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See detailNumerical investigation of bridges with the aim of condition assessment in applying the Deformation Area Difference method (DAD-method) and selecting appropriate measurement techniques
Erdenebat, Dolgion UL; Waldmann, Danièle UL; Teferle, Felix Norman UL

in 5th International Symposium on Life-Cycle Civil Engineering (IALCCE 2016), Delft (2016, October)

Condition assessment of existing road bridges gains ever increasing importance today as bridges are getting older and the inflow of heavy traffic is constantly increasing. The further development of ... [more ▼]

Condition assessment of existing road bridges gains ever increasing importance today as bridges are getting older and the inflow of heavy traffic is constantly increasing. The further development of recognized techniques and the development of new methods for early and accurate detection of damage to the structure are made possible by means of innovative technological progress. In this contribution, the principles of Defor-mation Area Difference Method (DAD-Method) for condition assessment of bridges are presented. This method is based on the further processing of measured and computed deformation values. The application of the DAD-Method requires a precise recording of the deflection of a load-deflection test. On the basis of theoretical cal-culations, this method has allowed to identify as well as to localise damage to a structure. The DAD-Method is independent of a reference measurement and insensitive to global influences such as temperature fluctuations. For precise detection of deformations, the most modern measuring instruments and methods like photogram-metry, total stations, displacement sensors, strain gauges and levelling are compared to each other. In collabo-ration with the appropriate measurement technology, the localisation of damage in bridges becomes possible. [less ▲]

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See detailA New Vertical Land Movements Data Set from a Reprocessing of GNSS at Tide Gauge Stations
Hunegnaw, Addisu UL; Klos, Anna; Hansen, Dionne et al

Scientific Conference (2016, July 30)

The main objective of the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group is to provide accurate coordinates and changes in them in the form of long-term trends for ... [more ▼]

The main objective of the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group is to provide accurate coordinates and changes in them in the form of long-term trends for globally distributed Global Navigation Satellite System (GNSS) stations at or close to tide gauges (TGs). Mean sea level (MSL) records derived from TG observations measure sea level relative to benchmarks on the land and structures supporting the TGs. Therefore, any changes in land levels affect the MSL records and the computed estimates of sea level change, ie. the MSL trends. In order to compute regionally or globally averaged MSL required for climate studies, these MSL trends have to be corrected for the vertical land movements (VLMs) derived from the GNSS observations. In this study, we have estimated a new set of VLMs at or close to TGs from the recent reprocessing campaign “repro2” undertaken by British Isles continuous GNSS Facility and University of Luxembourg TIGA Analysis Center (BLT). The position time series of more than 700 stations distributed around the world have been reprocessed for the period 1994 to 2015 using the latest bias models and processing strategies following the conventions of the International Earth Rotation and Reference Frame Service (IERS). It is well known that position time series are affected by discontinuities, which stem from different sources such as earthquakes, hardware changes and other artificial offsets that do not reflect real geophysical events. Since uncorrected discontinuities adversely affect the trend estimates, we have, after applying all known offset epochs, inspected the time series of all stations manually and added any further offset epochs required during the analysis. We have included a total of 2500+ discontinuities of which two-thirds are from hardware changes, 4% from earthquakes and 9% from unknown sources. We fit a deterministic model (sum of linear trend and seasonal terms) to the position time series using the Hector software package. As expected the annual terms show the highest power with amplitudes of a few millimeters. The stochastic model for estimating trend and associated uncertainties follows a power-law noise process as has previously been described as optimal for GNSS-derived position time series. The new set of VLM estimates from our repro2 solution is evaluated through comparison with a published GNSS solution, the recent ICE-6G model of glacial isostatic adjustment and by application to the latest release of MSL trends from the Permanent Service For Mean Sea Level. [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 detailOn the Properties of Zenith Total Delay Time Series from Reprocessed GPS Solutions
Klos, Anna; Teferle, Felix Norman UL; Hunegnaw, Addisu UL et al

Poster (2016, July 29)

Global Positioning System observations from stations in regional and global networks have proven to sense the conditions of the atmosphere, especially the water vapour content of the troposphere. Zenith ... [more ▼]

