAssessment of BLT Tide Gauge Benchmark Monitoring (TIGA) repro2 solutions
Hunegnaw, Addisu UL; Teferle, Felix Norman UL

Poster (2015)

In 2013 the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group (WG) started their reprocessing campaign, which proposes to re-analyze all relevant Global Positioning ... [more ▼]

In 2013 the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group (WG) started their reprocessing campaign, which proposes to re-analyze all relevant Global Positioning System (GPS) observations from 1994 to 2013. This re-processed dataset will provide high quality estimates of land motions, enabling regional and global high-precision geophysical/geodetic studies. Several of the individual TIGA Analysis Centres (TACs) have completed processing the full history of GPS observations recorded by the IGS global network, as well as, many other GPS stations at or close to tide gauges, which are available from the TIGA data centre at the University of La Rochelle (www.sonel.org). Following the recent improvements in processing models and strategies, this is the first complete reprocessing attempt by the BLT TIGA Analysis centre to provide homogeneous position time series. We report the quality of the multi-year daily solutions from the consortium of the British Isles continuous GNSS Facility (BIGF) and the University of Luxembourg TIGA Analysis Centres (BLT) based on the Bernese GNSS Software Version 5.2 using a double difference (DD) network processing strategy. [less ▲]

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See detailComparative Analysis of Real-Time Precise Point Positioning Zenith Total Delay Estimates
Ahmed, Furqan UL; Vaclavovic, Pavel; Teferle, Felix Norman UL et al

in GPS Solutions (2014)

The continuous evolution of global navigation satellite systems (GNSS) meteorology has led to an increased use of associated observations for operational modern low-latency numerical weather prediction ... [more ▼]

The continuous evolution of global navigation satellite systems (GNSS) meteorology has led to an increased use of associated observations for operational modern low-latency numerical weather prediction (NWP) models, which assimilate GNSS-derived zenith total delay (ZTD) estimates. The development of NWP models with faster assimilation cycles, e.g., 1-h assimilation cycle in the rapid update cycle NWP model, has increased the interest of the meteorological community toward sub-hour ZTD estimates. The suitability of real-time ZTD estimates obtained from three different precise point positioning software packages has been assessed by comparing them with the state-of-the-art IGS final troposphere product as well as collocated radiosonde (RS) observations. The ZTD estimates obtained by BNC2.7 show a mean bias of 0.21 cm, and those obtained by the G-Nut/Tefnut software library show a mean bias of 1.09 cm to the IGS final troposphere product. In comparison with the RS-based ZTD, the BNC2.7 solutions show mean biases between 1 and 2 cm, whereas the G-Nut/Tefnut solutions show mean biases between 2 and 3 cm with the RS-based ZTD, and the ambiguity float and ambiguity fixed solutions obtained by PPPWizard have mean biases between 6 and 7 cm with the references. The large biases in the time series from PPP-Wizard are due to the fact that this software has been developed for kinematic applications and hence does not apply receiver antenna eccentricity and phase center offset (PCO) corrections on the observations. Application of the eccentricity and PCO corrections to the a priori coordinates has resulted in a 66 % reduction of bias in the PPP-Wizard solutions. The biases are found to be stable over the whole period of the comparison, which are criteria (rather than the magnitude of the bias) for the suitability of ZTD estimates for use in NWP nowcasting. A millimeter-level impact on the ZTD estimates has also been observed in relation to ambiguity resolution. As a result of a comparison with the established user requirements for NWP nowcasting, it was found that both the GNut/Tefnut solutions and one of the BNC2.7 solutions meet the threshold requirements, whereas one of the BNC2.7 solution and both the PPPWizard solutions currently exceed this threshold. [less ▲]

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See detailImpact of Station GNSS Antenna Phase Centre Calibrations on Satellite Orbits and Station Coordinates: Preliminary Results
Sidorov, Dmitry UL; Teferle, Felix Norman UL

Poster (2014, October 14)

The electromagnetic phase centre of a Global Navigation Satellite System (GNSS) antenna does not coincide with the physical one and depends on the azimuth and elevation of the incoming signals. To improve ... [more ▼]

