Consolidating Observation of Land and Sea Level Changes around South Georgia Island

Poster (2019, December 13)

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. Since 2013 the tide gauge at King Edward Point ... [more ▼]

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. Since 2013 the tide gauge at King Edward Point (KEP) with GLOSS ID 187 has been monitored using a GNSS station nearby on Brown Mountain. By accurately geo-referencing the tide gauge and monitoring any vertical land movements, a continuous record of its datum within the Permanent Service for Mean Sea Level (PSMSL) can be established, which in turn makes the recorded and averaged sea levels useful for long-term studies and satellite altimetry calibrations. In 2014 another GNSS station was installed at KEP after local subsidence was sus-pected and later on three additional GNSS stations came to service at the periphery of the main island, making it possible to monitor uplift/subsidence wider afield. Further-more, 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 results from the GNSS and precise levelling meas-urements, and will discuss their impact on the sea level record from the KEP tide gauge and nearby satellite altimetry sea surface heights. This study comes at a timely manner as during the Austral Summer 2019/2020 the jetty will be stabilized and en-larged, and consequently the current tide gauge will be replaced by a new one. Our measurements show that uplift is observed all over South Georgia Island while the ar-ea at KEP and particularly the jetty with tide gauge are subsiding relative to the rest of the island. In contrast, results for the tide gauge record show a lower magnitude of ob-served sea level rise than expected from nearby satellite altimetry. We will revisit all geodetic and oceanic observations in an attempt to improve the agreement between these measurements to summarize the status before the work at the jetty begins. [less ▲]

First Vertical Land Movement Estimates on South Georgia Island: An Impact Study on Sea Level Change from Tide Gauge and Altimetry Measurements

Poster (2017, December 11)

South Georgia Island in the Southern Atlantic Ocean has been a key location for the seismic, geomagnetic and oceanic global monitoring networks. However, no permanent geodetic monitoring station had been ... [more ▼]

South Georgia Island in the Southern Atlantic Ocean has been a key location for the seismic, geomagnetic and oceanic global monitoring networks. However, no permanent geodetic monitoring station had been established there despite the lack of observations from this region within, for example, the International GNSS Service (IGS) network of Global Navigation Satellite System (GNSS) stations. Then, in 2013 the King Edward Point (KEP) Geodetic Observatory was established with a focus on sea level studies and in support of general geoscience applications. Currently, this observatory located roughly half-way along the main island and along its northern coastline, consists of two GNSS stations (KEPA and KRSA) with local benchmark networks, allowing the height determinations from the GNSS antennas to be transferred to the KEP tide gauge (GLOSS ID 187) and forming a height reference within the International Terrestrial Reference Frame. In late 2014, three additional GNSS stations (SG01, SG02 and SG03) were established, all on small islands at the perimeter of the main island. Together the stations provide the best possible opportunity to study various geophysical processes in the region. With the GNSS-derived position time series partly reaching over 4.5 years in length, it has become possible to provide first estimates of vertical land movements for the island and KEP with its surrounding area. Together with four precise levelling campaigns of the benchmark network in 2013, 2014 and two in 2017, it has also been possible to investigate the very local character of the vertical motions, ie. the stability of the jetty upon which the tide gauge is mounted. Our measurements show that while South Georgia Island and the area around KEP are rising, the jetty and tide gauge are subsiding. In this study, we will present the preliminary results from the GNSS and levelling measurements and will discuss their impact on the sea level record from the KEP tide gauge which is ideally situated in a mid-ocean location for satellite altimetry calibration over the Southern Atlantic and Southern Oceans. [less ▲]

Geological interpretation of current subsidence and uplift in the London area, UK, as shown by high precision satellite-based surveying

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 ▲]

Potential Contributions to Geoscience from GNSS Observations of the King Edward Point Geodetic Observatory, South Georgia, South Atlantic Ocean

Poster (2013, September 01)

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’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 will present an evaluation of the GNSS observations from the KEP Geodetic Observatory for the period from February to August 2013. We calculate multipath and positioning statistics and compare these to those from IGS stations. The on-site meteorological data is compared to those from the nearby KEP meteorological station and global numerical weather models, and the impact of these data sets on delay and integrated water vapour estimates will be evaluated. 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 ▲]

Measuring Changes in Ground Level at Tide Gauges using Continuous GPS and Absolute Gravimetry to Improve Estimates of Changes in Sea Level Around Britain

in Proceedings of the 41st Defra Flodd and Coastal Management Conference 2006 (2006)

Researchers studying climate change have used historical tide gauge measurements from all over the world to investigate the changes in sea level that have occurred over the last century or so. However ... [more ▼]

Researchers studying climate change have used historical tide gauge measurements from all over the world to investigate the changes in sea level that have occurred over the last century or so. However, such estimates are a combination of any true sea level variations and any changes in ground level at the specific tide gauge. For a tide gauge record to be used to determine the climate related changes in sea level it is necessary to correct for any changes in ground level. The development in geodetic techniques for monitoring changes in ground level at British tide gauges has been on-going at the IESSG and POL since 1990, based on research funded by both Defra and the Environment Agency. Since 1996, this research has focused on the establishment of continuous GPS (CGPS) stations and the use of absolute gravity (AG), as independent geodetic techniques for measuring changes in ground level. This paper details the results of Defra/EA R&D project FD2319, which is part of the Risk Evaluation and Understanding of Uncertainty Theme. The paper shows how CGPS and AG have been used on a national scale to monitor changes in ground level at tide gauges and obtain estimates of changes in sea level, decoupled from changes in ground level. [less ▲]