Global Positioning System observations from stations in regional and global networks have proven to sense the conditions of the atmosphere, especially the water vapour content of the troposphere. Zenith Total Delay (ZTD) derived during the processing of GPS data is a measure of the total atmospheric delay along the signal path between satellite and receiver antennas and arises mostly from the hydrostatic and wet parts of the atmosphere. Having taken surface pressure and temperature into account, ZTD can be converted into an estimate of the Integrated Water Vapour (IWV) content of the atmosphere, which when derived from homogenously reprocessed GPS observations, is emerging as an important parameter in the monitoring of climate change. Especially, the long-term trend and variations in IWV together with their associated uncertainties are of high interest as atmospheric water vapour is the dominant greenhouse gas. To date the trend estimates and their uncertainties are widely determined with assumption that the stochastic properties of the time series follow a random, ie. white noise, process. However, if ZTD and IWV are directly linked to climate processes, one would expect that the underlying noise process has similar character to that found in other climate parameters, which have been modelled by means of an autoregressive process. If this proves to be true, the trend estimates and their uncertainties in ZTD and IWV may have been underestimated up to this day of an order of magnitude. In this research, we examine the properties of both deterministic and stochastic parameters of the ZTDs that were estimated by the consortium of the British Isles continuous GNSS Facility (BIGF) and the University of Luxembourg TIGA Analysis Centres (BLT) for GPS data collected by a global tracking network of more than 700 stations (repro2 solution). The analysis has been started with the homogenisation of the ZTD time series, which is an important task to provide homogeneity over the long-term. Here we used all previously reported discontinuities for a single station along with those added after manually inspecting the time series. This procedure did lead to a total number of 2505 discontinuities for this data set. Next, all significant oscillations were identified with spectral analysis and thereafter modelled with a Least-Squares Method. The residuals were subjected to noise analysis with different stochastic models. The results showed that an autoregressive model of fourth order combined with a white noise process is the optimal model for the ZTD time series. Finally, we provide an optimum evaluation of the ZTD trends and their uncertainties for selected climate zones, which were established according to the Köppen-Geiger climate classification. [less ▲]

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See detailImpact of Limited Satellite Visibility on Estimates of Vertical Land Movements
Abraha, Kibrom Ebuy UL; Teferle, Felix Norman UL; Hunegnaw, Addisu UL et al

in International Association of Geodesy Symposia (2016)

The number of Global Navigation Satellite System (GNSS) satellites and their geometry directly affect the quality of positioning and derived satellite products. Accordingly, the International GNSS Service ... [more ▼]

The number of Global Navigation Satellite System (GNSS) satellites and their geometry directly affect the quality of positioning and derived satellite products. Accordingly, the International GNSS Service (IGS) recommends GNSS antennas to be installed away from natural and man-made surfaces and structures, which may affect the incoming signals through severe multipath or obstructions. Following these recommendations, continuous GNSS (cGNSS) stations are generally located in low multipath environments with minimal signal obstructions. However, some applications require GNSS antennas to be installed at specific locations in order to measure local processes. In support of sea level studies, cGNSS stations are established at or close to tide gauges in order to accurately monitor the local vertical land movements experienced by the sea level sensors. However, the environment at the tide gauge might not be optimal for GNSS observations due to the aforementioned station-specific effects, which may degrade the quality of coordinate solutions. This study investigates the impact of severe signal obstructions on long-term position time series for some selected stations. A masking profile from an actually obstructed site is extracted, simulated and applied to unobstructed IGS sites. To investigate these effects, we imple- mented a new feature called azimuth-dependent elevation masking in the Bernese GNSS Software version 5.2. We present our preliminary results on the use of this new feature to study the impact of different obstruction scenarios on long-term GNSS position time series and vertical land movement estimates. The results show that a certain obstruction, with the effect being highly dependent on its severity and azimuthal direction, affects all coordinate components with the effect being more significant for the Up component. Moreover, it causes changes in the rate estimates and increases the rate uncertainty with the effect being site-specific. [less ▲]

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See detailAccessing of Post-SPeoiswmeirc-LDaewfoPrrmoapteiortnies in Land Movements
Klos, Anna UL; Hunegnaw, Addisu UL; Bos, Machiel et al

Presentation (2016, June)

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See detailStatus of TIGA activities at the British Isles continuous GNSS Facility and the University of Luxembourg
Hunegnaw, Addisu UL; Teferle, Felix Norman UL; Bingley, Richard et al

in International Association of Geodesy Symposia (2016), 143

In 2013 the InternationalGNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group started their reprocessing campaign which proposes to reanalyse all relevant GPS observations from 1995 to ... [more ▼]