The electromagnetic phase centre of a Global Navigation Satellite System (GNSS) antenna does not coincide with the physical one and depends on the azimuth and elevation of the incoming signals. To improve processing results, the International GNSS Service has developed antenna phase centre corrections (PCC), which include models for constant and variable biases, i.e. phase centre offsets and phase centre variations. By assuming that the small differences in PCCs between antenna/radome combinations of the same type/model are negligible, so called type-mean PCCs have been generated and, for practical reasons, have been widely applied. The type-mean PCCs are averaged corrections, which are composed from several individual PCCs. Contrary to the general assumption, individual PCCs may sometimes be significantly different for antennas of the same type and it can be argued, that the use of type-mean instead of individual calibrations may degrade GNSS-derived products, such as satellite orbits and station coordinates. Furthermore, through simple geometric considerations it can be shown that inaccuracies in the PCCs may propagate into time series of GNSS solutions and may contribute some power at the orbital frequencies and their harmonics. In this study we assess the impact of the applied antenna PCCs on satellite orbits and station coordinates. As the availability of individual PCCs for GNSS stations is very limited, we analyzed a global network with stations mainly located in Europe. We used 10 years of GPS data in our processing. Despite the limitations imposed by the poor network geometry, we observed improvements in orbit overlaps at day boundaries when individual antenna PCCs were used compared to the respective type-mean solutions. Additionally, we analyzed the impact of the applied PCCs on Precise Point Positioning (PPP) station coordinates using our computed orbits. Our preliminary results showed that out of two PPP runs, the one with individual PCCs and respective orbit set reduced the noise in solutions compared to the other PPP run. We conclude that the use of individual PCCs is advantageous for derived GNSS products, as improvements are observed both in the estimated satellite orbits and station coordinate time series. [less ▲]

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See detailComplementary slip distribution of the August 4, 2003 Mw 7.6 and November 17, 2013 Mw 7.8 South Scotia Ridge earthquakes
Ye, Lingling; Lay, Thorne; Koper, Keith D et al

in Earth and Planetary Science Letters (2014), 401

The South Scotia Ridge Transform (SSRT) plate boundary between the Scotia and Antarctic plates experienced large strike-slip earthquakes on August 4, 2003 (Mw 7.6) and November 17, 2013 (Mw 7.8). These ... [more ▼]

The South Scotia Ridge Transform (SSRT) plate boundary between the Scotia and Antarctic plates experienced large strike-slip earthquakes on August 4, 2003 (Mw 7.6) and November 17, 2013 (Mw 7.8). These events have overlapping aftershock zones, which is unusual. A 36°-45° southward dipping fault zone ruptured with left-lateral displacements in each event along the northern margin of the South Orkney micro-continent near 60°S. Slip distributions for the two events are determined using teleseismic body and surface wave recordings along with constraints from GPS ground motion recordings at station BORC on Laurie Island (South Orkney Islands), just south of the SSRT. The aftershock distributions, high-frequency back-projections, and unconstrained body wave finite-fault inversions permit significant overlap of the 2003 and 2013 slip zones; however, the GPS static displacements resolve differences in the large-slip regions of the two ruptures. The 2013 earthquake sequence along the SSRT initiated with Mw 6.1 (November 13) and Mw 6.8 (November 16) foreshocks located ~50 km west of the mainshock hypocenter, and had aftershocks extending ~250 km eastward. The rupture spread primarily eastward at ~2.5 km/s with a total rupture duration of about 120 s, with two distinct patches of large-slip located northwest and northeast of the South Orkney Islands. The rupture swept past BORC, with high-rate GPS (HRGPS) ground motion recordings capturing the time-varying slip history of the faulting. Traditional GPS data require that the largest-slip region of the shorter rupture in 2003 is located in the gap NNE of BORC between the two patches that ruptured in 2013. There appears to be some overlap of lower slip regions. The complementary slip distributions comprise a relatively uniform offset along this portion of the SSRT, which is one of the most seismically active regions of the entire Antarctic plate boundary. [less ▲]

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See detailNear Field Dynamic, Co-seismic and Post-seismic Deformations Associated with the 2013, M7.8, and 2003, M7.6, South Scotia Ridge Earthquakes Observed with GPS
Smalley, Robert Jr; Bevis, Mike G; Zakrajsek, A F et al

Poster (2014, September)

The South Scotia Ridge (SSR) left-lateral transform/strike-slip (S-S) fault defines the Scotia plate’s (SP) southern boundary separating it from the Powell Basin (PB), South Orkney Microcontinent (SOM ... [more ▼]

