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See detailAn Evaluation of the Accuracy of Real-Time Zenith Total Delay Estimates
Ahmed, Furqan UL; Teferle, Felix Norman UL; Bingley, Richard et al

Scientific Conference (2013, April 12)

The continuous evolution of Global Navigation Satellite Systems (GNSS) meteorology has lead to an increased use of associated observations for operational meteorology worldwide. In order to enhance short ... [more ▼]

The continuous evolution of Global Navigation Satellite Systems (GNSS) meteorology has lead to an increased use of associated observations for operational meteorology worldwide. In order to enhance short-term weather forecasts meteorological institutions use modern low-latency Numerical Weather Prediction (NWP) models which assimilate GNSS-derived Zenith Total Delay (ZTD) estimates. For such NWP models a number of GNSS processing strategies allow the provision of these ZTDs with the required accuracy (up to a few millimetres) and latency (hourly). However, meteorological now-casting applications, e.g. for storm tracking, require higher update rates for the ZTDs of 10 or even 5 min, which can be achieved, but only at a loss in accuracy. Using the IGS Real-Time Service orbit and clock products together with an appropriate GNSS software, it is possible to estimate the ZTDs in real-time. Available software packages either use GNSS processing strategies based on differenced or un-differenced observations, such as Precise Point Positioning (PPP). While PPP has clear advantages for efficiently processing data streams from large GNSS networks this strategy is more affected by inaccuracies in the real-time products than when using differenced observations. On the other hand, recent advances in PPP integer ambiguity resolution nowadays provide this strategy with the benefits of ambiguity-fixed solutions. In this study, we present an evaluation of the accuracy of real-time ZTD estimates obtained from several GNSS processing systems through comparison to those obtained from a near real-time and a post-processing system. [less ▲]

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See detailA Bayesian Monte Carlo Markov Chain Method for the Analysis of GPS Position Time Series
Olivares Pulido, German UL; Teferle, Felix Norman UL

Poster (2013, April 12)

Position time series from continuous GPS are an essential tool in many areas of the geosciences and are, for example, used to quantify long-term movements due to processes such as plate tectonics or ... [more ▼]

Position time series from continuous GPS are an essential tool in many areas of the geosciences and are, for example, used to quantify long-term movements due to processes such as plate tectonics or glacial isostatic adjustment. It is now widely established that the stochastic properties of the time series do not follow a random behavior and this affects parameter estimates and associated uncertainties. Consequently, a comprehensive knowledge of the stochastic character of the position time series is crucial in order to obtain realistic error bounds and for this a number of methods have already been applied successfully. We present a new Bayesian Monte Carlo Markov Chain (MCMC) method to simultaneously estimate the model and the stochastic parameters of the noise in GPS position time series. This method provides a sample of the likelihood function and thereby, using Monte Carlo integration, all parameters and their uncertainties are estimated simultaneously. One advantage of the MCMC method is that the computational time increases linearly with the number of parameters, hence being very suitable for dealing with a high number of parameters. A second advantage is that the properties of the estimator used in this method do not depend on the stationarity of the time series. At least on a theoretical level, no other estimator has been shown to have this feature. Furthermore, the MCMC method provides a means to detect multi-modality of the parameter estimates. We present an evaluation of the new MCMC method through comparison with widely used optimization and empirical methods for the analysis of GPS position time series. [less ▲]

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See detailDetecting offsets in GPS time series: First results from the detection of offsets in GPS experiment
Gazeaux, Julien; Williams, Simon; King, Matt et al

in Journal of Geophysical Research. Solid Earth (2013), 118

The accuracy of Global Positioning System (GPS) time series is degraded by the presence of offsets. If these are not detected and adjusted correctly they bias velocities, and hence geophysical estimates ... [more ▼]

The accuracy of Global Positioning System (GPS) time series is degraded by the presence of offsets. If these are not detected and adjusted correctly they bias velocities, and hence geophysical estimates, and degrade the terrestrial reference frame. They also alter apparent time series noise characteristics as undetected offsets resemble a random walk process. As such, offsets are a substantial problem. A number of offset detection methods have been developed across a range of fields, and some of these are now being tested in geodetic time series. The DOGEx (Detection of Offsets in GPS Experiment) project aims to test the effectiveness of automated and manual offset detection approaches and the subsequent effect on GPS-derived velocities. To do this, simulated time series were first generated that mimicked realistic GPS data consisting of a velocity component, offsets, white and flicker noises (1/f spectrum noises) composed in an additive model. We focus on offset detection and together with velocity biases induced by incorrect offset detection. We show that, at present, manual methods (where offsets are hand -picked by GPS time series experts) almost always give better results than automated or semi-automated methods (two automated methods give quite similar velocity bias as the best manual solutions). For instance, the 5th percentile ranges (5% to 95%) in velocity bias for automated approaches is equal to 4.2mm/year,whereas it is equal to 1.8mm/yr for the manual solutions. However the True Positive detection rate of automated solutions is significantly higher than those for the manual solutions, being around 37% for the best automated, and 42% for the best manual solution. The amplitude of offsets detectable by automated solutions is greater than for hand picked solutions, with the smallest detectable offset for the two best manual solutions equal to 5mm and 7mm and to 8mm and 10mm for the two best automated solutions. The best manual solutions yielded velocity biases from the truth commonly in the range ±0.2mm/yr, whereas the best automated solutions produced biases no better than double this range. Assuming the simulated time series noise levels continue to be representative of real GPS time series, robust geophysical interpretation of individual site velocities lower than these levels is therefore not robust. Further work is required before we can routinely interpret sub-mm/yr velocities for single GPS stations. [less ▲]

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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

Scientific Conference (2013)