In 2013 the InternationalGNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group started their reprocessing campaign which proposes to reanalyse all relevant GPS observations from 1995 to the end of 2012 in order to provide high quality estimates of vertical land motion for monitoring of sea level changes. The TIGA Working Group will also produce a combined solution from the individual TIGA Analysis Centres (TAC) contributions. The consortium of British Isles continuous GNSS Facility (BIGF) and the University of Luxembourg TAC (BLT) will contribute weekly minimally constrained SINEX solutions from its reprocessing using the Bernese GNSS Software (BSW) version 5.2 and the University of Luxembourg will also act as a TIGA Combination Centre (TCC). The BLT will generate two solutions, one based on BSW5.2 using a network double difference (DD) strategy and a second one based on BSW5.2 using a Precise Point Positioning (PPP) strategy. In the DD strategy we have included all IGb08 core stations in order to achieve a consistent reference frame implementation. As an initial test for the TIGA combination, all TACs agreed to provide weekly SINEX solutions for a four-week period in December 2011. Taking these individual TAC solutions the TCC has computed a first combination using two independent combination software packages: CATREF and GLOBK. In this study we will present preliminary results from the BLT reprocessing and from the combination tests [less ▲]

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See detailCombination of Tide Gauge Benchmark Monitoring (TIGA) Analysis Center from repro2 solutions
Hunegnaw, Addisu UL; Teferle, Felix Norman UL

Poster (2016, April 19)

Recently the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group (WG) has completed their repro2 solutions by re-analyzing the full history of all relevant Global ... [more ▼]

Recently the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group (WG) has completed their repro2 solutions by re-analyzing the full history of all relevant Global Positioning System (GPS) observations from 1995 to 2015. This re-processed data set will provide high-quality estimates of vertical land movements for more than 700 stations, enabling regional and global high-precision geophysical/geodetic studies. All the TIGA Analysis Centres (TACs) have processed the observations recorded by GPS stations at or close to tide gauges, which are available from the TIGA Data Center at the University of La Rochelle (www.sonel.org) besides those of the global IGS core network used for its reference frame implementations. Following the recent improvements in processing models, strategies (http://acc.igs.org/reprocess2.html), this is the first complete reprocessing attempt by the TIGA WG to provide homogeneous position time series relevant to sea level changes. In this study we report on a first multi-year daily combined solution from the TIGA Combination Centre (TCC) at the University of Luxembourg (UL) with respect to the latest International Terrestrial Reference Frame (ITRF2014). Using GLOBK combination software package, we have computed a first daily combined solution from TAC solutions already available to the TIGA WG. These combinations allow an evaluation any effects of the individual TAC parameters and their influences on the combined solution with respect to the latest ITRF2014. Some results of the UL TIGA multi-year combinations in terms of geocentric sea level changes will be presented and discussedd [less ▲]

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See detailThe Combined Effect of Periodic Signals and Noise on the Dilution of Precision of GNSS Station Velocity Uncertainties
Klos, Anna; Olivares Pulido, German UL; Teferle, Felix Norman UL et al

Poster (2016, April 05)

Station velocity uncertainties determined from a series of Global Navigation Satellite System (GNSS) position estimates depend on both the deterministic and stochastic models applied to the time series ... [more ▼]

Station velocity uncertainties determined from a series of Global Navigation Satellite System (GNSS) position estimates depend on both the deterministic and stochastic models applied to the time series. While the deterministic model generally includes parameters for a linear and several periodic terms, the stochastic model is a representation of the noise character of the time series in form of a power-law process. For both of these models the optimal model may vary from one time series to another while the models also depend, to some degree, on each other. In the past various power-law processes have been shown to fit the time series and the sources for the apparent temporally-correlated noise were attributed to, for example, mismodelling of satellites orbits, antenna phase centre variations, troposphere, Earth Orientation Parameters, mass loading effects and monument instabilities. [less ▲]

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See detailA First Evaluation of the new GNSS Station Installations at the Tide Gauges of Walvis Bay and Lüderitz in the Republic of Namibia
Teferle, Felix Norman UL; Combrinck, Ludwig; Botha, Roelf et al

Poster (2016, February 11)

During September 2015 the Hartebeesthoek Radio Astronomy Observatory in collaboration with the University of Luxembourg installed two state-of-the-art continuous GNSS stations adjacent to the tide gauges ... [more ▼]

