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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 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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See detailKinematic precise point postioning at remote marine platforms
Geng, J.; Teferle, Felix Norman UL; Meng, X. et al

in GPS Solutions (2010), 14(4), 343-350

Precise kinematic differential positioning using the global positioning system (GPS) at a marine platform usually requires a relatively short distance (e.g. 500km) to a land-based reference station. As an ... [more ▼]

Precise kinematic differential positioning using the global positioning system (GPS) at a marine platform usually requires a relatively short distance (e.g. 500km) to a land-based reference station. As an alternative, precise point positioning (PPP) is normally considered free from this limiting requirement. However, due to the prerequisite of network-based satellite products, PPP at a remote marine platform may still be affected by its distance to the reference network. Hence, this paper investigates this scenario by configuring rings of reference stations with different radii centered on a to-be-positioned marine platform. Particularly, we applied ambiguity resolution at a single station to PPP by estimating uncalibrated phase delays (UPDs). We used three rings of reference stations centered on a vessel, with radii of roughly 900, 2,000 and 3,600 km, to determine satellite clocks and UPDs independently. For comparison, we also performed differential positioning based on a single reference station with baseline lengths of about 400, 1,700 and 2,800 km. We demonstrate that, despite the increasing ring-network radius to a few 1,000 km, the overall change in accuracy of the satellite clocks that are used at the vessel is smaller than 0.02 ns, and the RMS values of differences between the three sets of narrow-lane UPD estimates are around 0.05 cycles only. Moreover, the kinematic positioning accuracy of PPP is affected by the increasing ring-network radius, but can still achieve several centimeters after ambiguity resolution when the vessel is over a few 1,000 km away from the ring network, showing better performance than that of differential positioning. Therefore, we propose that ambiguity- fixed PPP can be used at remote marine platforms that support precise oceanographic and geophysical applications in open oceans. [less ▲]

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See detailPerformance of Precise Point Positioning with Ambiguity Resolution for 1- to 4- hour Observation Periods
Geng, J.; Meng, X.; Teferle, Felix Norman UL et al

in Survey Review (2010), 42(316), 155-165

Recent progress in integer ambiguity resolution at a single station has made it possible to achieve high positioning accuracy in static precise point positioning (PPP) using a short period of observations ... [more ▼]

Recent progress in integer ambiguity resolution at a single station has made it possible to achieve high positioning accuracy in static precise point positioning (PPP) using a short period of observations. In this paper, 12 stations across Europe are used to conduct short-period (i.e. one, two, three and four hours) static PPP with ambiguity resolution from Day 245 to 251 in 2007. It is demonstrated that, when over three hours of observations are used, PPP can achieve a success rate of 100% for ambiguity resolution, a 3D positioning accuracy of about 1.0 cm and an occurrence of less than 1.0% for degraded solutions. Moreover, for the fixed solutions, increasing the observation period hardly improves the horizontal positioning accuracy while still improving the vertical one. Therefore, it is proposed that at least three hours of observations should be used in the ambiguity-fixed static PPP if a reliable millimetre positioning accuracy is required in the engineering applications. [less ▲]

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See detailTowards PPP-RTK: Ambiguity Resolution in Real-Time Precise Point Positioning
Geng, J.; Teferle, Felix Norman UL; Meng, X. et al

in Advances in Space Research (2010)

Integer ambiguity resolution at a single station can be achieved by introducing predetermined uncalibrated phase delays (UPDs) into the float ambiguity estimates of precise point positioning (PPP). This ... [more ▼]