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

In 2013 the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring (TIGA) Working Group started their reprocessing campaign which proposes to re-analyse 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 detailThe King Edward Point Geodetic Observatory
Teferle, Felix Norman UL

Report (2013)

During the period from 7th until 14th February 2013 Norman Teferle (University of Luxembourg) and Seth White (Unavco Inc.) visited King Edward Point (KEP) research station, South Georgia, to establish the ... [more ▼]

During the period from 7th until 14th February 2013 Norman Teferle (University of Luxembourg) and Seth White (Unavco Inc.) visited King Edward Point (KEP) research station, South Georgia, to establish the KEP Geodetic Observatory (KEPGO). The observatory consists of an autonomous, continuous Global Navigation Satellite System (GNSS) station with auxiliary equipment on Brown Mountain, as well as, benchmarks on Brown Mountain and at KEP research station. The primary objective of the observatory is to measure vertical land movements in order to study sea level changes using the KEP tide gauge record or satellite altimeter data. Therefore, the existing tide gauge was connected to the observatory through precise levelling and campaign GNSS observations. The levelling was carried out over the tide gauge itself, two existing United Kingdom Hydrographic Office (UKHO) and four newly established KEPGO tide gauge benchmarks (TGBMs). The GNSS observations were carried out on two benchmarks and their coordinates were computed with respect to the continuous GNSS station on Brown Mountain. Taking the UKHO height information together with the levelling and GNSS results it is suggested that the UKHO TGBM on the jetty may have settled by a few centimetres over the period from 2003 to 2013 and that the UKHO height datum requires a shift of by about -1 m in order to bring it closer to a globally consistent vertical reference system. This technical report details the installation work and analysis carried out during and after the visit. [less ▲]

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See detailA Bayesian Monte Carlo Markov Chain Method for Parameter Estimation of Fractional Differenced Gaussian Processes
Olivares Pulido, German UL; Teferle, Felix Norman UL

in IEEE Transactions on Signal Processing (2013), 61(9), 2405-2412

We present a Bayesian Monte Carlo Markov Chain method to simultaneously estimate the spectral index and power amplitude of a fractional differenced Gaussian process at low frequency, in presence of white ... [more ▼]

We present a Bayesian Monte Carlo Markov Chain method to simultaneously estimate the spectral index and power amplitude of a fractional differenced Gaussian process at low frequency, in presence of white noise, and a linear trend and periodic signals. This method provides a sample of the likelihood function and thereby, using Monte Carlo integration, all parameters and their uncertainties are estimated simultaneously. We test this method with simulated and real Global Positioning System height time series and propose it as an alternative to optimization methods currently in use. Furthermore, without any mathematical proof, the results from the simulations suggest that this method is unaffected by the stationary regime and hence, can be used to check whether or not a time series is stationary. [less ▲]

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See detailAn Evaluation of Real-Time Zenith Total Delay Estimates
Ahmed, Furqan UL; Teferle, Felix Norman UL; Bingley, Richard

Poster (2012, December)

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See detailGNSS Meteorology in Luxembourg
Ahmed, Furqan UL; Teferle, Felix Norman UL; Bingley, Richard et al

in Cahier Scientifique - Revue Technique Luxembourgeoise (2012), (1), 16-22

Atmospheric water vapour is a primary greenhouse gas and plays an important role in weather forecasting and climate monitoring. Global Navigation Satellite System (GNSS) signals experience a propagation ... [more ▼]

Atmospheric water vapour is a primary greenhouse gas and plays an important role in weather forecasting and climate monitoring. Global Navigation Satellite System (GNSS) signals experience a propagation delay, which is related to the amount of water vapour in the lower atmosphere. Hence GNSS observations can be processed to estimate this delay with millimetre-level accuracy and together with meteorological data can be used to compute the amount of atmospheric water vapour on various temporal and spatial scales. [less ▲]

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See detailFirst Zenith Total Delay and Integrated Water Vapour Estimates from the Near Real-Time GNSS Data Processing Systems at the University of Luxembourg
Ahmed, Furqan UL; Teferle, Felix Norman UL; Bingley, Richard

Poster (2012, March 16)

Since June 2011, the University of Luxembourg has started in collaboration with the University of Nottingham a PhD project entitled “The Potential of Precipitable Water Vapour Measurements using Global ... [more ▼]

Since June 2011, the University of Luxembourg has started in collaboration with the University of Nottingham a PhD project entitled “The Potential of Precipitable Water Vapour Measurements using Global Navigation Satellite Systems in Luxembourg (PWVLUX)”, which is funded by the Fonds National de la Recherche (FNR) Luxembourg. The research objectives of the project are to study the potential for improvements in short-term weather forecasts and long-term climate variability for Luxembourg and the Greater Region by inclusion of the observations from Global Navigation Satellite Systems (GNSS) in the existing techniques. To achieve the research objectives, systems are being set up at the University of Luxembourg which process ground-based GNSS data for the provision of zenith total delay (ZTD) and integrated water vapour (IWV) estimates in real-time, near real-time and post-processing modes. Through collaboration with the Administration du cadastre et de la topographie (Luxembourg) and the Service public de Wallonie (Belgium), the coverage of the available GNSS permanent networks is improved over the primary project area, although also data from other European and global networks are processed. The meteorological analysis of the PWVLUX products is supported through collaborations with the Meteorological Service of the Administration de la navigation aérienne and the EUMETNET project E-GVAP. In this study we present the first ZTD and IWV estimates obtained from the near-real time processing systems in development at the University of Luxembourg. In a preliminary evaluation we compared their performance to some state-of-the-art systems already in operation and found that the ZTD estimates agree up to a few millimeters and the IWV estimates agree at the sub-millimeter level. [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 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 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 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 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 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 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 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 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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