During September 2015 the Hartebeesthoek Radio Astronomy Observatory in collaboration with the University of Luxembourg installed two state-of-the-art continuous GNSS stations adjacent to the tide gauges of Walvis Bay and Lüderitz in the Republic of Namibia. These installations are the culmination of a four-year effort to get the stations established and the help of the Namibian Port Authority in this endeavour is much appreciated. The tide gauge at Walvis Bay (Global Sea Level Observing System (GLOSS) number 314) has a record in the Permanent Service for Mean Sea Level (PSMSL) Revised Local Reference (RLR) database (number 914) dating back to 1958 (data completeness 54%). The tide gauge at Lüderitz is not a GLOSS station but also has a PSMSL RLR record (number 911) since 1958 (data completeness 67%). Both tide gauges currently use a radar measurement unit and are operated by the Hydrographic Office of the South African Navy. They are the only sea level observations along a more than 3000 km stretch of the West African coast from Pointe Noire in the Republic of the Congo to Port Nolloth in the Republic South Africa, hence they form an important data source for sea level studies. The two continuous GNSS stations record observations from all visible GNSS satellites (GPS, GLONASS, BDS and Galileo) with a 1 second recording interval. The current installations support hourly data downloads, which are sufficient for most activities within the IGS, while the data have great potential to contribute not only to the TIGA working group but also to MGEX. In this study we present the first evaluation of the quality of the GNSS observations from the two new continuous GNSS stations for the first three months of operation. In the future we plan to make the data available to the scientific community. [less ▲]

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See detailTotal Impact of Periodic Terms and Coloured Noise on Velocity Estimates
Klos, Anna; Olivares, German; Teferle, Felix Norman UL et al

Poster (2016, February 05)

The uncertainties of velocity estimates for position time series of Global Navigation Satellite System (GNSS) stations are mainly affected by a misfit of the deterministic model applied to this data ... [more ▼]

The uncertainties of velocity estimates for position time series of Global Navigation Satellite System (GNSS) stations are mainly affected by a misfit of the deterministic model applied to this data. Insufficiently modelled seasonal signals will propagate into the stochastic model and falsify the results of the noise analysis besides the velocity estimates and their uncertainties. In this presentation we derived the General Dilution of Precision (GDP) of velocity uncertainties. We define this dilution as the ratio between the uncertainties of velocities determined when different deterministic and stochastic models are applied. In this way we discuss, referring to previously published results, how insufficiently modelled seasonal signals influence station velocity uncertainties with white and coloured noise. Using simulated and real data from selected (115) IGS (International GNSS Service) stations we show that the noise character affects GNSS data more than seasonals for time series longer than 9 years. [less ▲]

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See detailQuality assessment of Mulit-Year BLT Tide Gauge Benchmark Monitoring (TIGA) repro2 Solution
Hunegnaw, Addisu UL; Teferle, Felix Norman UL

Poster (2016, February)

Recently the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group (WG) has completed their repro2 solutions by re-analyzeing the full history of all relevant Global ... [more ▼]

Recently the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group (WG) has completed their repro2 solutions by re-analyzeing the full history of all relevant Global Positioning System (GPS) observations from 1995 to 2015. This re-processed data set will provide high-quality estimates of vertical land movements for more than 500 stations, enabling regional and global high-precision geophysical/geodetic studies. All the TIGA Analysis Centres (TACs) have mainly processed the GPS observations recorded by 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, strategies (http://acc.igs.org/reprocess2.html), this is the first complete re-processing attempt by the TIGA WG to provide homogeneous position time series relevant to sea level changes. In this study we report on a first multi-year daily combined solution from the TIGA Combination Centre (TCC) at the University of Luxembourg (UL) with respect to the latest International Terrestrial Reference Frame (ITRF2014). Using two independent combination software packages, CATREF and GLOBK, we have computed a first daily combined solution from TAC solutions already available for TIGA WG. 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 with respect to the latest ITRF2014. Some 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 detailThe Status of GNSS Data Processing Systems to Estimate Integrated Water Vapour for Use in Numerical Weather Prediction Models
Ahmed, Furqan UL; Teferle, Felix Norman UL; Bingley, Richard et al

in Willis, Pascal; Rizos, Chris (Eds.) IAG 150 Years Proceedings of the 2013 IAG Scientific Assembly, Postdam,Germany, 1–6 September, 2013 (2016)

Modern Numerical Weather Prediction (NWP) models make use of the GNSS-derived Zenith Total Delay (ZTD) or Integrated Water Vapour (IWV) estimates to enhance the quality of their forecasts. Usually, the ... [more ▼]