The South Scotia Ridge (SSR) left-lateral transform/strike-slip (S-S) fault defines the Scotia plate’s (SP) southern boundary separating it from the Powell Basin (PB), South Orkney Microcontinent (SOM), and the Weddell Sea sections of the Antarctic plate (AP). The SP developed as a space filling accommodation zone for S. America-Antarctica relative motions, mostly during the last 40 m.y. The SSR also hosts several restraining and releasing bends. The SP, PB and SOM have complex evolution histories including large-scale displacement and stretching of the SOM, as well as other continental fragments within the SP, all of which were incorporated into a background of changing sea floor spreading geometries. The SOM defines an ~300 km segment of the SSR opposite a section of the SP that is primarily oceanic crust with a few small, stretched continental fragments. Two large earthquakes, M7.6 and 7.8, with aftershock zones largely confined to the northern SOM boundary, occurred on the SSR in 2003 and 2013. Moment tensor solutions show they occurred on faults dipping ~30 and 45° to the south. The 2013 event was almost pure, left-lateral strike-slip, while the 2003 event was oblique but predominantly strike-slip. This is an unusual combination of fault dip and slip direction for a strike-slip plate boundary. The half duration of both events is also relatively long. A continuous GPS (CGPS) station on Laurie Island is located immediately west of the rupture zone of the 2003 event and at the approximate center, and close to the surface projection, of the finite fault models for the 2013 earthquake. We present co-seismic static offsets and post-seismic transients for both earthquakes from GPS daily position estimates. In addition, the CGPS station now records at 1 Hz and we present the GPS displacement seismogram for the 2013 event. This record contains a complex signal that includes the passage of the Love and Rayleigh surface waves, with max displacements of ~70 cm, over an ~80 second time interval during which a ~50 cm static offset developed. [less ▲]

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See detailRecent Activities at the King Edward Point Geodetic Observatory, South Georgia, in Support of TIGA Objectives
Teferle, Felix Norman UL; Hunegnaw, Addisu UL; Williams, Simon et al

Poster (2014, July 26)

In 2013 the King Edward Point (KEP) Geodetic Observatory was established in South Georgia, South Atlantic Ocean, in support of geoscience applications. South Georgia Island has been a key location for the ... [more ▼]

In 2013 the King Edward Point (KEP) Geodetic Observatory was established in South Georgia, South Atlantic Ocean, in support of geoscience applications. South Georgia Island has been a key location for the seismic, geomagnetic and oceanic global monitoring networks. However, no geodetic permanent monitoring station had been established there despite the lack of observations from this region within the International GNSS Service (IGS) network of Global Navigation Satellite System (GNSS) stations. Currently, the observatory consists of two state-of-the-art GNSS stations (KEPA 42701M001 and KRSA 42702M001) with local benchmark networks, allowing the height determinations from the GNSS antennas to be transferred to the tide gauge (Global Sea Level Observing System 187) and forming a height reference within the International Terrestrial Reference Frame. In this study, we will present an evaluation of the GNSS observations from the KEP Geodetic Observatory for the period from February 2013 to December 2013. We calculate multipath and positioning statistics and compare these to those from IGS stations. We report on the benchmark network and tide board installation, as well as, on the results from the two levelling campaigns carried out to date. For the future it is envisaged that the stations will contribute to the TIGA objective of monitoring vertical land movements at tide gauges, and that KEPA will contribute to the IGS network. [less ▲]

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See detailSUGAC: Sofia University GNSS Analysis Center
Simeonov, Tzvetan; Sidorov, Dmitry UL; Teferle, Felix Norman UL et al

Poster (2014, June 25)

The Sofia University GNSS Analysis Centre (SUGAC, suada.phys.uni-sofia.bg) is a new analysis centre established via collaboration between the Department of Meteorology and Geophysics of Sofia University ... [more ▼]

The Sofia University GNSS Analysis Centre (SUGAC, suada.phys.uni-sofia.bg) is a new analysis centre established via collaboration between the Department of Meteorology and Geophysics of Sofia University, the IPOS - BuliPOS GNSS network in Bulgaria and the University of Luxembourg. In April 2014, the first processing campaign took place. One year GNSS data from 7 stations of the BuliPOS network are processed in collaboration with the University of Luxembourg. Tropospheric products (Zenith Total Delay and gradients) with 5 min temporal resolution are obtained using the NAPEOS software, developed by ESA. The tropospheric products from this campaign will be used for validation of the Weather Research and Forecasting (WRF) model as well as for case studies during intense precipitation events and fog. In this work the WRF model validation for Bulgaria will be presented. Future work will be the establishment of autonomous near real-time processing of the regional ground-based GNSS network in Southeast Europe in support of the EUMETNET E-GVAP and COST ES1206 ”Advanced Global Navigation Satellite Systems for Severe Weather Events and Climate” projects. [less ▲]

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See detailAssimilation of zenith total delays in the AROME France convective scale model: a recent assessment
Mahfouf, Jean-François; Ahmed, Furqan UL; Moll, Patrick et al

Poster (2014, February)