Integer ambiguity resolution at a single station can be achieved by introducing predetermined uncalibrated phase delays (UPDs) into the float ambiguity estimates of precise point positioning (PPP). This integer resolution technique has the potential of leading to a PPP-RTK (Real-Time Kinematic) model where PPP provides rapid convergence to a reliable centimeter-level positioning accuracy based on an RTK reference network. Nonetheless, implementing this model is technically subject to how rapidly we can fix wide-lane ambiguities, stabilize narrow-lane UPD estimates, and achieve the first ambiguity-fixed solution. To investigate these issues, we used seven days of 1-Hz sampling GPS data at 91 stations across Europe. We find that at least 10 minutes of observations are required for most receiver types to reliably fix about 90% of wide-lane ambiguities corresponding to high elevations, and over 20 minutes to fix about 90% of those corresponding to low elevations. Moreover, several tens of minutes are usually required for a regional network before a narrow-lane UPD estimate stabilizes to an accuracy of far better than 0.1 cycles. Finally, for hourly data, ambiguity resolution can significantly improve the accuracy of epoch-wise position estimates from 13.7, 7.1 and 11.4 cm to 0.8, 0.9 and 2.5 cm for the East, North and Up components, respectively, but a few tens of minutes is required to achieve the first ambiguity-fixed solution. Therefore, from the timeliness aspect, our PPP-RTK model currently cannot satisfy the critical requirement of instantaneous precise positioning where ambiguity-fixed solutions have to be achieved within at most a few seconds. However, this model can still be potentially applied to some near-real-time remote sensing applications, such as the GPS meteorology. [less ▲]

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See detailInteger ambiguity resolution in precise point poistioning: method comparison
Geng, J.; Meng, Xiaolin; Dodson, Alan H et al

in Journal of Geodesy (2010), 84(9), 569-581

Integer ambiguity resolution at a single receiver can be implemented by applying improved satellite products where the fractional-cycle biases (FCBs) have been separated from the integer ambiguities in a ... [more ▼]

Integer ambiguity resolution at a single receiver can be implemented by applying improved satellite products where the fractional-cycle biases (FCBs) have been separated from the integer ambiguities in a network solution. One method to achieve these products is to estimate the FCBs by averaging the fractional parts of the float ambiguity estimates, and the other is to estimate the integer-recovery clocks by fixing the undifferenced ambiguities to integers in advance. In this paper, we theoretically prove the equivalence of the ambiguity-fixed position estimates derived from these two methods by assuming that the FCBs are hardware-dependent and only they are assimilated into the clocks and ambiguities. To verify this equivalence, we implement both methods in the Position and Navigation Data Analyst software to process 1 year of GPS data from a global network of about 350 stations. The mean biases between all daily position estimates derived from these two methods are only 0.2, 0.1 and 0.0 mm, whereas the standard deviations of all position differences are only 1.3, 0.8 and 2.0 mm for the East, North and Up components, respectively. Moreover, the differences of the position repeatabilities are below 0.2 mm on average for all three components. The RMS of the position estimates minus those from the International GNSS Service weekly solutions for the former method differs by below 0.1 mm on average for each component from that for the latter method. Therefore, considering the recognized millimeter-level precision of current GPS-derived daily positions, these statistics empirically demonstrate the theoretical equivalence of the ambiguity-fixed position estimates derived from these two methods. In practice, we note that the former method is compatible with current official clock-generation methods, whereas the latter method is not, but can potentially lead to slightly better positioning quality. [less ▲]

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See detailRapid re-convergences to ambiguity-fixed solutions in precise point-positioning
Geng, J.; Meng, X.; Dodson, A. H. et al

in Journal of Geodesy (2010), 84(12), 705-714

Integer ambiguity resolution at a single station can be preformed if the fractional-cycle biases are separated from the ambiguity estimates in precise point positioning (PPP). Despite the improved ... [more ▼]

Integer ambiguity resolution at a single station can be preformed if the fractional-cycle biases are separated from the ambiguity estimates in precise point positioning (PPP). Despite the improved positioning accuracy by such integer resolutions, the convergence to an ambiguity-fixed solution normally requires at least a few tens of minutes. More importantly, such convergences can repeatedly occur on the occasion of losses of tracking locks for many satellites if an open sky-view is not constantly available, consequently totally destroying the practicability of real-time PPP. In this study, in case of such re-convergences, we develop a method in which ionospheric delays are precisely predicted to significantly accelerate integer ambiguity resolutions. The effectiveness of this method consists in two aspects: First, wide-lane ambiguities can be rapidly resolved using the ionosphere- corrected wide-lane measurements, instead of the noisy Melbourne-Wübbena combination measurements; second, narrow-lane ambiguity resolution can be accelerated under the tight constraints derived from the ionosphere-corrected unambiguous wide-lane measurements. In the tests at 90 static stations suffering from simulated total loss of tracking locks, 93.3% and 95.0% of re- convergences to wide-lane and narrow-lane ambiguity resolutions can be achieved within 5 s, respectively, even though the time latency for the predicted ionospheric delays is up to 180 s. In the tests at a mobile van moving in a GPS-adverse environment where satellite number significantly decreases and cycle slips frequently occur, only when the predicted ionospheric delays are applied can the rate of ambiguity-fixed epochs be dramatically improved from 7.7% to 93.6% of all epochs. Therefore, this method can potentially relieve the unrealistic requirement of a continuous open sky- view by most PPP applications and improve the practicability of real-time PPP. [less ▲]