Modern Numerical Weather Prediction (NWP) models make use of the GNSS-derived Zenith Total Delay (ZTD) or Integrated Water Vapour (IWV) estimates to enhance the quality of their forecasts. Usually, the ZTD is assimilated into the NWP models on 3-hourly to 6-hourly intervals but with the advancement of NWP models towards higher update rates e.g. 1-hourly cycling in the Rapid update Cycle (RUC) NWP, it has become of high interest to estimate ZTD on sub-hourly intervals. In turn, this imposes requirements related to the timeliness and accuracy of the ZTD estimates and has lead to a development of various strategies to process GNSS observations to obtain ZTD with different latencies and accuracies. Using present GNSS products and tools, ZTD can be estimated in realtime (RT), near real-time (NRT) and post-processing (PP) modes. The aim of this study is to provide an overview and accuracy assessment of various RT, NRT, and PP IWV estimation systems and comparing their achieved accuracy with the user requirements for GNSS meteorology. The NRT systems are based on Bernese GPS Software 5.0 and use a double-differencing strategy whereas the PP system is based on the Bernese GNSS Software 5.2 using the precise point positioning (PPP) strategy. The RT systems are based on the BKG Ntrip Client 2.7 and the PPP-Wizard both using PPP. The PPP-Wizard allows integer ambiguity resolution at a single station and therefore the effect of fixing integer ambiguities on ZTD estimates will also be presented. [less ▲]

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See detailThe King Edward Point Geodetic Observatory, South Georgia, South Atlantic Ocean: A First Evaluation and Potential Contributions to Geosciences
Teferle, Felix Norman UL; Hunegnaw, Addisu UL; Ahmed, Furqan UL et al

in Willis, Pascal; Rizos, Chris (Eds.) IAG 150 Years Proceedings of the 2013 IAG Scientific Assembly, Postdam, Germany, 1–6 September, 2013 (2016)

During February 2013 the King Edward Point (KEP) Geodetic Observatory was established in South Georgia, South Atlantic Ocean, through a University of Luxembourg funded research project and in ... [more ▼]

During February 2013 the King Edward Point (KEP) Geodetic Observatory was established in South Georgia, South Atlantic Ocean, through a University of Luxembourg funded research project and in collaboration with the United Kingdom National Oceanography Centre, British Antarctic Survey, and Unavco, Inc. Due to its remote location in the South Atlantic Ocean, as well as being one of few subaerial exposures of the Scotia tectonic plate, South Georgia Island has been a key location for a number of global monitoring networks, e.g. seismic, geomagnetic and oceanic. However, no permanent geodetic monitoring station has been established previously, despite the lack of observations from this region. In this study we will present an evaluation of the GNSS and meteorological observations from the KEP Geodetic Observatory for the period from 14 February to 31 December 2013. We calculate multipath and positioning statistics and compare these to those from IGS stations using equipment of the same type. The on-site meteorological data are compared to those from the nearby KEP meteorological station and the NCEP/NCAR reanalysis model, and the impact of these data sets on integrated water vapour estimates is evaluated. We discuss the installation in terms of its potential contributions to sea level observations using tide gauges and satellite altimetry, studies of tectonics, glacio-isostatic adjustment and atmospheric processes. [less ▲]

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See detailImpact of Antenna Phase Centre Calibrations on Position Time Series: Preliminary Results
Sidorov, Dmitry UL; Teferle, Felix Norman UL

in Willis, Pascal; Rizos, Chris (Eds.) IAG 150 Years Proceedings of the 2013 IAG Scientific Assembly, Postdam,Germany, 1–6 September, 2013 (2016)

Advances in GPS error modelling and the continued effort of re-processing have considerably decreased the scatter in position estimates over the last decade. The associated reduction of noise in derived ... [more ▼]

