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See detailPresent-Day Land and Sea Level Changes around South Georgia Island: Results from Precise Levelling, GNSS, Tide Gauge and Satellite Altimetry Measurements
Teferle, Felix Norman UL; Dalziel, I W D; Hunegnaw, Addisu UL et al

Scientific Conference (2019, July 25)

South Georgia Island, the main land outcrop on the South Georgia microcontinent (SGM), is located approximately 1,400 km east of the Falkland Islands and approximately 1,400 km northeast of the ... [more ▼]

South Georgia Island, the main land outcrop on the South Georgia microcontinent (SGM), is located approximately 1,400 km east of the Falkland Islands and approximately 1,400 km northeast of the northernmost tip of the Antarctic peninsular. The SGM is believed to lie south of the North Scotia Ridge (NSR), which forms the boundary to the South America Plate, while to the south it is bordered by the Scotia Plate (SP). In its sub-Antarctic location, the island is largely covered by mountain glaciers which have been reported to be retreating due to climatic change. Furthermore, during past glaciation periods the island and its shelf area, stretching much of the SGM, have been ice covered as was revealed by scarring of the sub-oceanic topography. Together with ongoing tectonics along the NSR and recent seismicity at the SP boundary, these processes have the ability to produce significant uplift on local to regional scales. With its mid-ocean location in the Southern Atlantic Ocean South Georgia Island is in a key position for the oceanic and geodetic global monitoring networks. As these net-works suffer from a Hemisphere imbalance with the number of stations in the Northern Hemisphere outnumbering those in the Southern Hemisphere, operating these stations to the highest standards is of key scientific value. It is of particular interest to monitor the tide gauge (GLOSS ID 187) at King Edward Point (KEP) for vertical land movements to establish a continuous record of its datum within the Permanent Service for Mean Sea Level (PSMSL), which in turn makes it useful for long-term sea level studies and satellite altimetry calibrations. With the establishment of five GNSS stations on the islands by teams from Luxembourg, the UK and the USA during 2013 to 2015, and the scientific analysis of these data within a global network of stations, it has now become possible to study present-day vertical land movements and their impacts. Furthermore, together with four precise levelling campaigns of the KEP benchmark network in 2013, 2014 and two in 2017, it has also been possible to investigate the very local character of the vertical motions near KEP, i.e. the stability of the jetty upon which the tide gauge is mounted. In this study, we will present the still preliminary results from the GNSS and levelling measurements and will discuss their impact on the sea level record from the KEP tide gauge. Our measurements show that while South Georgia Island and the area around KEP are rising, the jetty and tide gauge are subsiding, leading to a lower magnitude of the observed sea level change than expected from satellite altimetry. In order to improve the agreement between these measurements both local and regional vertical land movements need to be monitored. [less ▲]

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See detailRecent Activities on Tristan da Cunha Island: Geodetic Installations, Local Tie Measurements and their Analysis
Teferle, Felix Norman UL; Hunegnaw, Addisu UL; Backes, Dietmar UL et al

Scientific Conference (2019, July 11)

During 2017 a team from the University of Luxembourg and the National Oceanography Centre, Liverpool, established a permanent Global Navigation Satellite System (GNSS) station and two new tide gauges on ... [more ▼]

During 2017 a team from the University of Luxembourg and the National Oceanography Centre, Liverpool, established a permanent Global Navigation Satellite System (GNSS) station and two new tide gauges on Tristan da Cunha Island in the South Atlantic Ocean. These installations were funded through various projects at both collaborating institutions under the umbrella of the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group and the Global Geodetic Observing System (GGOS) focus area on Sea Level Change, Variability and Forecasting. While this was the first scientific installation of a GNSS station on the main island within the Tristan da Cunha archipelago, IGS station GOUG, located on Gough Island which lies 412 km to the south, has been in operation since 1998. Unfortunately GOUG was decommissioned in 2018. Sea level observations on Tristan da Cunha have a longer history than GNSS with various tide gauges having been in operation since 1984. Tristan da Cunha also hosts a Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) station which was established in 2012 after a previous installation was upgraded and moved to the current site. The antenna TCTA is located on the concrete monument of the previous DORIS antenna. Furthermore, in order for future International Terrestrial Reference Frame (ITRF) computations to fully benefit from the proximity of the sensors, the geodetic ties between the respective antennas (and reference markers in case of the tide gauges) need to be determined at the millimeter level using various terrestrial surveying methods and a local benchmark network. This contribution provides details of the activities on Tristan da Cunha including the installations, the established benchmark network, the terrestrial surveys of the geodetic ties and the analysis of these measurements in order to geometrically link the GNSS and DORIS antennas to each other as well as to the tide gauges. [less ▲]

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See detailThe King Edward Point Geodetic Observatory in Support of Sea Level Research
Teferle, Felix Norman UL; Hunegnaw, Addisu UL; Ahmed, Furqan UL et al

Poster (2013, October 28)

