References of "Williams, S. D. P"
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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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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 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 detailTrends in UK Mean Sea Level revisited
Woodworth, P.; Teferle, Felix Norman UL; Bingley, R. M. et al

in Geophysical Journal International (2009), 179(179), 19-30

This paper presents estimates of rates of mean sea level (MSL) change around the UK based on a larger tide gauge data set and more accurate analysis methods than have been employed so far. The spatial ... [more ▼]

This paper presents estimates of rates of mean sea level (MSL) change around the UK based on a larger tide gauge data set and more accurate analysis methods than have been employed so far. The spatial variation of the trend in MSL is found to be similar to that inferred from geological information and from advanced geodetic techniques, which is a similar conclusion to that arrived at in previous, less precise and complete studies. The tide gauge MSL trends for 1901 onwards are estimated to be 1.4 +/- 0.2 mm/year larger than those inferred from geology or geodetic methods, suggesting a regional sea level rise of climate change origin several 1/10s mm/year lower than global estimates for the 20th century. However, UK MSL change cannot be described in terms of a simple linear increase alone but includes variations on interannual and decadal timescales. The possible sources of variation in a ‘UK sea level index’ are explored. Air pressure is clearly one such possible source but its direct local forcing through the ‘inverse barometer’ accounts for only one third of the observed variability. A number of larger scale atmospheric and ocean processes must also play important roles, but modelling them satisfactorily and separating the individual contributions presents a major challenge. As regards future regional UK sea level changes, one concludes that there is no basis for major modification to existing projections for the 2080s included in the 2002 UK Climate Impacts Programme studies. [less ▲]

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See detailCrustal Motions in Great-Britain: Evidence from continuous GPS, Absolute Gravity and Holocene Sea-Level Data
Teferle, Felix Norman UL; Bingley, R. M.; Orliac, E. J. et al

in Geophysical Journal International (2009), 178(1), 23-46

Two independent continuous global positioning system (CGPS) processing strategies, based on a double-difference regional network and a globally transformed precise point positioning solution, provide ... [more ▼]

Two independent continuous global positioning system (CGPS) processing strategies, based on a double-difference regional network and a globally transformed precise point positioning solution, provide horizontal and vertical crustal motion estimates for Great Britain. Absolute gravity and geological information from late Holocene sea level data further constrain the vertical motion estimates. For 40 CGPS stations we estimate station velocities and associated uncertainties using maximum likelihood estimation, assuming the presence of white and coloured noise. Horizontal station velocity estimates agree to <1 mm yr−1 between the two CGPS processing strategies and closely follow predicted plate motions. Residual velocities, generally <1 mm yr−1, follow no regular pattern, that is, there is no discernible internal deformation, nor any dependence on station monumentation or time-series length. Vertical station velocity estimates for the two CGPS processing strategies agree to ∼1 mm yr−1, but show an offset of ∼1 mm yr−1 with respect to the absolute gravity (AG) estimates. We attribute this offset to a bias related to known issues in current CGPS results and correct for it by AG-alignment of our CGPS estimates of vertical station velocity. Both CGPS estimates and AG-aligned CGPS estimates of present-day vertical crustal motions confirm the pattern of subsidence and uplift in Great Britain derived from Holocene sea level data for the last few thousand years: ongoing subsidence on Shetland, uplift in most areas of Scotland, and subsidence in large areas of England and Wales. [less ▲]

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See detailA continuous GPS coordinate time series analysis strategy for high-accuracy vertical land movements
Teferle, Felix Norman UL; Williams, S. D. P.; Kierulf, H. P. et al

in Physics and chemistry of the earth (2008), 33(3-4), 205-216

A CGPS coordinate time series analysis strategy was evaluated to determine highly accurate vertical station velocity estimates with realistic uncertainties. This strategy uses a combination of techniques ... [more ▼]

A CGPS coordinate time series analysis strategy was evaluated to determine highly accurate vertical station velocity estimates with realistic uncertainties. This strategy uses a combination of techniques to 1) obtain the most accurate parameter estimates of the station motion model, 2) infer the stochastic properties of the time series in order to compute more realistic error bounds for all parameter estimates, and 3) improve the understanding of apparent common systematic variations in the CGPS coordinate time series, which are believed to be of geophysical and/or technical origin. The strategy provided a pre-processing of the coordinate time series in which outliers and discontinuities were identified. Subsequent parameterization included a mean value, a constant rate, periodic terms with annual and semi-annual frequencies, and offset magnitudes for identified discontinuities. All parameters plus the magnitudes of different stochastic noise were determined using Maximum Likelihood Estimation (MLE). Empirical Orthogonal Function (EOF) analysis was used to study both the temporal and spatial variability of the common modes determined by this technique. After outlining the CGPS coordinate time series analysis strategy this paper shows initial results for coordinate time series for a four year (2000-2003) period from a selection of CGPS stations in Europe that are part of the European Sea Level Service (ESEAS) CGPS network. [less ▲]

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See detailMeasurement of current changes in land levels as input to long-term planning for flood risk management along the Thames estuary
Bingley, R. M.; Teferle, Felix Norman UL; Orliac, E. J. et al

in Journal of Flood Risk Management (2008), 1(3), 162--172

Long-term planning for flood risk management in coastal and estuarine areas requires timely and reliable information on changes in land and sea levels. In this paper we describe how we have produced a ... [more ▼]

Long-term planning for flood risk management in coastal and estuarine areas requires timely and reliable information on changes in land and sea levels. In this paper we describe how we have produced a detailed, high-resolution map of current changes in land levels for the Thames region, and carried out a new assessment of the changes in sea level relative to the land along the Thames Estuary over the past few decades/past century. We conclude the paper by considering the potential benefits of extended monitoring for the long-term planning of flood and coastal defences in that region. [less ▲]

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