Advances in GPS error modelling and the continued effort of re-processing have considerably decreased the scatter in position estimates over the last decade. The associated reduction of noise in derived position time series has revealed the presence of previously undetected periodic signals. It has been shown that these signals have frequencies related to the orbits of the GPS satellites. A number of potential sources for these periodicities at the draconitic frequency and its harmonics have already been suggested in the literature and include, e.g., errors in the sub-daily tidal models, multipath and unresolved integer ambiguities. Due to the geometrical relationship between the observing site and the orbiting satellite, deficiencies in the modelling of electromagnetic phase centres of receiving antennas have the potential to also contribute to the discovered periodic signals. The change from relative to absolute type mean antenna/radome calibrations within the International GNSS Service (IGS) led to a significant improvement, but the use of individual calibrations could possibly add further refinements to computed solutions. However, at this stage providing individual calibrations for all IGS stations is not feasible. Furthermore, antenna near-field electromagnetic effects might outweigh the benefits of individual calibrations once an antenna is permanently installed. In this study, we investigate the differences between position estimates obtained using individual and type mean antenna/radome calibrations as used by the IGS community. We employ position time series derived from precise point positioning (PPP) as implemented in two scientific GNSS software packages. Our results suggest that the calibration differences propagate directly into the position estimates, affecting both sub-daily and daily results and yielding periodic variations. The sub-daily variations have periods close to half a sidereal day and one sidereal day with peak-to-peak amplitudes of up to 10~mm in all position components. The stacked power spectra of the daily difference time series reveal peaks at the GPS draconitic frequency and its harmonics with peak-to-peak amplitudes of up to 1~mm. Although these results are still preliminary, they confirm that small differences between individual and type mean antenna/radome calibrations propagate into position time series and may be partly responsible for the spurious signals with draconitic frequency and its harmonics. [less ▲]

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

Poster (2015, December 17)

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 detailSignal Obstructions at GNSS Stations: Benefits From Multi-GNSS Observations
Abraha, Kibrom Ebuy UL; Teferle, Felix Norman UL; Hunegnaw, Addisu UL et al

Poster (2015, October 27)

The current accuracy of IGS products, few centimeter level, requires amongst other things that the location for GNSS antennas are nearly optimal for GNSS observations. This includes a low multipath ... [more ▼]

The current accuracy of IGS products, few centimeter level, requires amongst other things that the location for GNSS antennas are nearly optimal for GNSS observations. This includes a low multipath environment and little to no signal obstructions. However, this is not guaranteed for every station especially in urban areas and mountainous regions. As some applications such as GNSS for sea level studies or to monitor landslides require GNSS antennas to be installed at a specific site, it is clear that the environment might not be favourable for GNSS observations. In this study, we investigate the effect of signal obstructions on station positions, specifically the height component, based on simulated obstruction scenarios using a modified Bernese GNSS Software version 5.2 (BSW52). The behaviours of different obstruction scenarios and the impact of multi-GNSS (GPS+GLONASS for now) observations for both clear and obstructed stations are discussed. [less ▲]

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See detailImpact of Limited Multi-GNSS Visibility on Vertical Land Movement Estimates
Abraha, Kibrom Ebuy UL; Teferle, Felix Norman UL; Hunegnaw, Addisu UL et al

Poster (2015, June 27)

The number of GNSS satellites and their geometry directly affect the quality of positioning and derived satellite products. Accordingly, the International GNSS Service (IGS) recommends GNSS antennas to be ... [more ▼]

The number of GNSS satellites and their geometry directly affect the quality of positioning and derived satellite products. Accordingly, the International GNSS Service (IGS) recommends GNSS antennas to be installed away from natural and man-made surfaces and structures, which may affect the incoming signals through severe multipath or obstructions. Following these recommendations, continuous GNSS (cGNSS) stations are generally located in low multipath environments with minimal signal obstructions. However, some applications require GNSS antennas to be installed at specific locations in order to measure local processes. Hence, in support of sea level studies, cGNSS stations must be installed close to or at tide gauges in order to accurately monitor the local vertical land movements experienced by the sea level sensors. However, the environment at the tide gauge might not be optimal for GNSS observations due to the aforementioned station-specific effects, which degrade the quality of coordinate solutions.This first study investigates the impact of severe signal obstructions on long-term monitoring results by use of simulated and real observations for selected cGNSS stations, and evaluates if the use of multi-GNSS (GPS+GLONASS) constellations will benefit derived results. To investigate these effects, we implemented azimuth and elevation dependent masking in the Bernese GNSS Software version 5.2. We present our preliminary results on the impact of different obstruction scenarios and combined GPS and GLONASS solutions on coordinate and vertical land movement estimates. [less ▲]

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

Poster (2015, June 27)

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. This ties all benchmarks and the tide gauge into the International Terrestrial Reference Frame 2008, and allows the establishment of a local height datum in a global height system through the use of a global gravitational model. In 2014 a tide board was added to the tide gauge, which, together with the GNSS and levelling observations, 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. 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 derived from a seamless combination of the latest Gravity Observation Combination (GOCO) 05S and Earth Gravitational Model (EGM) 2008 models. [less ▲]

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