During February 2013 the King Edward Point (KEP) Geodetic Observatory was established in South Geor- gia, 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 Geor- gia, South Atlantic Ocean, through a University of Luxembourg funded research project and in collaboration with the United Kingdom’s 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 plate, South Georgia Island has been a key location for a number of global monitoring networks, e.g. seismic, geomagnetic and oceanic. However, no geodetic monitoring station has been established, e.g. by the International Global Navigation Satellite System (GNSS) Service (IGS) community, despite the lack of such observations from this region. In this study we give details of the establishment of the KEP Geodetic Observatory, i.e. the installation of the continuous GNSS station KEPA on Brown Mountain and the estab- lishment of a new height datum for the tide gauge through a network of benchmarks at the KEP research station. We will present an evaluation of the GNSS positioning results for the period from February to August 2013 and of the survey/levelling work carried out for the height reference. We will 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 detailInstallation and First Evaluation of the King Edward Point Geodetic Observatory, South Georgia
Teferle, Felix Norman UL; White, Seth Warren; Foden, Peter R. et al

Poster (2013, May)

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

During February 2013 the King Edward Point (KEP) Geodetic Observatory was established in South Georgia through a University of Luxembourg funded research project in collaboration with the National Oceanography Centre and the British Antarctic Survey. Due to its remote location in the South Atlantic Ocean as well as being one of few subaerial exposures of the Scotia plate, South Georgia has been a key location for a number of global monitoring networks, e.g. seismic, magnetic and oceanic. However, no geodetic monitoring station had been established previously despite the global network of Global Navigation Satellite System (GNSS) stations is lacking observations from this region. In this presentation we will present a first evaluation of the observations from the KEP Geodetic Observatory for the period from 14 February to 14 April 2013. We calculate multipath characteristics and positioning statistics from precise point positioning (PPP) and discuss the installation in terms of benefits for studies of tectonics and glacio-isostatic adjustment processes. The meteorological data is evaluated by comparison to the data from the existing KEP meteorological station and a widely used numerical weather model. [less ▲]

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Peer Reviewed
See detailNew Estimates of Present-Day Crustal/Land Motions in the British Isles Based on the BIGF Network
Hansen, Dionne; Teferle, Felix Norman UL; Bingley, Richard M et al

in International Association of Geodesy Symposia (2012), 136

n this study we present results from a recent reprocessing effort that included data from more than 120 continuous Global Positioning System (CGPS) stations in the British Isles for the period from 1997 ... [more ▼]

n this study we present results from a recent reprocessing effort that included data from more than 120 continuous Global Positioning System (CGPS) stations in the British Isles for the period from 1997 to 2008. Not only was the CGPS network dramatically densified from previous investigations by the authors, it now also includes, for the first time, stations in Northern Ireland, providing new constraints on glacio-isostatic processes active in the region. In our processing strategy we apply a combination of re-analysed satellite orbit and Earth rotation products together with updated models for absolute satellite and receiver antenna phase centers, and for the computation of atmospheric delays. Our reference frame implementation uses a semi-global network of 37 stations, to align our daily position estimates, using a minimal constraints approach, to ITRF2005. This network uses a combination of current IGS reference frame stations plus additional IGS stations in order to provide similar network geometries throughout the complete time span. The derived horizontal and vertical station velocities are used to investigate present-day crustal/land motions in the British Isles. This first solution provides the basis for our contri- bution to the Working Group on Regional Dense Velocity Fields, 2007 - 2011 of the International Asso- ciation of Geodesy Subcommission 1.3 on Regional Reference Frames. [less ▲]

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Peer Reviewed
See detailDetecting storm surge loading deformations around the southern North Sea using subdaily GPS
Geng, Jianghui; Williams, Simon D. P.; Teferle, Felix Norman UL et al

in Geophysical Journal International (2012), 191(2), 569-578

A large storm surge event occurred on 2007 November 2009 in the southern North Sea where strong winds caused the sea level to rise drastically by up to 3 m within several hours. Based on the Proudman ... [more ▼]

A large storm surge event occurred on 2007 November 2009 in the southern North Sea where strong winds caused the sea level to rise drastically by up to 3 m within several hours. Based on the Proudman Oceanographic Laboratory storm surge model, the predicted loading displacements at coastal stations can reach a few centimetres in the vertical and several millimetres in the horizontal directions. In this study, we used two-hourly global positioning system (GPS) positions at 26 stations around the southern North Sea to identify the loading displacements caused by this storm surge event. We find that the mean rms of the differences between the estimated and predicted displacements are 4.9, 1.3 and 1.4 mm, which are insignificant compared to the one-sigma GPS positioning errors of 5.1, 2.0 and 2.4 mm for the Up, East and North components, respectively. More interestingly, in both vertical and horizontal directions, the estimated displacements successfully tracked the temporal evolution of the storm surge loading effects. In addition, within the whole of 2007 November, we used the predicted displacements to correct the two-hourly GPS positions, and consequently reduced the rms of the estimated displacements on average from 9.3, 3.0 and 2.9 mm to 7.8, 2.8 and 2.8 mm for Up, East and North components, respectively. Therefore, subdaily loading effects due to storm surges should be paid attention to in the GPS positioning that contributes to crustal-motion studies around shallow seas such as the North Sea, the Baltic Sea and the Gulf of Mexico. [less ▲]

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See detailUncertainty of absolute gravity measurements
Van Camp, Michel; Williams, Simon D. P.; Francis, Olivier UL

in Journal of Geophysical Research (2005), 110(B05406), 1-9

Detailed reference viewed: 76 (1 UL)