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See detailAmbiguity resolution in precise point positioning with hourly data
Geng, J.; Teferle, Felix Norman UL; Shi, C. et al

in GPS Solutions (2009), 13(4), 263-270

Precise Point Positioning (PPP) has become a recognized and powerful tool for scientific analysis of Global Positioning System (GPS) measurements. Until recently, ambiguity resolution at a single station ... [more ▼]

Precise Point Positioning (PPP) has become a recognized and powerful tool for scientific analysis of Global Positioning System (GPS) measurements. Until recently, ambiguity resolution at a single station has been considered difficult, due to the non-integer uncalibrated hardware delays (UHD) originating in receivers and satellites. Fortunately, recent studies show that if these UHD can be determined precisely with a network in advance, then ambiguity resolution at a single station is possible. In this study, the method proposed by Ge et al (2007) is adopted with a refinement in which the fractional parts of single-difference narrow-lane UHD for a satellite pair are determined within each full pass over a regional network. This study uses the European Reference Frame Permanent Network (EPN) to determine these UHD from Day 245 to 251 in 2007, and 27 IGS stations inside and outside the EPN are used to conduct ambiguity resolution in hourly PPP. It is found that the total hourly position accuracy is improved from 3.8 cm, 1.5 cm and 2.8 cm to 0.5 cm, 0.5 cm and 1.4 cm in East, North and Up, respectively, for the stations inside the EPN. For the stations outside the EPN, some of which are even over 2000 km away from the EPN, their total hourly East, North and Up position accuracies still achieve 0.6 cm, 0.6 cm and 2.0 cm, respectively, when the EPN-based UHD are applied to the ambiguity resolution at these stations. Therefore, it is feasible and beneficial for the operators of GPS networks, such as the providers of PPP-based online services, to provide these UHD estimates as an additional product to allow users to conduct ambiguity resolution in PPP. [less ▲]

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See detailGlacial Isostatic Adjustment of the British Isles: New constraints form GPS measurements of crustal motion
Bradley, S. L.; Milne, G. A.; Teferle, Felix Norman UL et al

in Geophysical Journal International (2009), 178(178), 14-22

We compared estimates of crustal velocities within Great Britain based on continuous global positioning system (CGPS) measurements to predictions from a model of glacial isostatic adjustment (GIA). The ... [more ▼]

We compared estimates of crustal velocities within Great Britain based on continuous global positioning system (CGPS) measurements to predictions from a model of glacial isostatic adjustment (GIA). The observed and predicted values for vertical motion are highly correlated indicating that GIA is the dominant geodynamic process contributing to this field. In contrast, motion of the Eurasian plate dominates the horizontal motion component. A model of plate motion was adopted to remove this signal in order to estimate intraplate horizontal motion associated with GIA. However, a coherent pattern of horizontal motion was not evident in the resulting velocity field. We adopted a recently published model of the British–Irish ice sheet to predict vertical crustal motion for a large number of spherically symmetric Earth viscosity models. Our results show that the adopted ice model is capable of producing a high-quality fit to the observations. The CGPS-derived estimates of vertical motion provide a useful constraint on the average value of viscosity within the upper mantle. Values of model lithospheric thickness and lower mantle viscosity are less well resolved, however. A suite of predictions based on an alternative ice model indicates that the vertical motion data are relatively insensitive to uncertainties in the ice loading history and so the constraints on upper mantle viscosity are robust. [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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See detailA GPS Network Densification in Saudi Arabia in Support of Geophysical Investigations in the Region
Almuslmani, Bandar; Al-Motari, Eid; Bingley, Richard M. et al