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See detailGeological interpretation of current subsidence and uplift in the London area, UK, as shown by high precision satellite-based surveying
Aldiss, Don; Burke, Helen; Chacksfield, Barrie et al

in Proceedings of the Geologists' Association (2014), 125(1), 1-13

Abstract Long term planning for flood risk management in coastal areas requires timely and reliable information on changes in land and sea levels. A high resolution map of current changes in land levels ... [more ▼]

Abstract Long term planning for flood risk management in coastal areas requires timely and reliable information on changes in land and sea levels. A high resolution map of current changes in land levels in the London and Thames estuary area has been generated by satellite-based persistent scatterer interferometry (PSI), aligned to absolute gravity (AG) and global positioning system (GPS) measurements. This map has been qualitatively validated by geological interpretation, which demonstrates a variety of controlling influences on the rates of land level change, ranging from near-surface to deep-seated mechanisms and from less than a decade to more than 100,000 years’ duration. During the period 1997–2005, most of the region around the Thames estuary subsided between 0.9 and 1.5 mm a−1 on average, with subsidence of thick Holocene deposits being as fast as 2.1 mm a−1. By contrast, parts of west and north London on the Midlands Microcraton subsided by less than 0.7 mm a−1, and in places appear to have risen by about 0.3 mm a−1. These rates of subsidence are close to values determined previously by studies of Quaternary sequences, but the combined GPS, AG and PSI land level change data demonstrate a new level of local geological control that was not previously resolvable. [less ▲]

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See detailA drifting GPS buoy for retrieving effective riverbed bathymetry
Hostache, R.; Matgen, P.; Giustarini, L. et al

in Journal of Hydrology (2014), (0), -

Spatially distributed riverbed bathymetry information are rarely available but mandatory for accurate hydrodynamic modeling. This study aims at evaluating the potential of the Global Navigation Satellite ... [more ▼]

Spatially distributed riverbed bathymetry information are rarely available but mandatory for accurate hydrodynamic modeling. This study aims at evaluating the potential of the Global Navigation Satellite System (GNSS), like for instance Global Positioning System (GPS), for retrieving such data. Drifting buoys equipped with navigation systems such as GPS enable the quasi-continuous measurement of water surface elevation, from virtually any point in the world. The present study investigates the potential of assimilating GNSS-derived water surface elevation measurements into hydraulic models in order to retrieve effective riverbed bathymetry. First tests with a GPS dual-frequency receiver show that the root mean squared error (RMSE) on the elevation measurement equals 30 cm provided that a differential post processing is performed. Next, synthetic observations of a drifting buoy were generated assuming a 30 cm average error of Water Surface Elevation (WSE) measurements. By assimilating the synthetic observation into a 1D-Hydrodynamic model, we show that the riverbed bathymetry can be retrieved with an accuracy of 36 cm. Moreover, the WSEs simulated by the hydrodynamic model using the retrieved bathymetry are in good agreement with the synthetic ‘‘truth’’, exhibiting an RMSE of 27 cm. [less ▲]

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See detailComparative Analysis of Real-Time Precise Point Positioning Zenith Total Delay Estimates
Ahmed, Furqan UL; Vaclavovic, Pavel; Teferle, Felix Norman UL et al

Poster (2013, December 13)

The use of observations from Global Navigation Satellite Systems (GNSS) in operational meteorology is increasing worldwide due to the continuous evolution of GNSS. The assimilation of near real-time (NRT ... [more ▼]

The use of observations from Global Navigation Satellite Systems (GNSS) in operational meteorology is increasing worldwide due to the continuous evolution of GNSS. The assimilation of near real-time (NRT) GNSS-derived zenith total delay (ZTD) estimates into local, regional and global scale numerical weather prediction (NWP) models is now in operation at a number of meteorological institutions. The development of NWP models with high update cycles for nowcasting and monitoring of extreme weather events in recent years, requires the estimation of ZTD with minimal latencies, i.e. from 5 to 10 minutes, while maintaining an adequate level of accuracy for these. The availability of real-time (RT) observations and products from the IGS RT service and associated analysis centers make it possible to compute precise point positioning (PPP) solutions in RT, which provide ZTD along with position estimates. This study presents a comparison of the RT ZTD estimates from three different PPP software packages (G-Nut/Tefnut, BNC2.7 and PPP-Wizard) to the state-of-the-art IGS Final Troposphere Product employing PPP in the Bernese GPS Software. Overall, the ZTD time series obtained by the software packages agree fairly well with the estimates following the variations of the other solutions, but showing various biases with the reference. After correction of these the RMS differences are at the order of 0.01 m. The application of PPP ambiguity resolution in one solution or the use of different RT product streams shows little impact on the ZTD estimates. [less ▲]

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