Poster (2006)

Current investigations of the motions of the Arabian and its neighboring plates are primarily based on GPS measurements obtained in the surrounding areas of the Arabian plate, with few stations actually ... [more ▼]

Current investigations of the motions of the Arabian and its neighboring plates are primarily based on GPS measurements obtained in the surrounding areas of the Arabian plate, with few stations actually located on the Arabian plate itself in the Kingdom of Saudi Arabia. In order to advance the knowledge of the dynamics of the Arabian plate and its intra-plate deformations, the General Directorate of Military Survey (GDMS), through a collaboration with the Institute of Engineering Surveying and Space Geodesy (IESSG), densified the GPS network in Saudi Arabia, covering nearly two thirds of the tectonic plate. Since July 2002, a network of 32 GPS stations has been established at locations of the Saudi Arabia geodetic network. At all of these GPS stations a concrete pillar has been used as the monument and the locations have been selected in order to give the broadest distribution of observing sites. During 2005, 27 additional GPS stations in the Hejaz and Asser Mountains in the south-western part of Saudi Arabia, have been established, with the GDMS GPS network now comprising a total of 59 stations. In this presentation we will introduce the new GPS network in Saudi Arabia established by GDMS and will present the initial results from campaigns in March 2003 and March 2005. We show preliminary estimates of absolute and relative Arabian plate motions inferred from the GPS network and a detailed comparison of the results based on the Bernese GPS software versions 4.2 and 5.0. [less ▲]

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See detailMeasuring Changes in Ground Level at Tide Gauges using Continuous GPS and Absolute Gravimetry to Improve Estimates of Changes in Sea Level Around Britain
Bingley, Richard M; Teferle, Felix Norman UL; Dodson, Alan H et al

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 ▲]

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See detailThe Effect of Processing Technique and Reference Frame Definition on Noise in CGPS Position Time Series
Teferle, Felix Norman UL; Williams, Simon; Kierulf, Halfdan et al

Poster (2005)

In this presentation we investigate the effects of GPS processing techniques and strategies, and the related reference frame realization, on the stochastic properties of continuous GPS (CGPS) position ... [more ▼]

In this presentation we investigate the effects of GPS processing techniques and strategies, and the related reference frame realization, on the stochastic properties of continuous GPS (CGPS) position time series. It was of particular interest to establish whether and how different GPS processing techniques and strategies, e.g. double differencing (DD) and precise point positioning (PPP), and the use of different orbit and clock products, and/or the definition of the reference frame (partly dependent on the applied strategy) affect the colored noise content of time series. We used CGPS position time series from 15 different solutions obtained from seven different analysis centers as part of the European Sea Level Service - Research Infrastructure project (ESEAS-RI) using the GIPSY OASIS II, GAMIT and Bernese GPS softwares. All time series analyzed have at least three years of data for the period between 2000 and 2005. Furthermore, a selected set of position time series was also analyzed using Empirical Orthogonal Function (EOF) analysis. The noise content of the first 15 modes, representing the solution-specific common mode time series for each of the selected solutions were then also investigated for colored noise. Using Maximum Likelihood Estimation (MLE) a white, a white plus flicker, a white plus power- law and a white plus first-order Gauss-Markov (FOGM) noise model were fitted to the position and EOF time series data. For both the position and EOF time series the parameter model included a constant, a rate and harmonic terms with annual, semi-annual, 4- monthly, 3-monthly, 2.4-monthly and 13.66 day periods. Position jumps were modeled at logged epochs or at visible discontinuities in the time series. The MLE showed that in most cases the best fitting noise model is a combination of white plus power-law noise with average spectral indices in the range between -0.5 and -1.4. This model is closely followed by the combination of white plus flicker and white plus FOGM noise. The noise properties of the EOF time series follow predominantly a white plus power-law character, with the first few modes indicating a white plus flicker noise behavior. In general, DD solutions contain less noise than PPP solutions and that regional reference frame definitions further reduce the amount of noise in the time series. [less ▲]

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