The King Edward Point Geodetic Observatory, South Georgia, South Atlantic Ocean: A First Evaluation and Potential Contributions to Geosciences

in Willis, Pascal; Rizos, Chris (Eds.) IAG 150 Years Proceedings of the 2013 IAG Scientific Assembly, Postdam, Germany, 1–6 September, 2013 (2016)

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 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 tectonic plate, South Georgia Island has been a key location for a number of global monitoring networks, e.g. seismic, geomagnetic and oceanic. However, no permanent geodetic monitoring station has been established previously, despite the lack of observations from this region. In this study we will present an evaluation of the GNSS and meteorological observations from the KEP Geodetic Observatory for the period from 14 February to 31 December 2013. We calculate multipath and positioning statistics and compare these to those from IGS stations using equipment of the same type. The on-site meteorological data are compared to those from the nearby KEP meteorological station and the NCEP/NCAR reanalysis model, and the impact of these data sets on integrated water vapour estimates is evaluated. We 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 ▲]

An evaluation of multi-GNSS zenith tropospheric delay products based on real-time satellite products

Poster (2015, October)

The Potential of Precipitable Water Vapour Measurements from Global Navigation Satellite Systems in Luxembourg

Doctoral thesis (2015)

The primary objectives of this research were to investigate the potential of precipitable water vapour (PWV) estimates derived from Global Navigation Satellite Systems (GNSS) measurements, firstly, for ... [more ▼]

The primary objectives of this research were to investigate the potential of precipitable water vapour (PWV) estimates derived from Global Navigation Satellite Systems (GNSS) measurements, firstly, for short-term weather forecasting based on numerical weather prediction (NWP) in Luxembourg and its surroundings and, secondly, for monitoring climate on regional and global scales. The suitability of real-time (RT) zenith total delay (ZTD) estimates obtained from three different precise point positioning (PPP) software packages was assessed by comparing them with the state-of-the-art product from the International GNSS Service (namely the IGS Final troposphere product) as well as collocated radiosonde (RS) observations. It was found that the RT-PPP ZTD estimates from two of the three software packages meet the threshold requirements for NWP nowcasting. The biases between the RT-PPP ZTD and the reference ZTD were found to be stable over time for all the RT-PPP ZTD solutions. A millimetre-level impact on the RT-PPP ZTD estimates was also observed when integer ambiguities were resolved. The impact of assimilating GNSS-derived near real-time (NRT) ZTD in the Applications of Research to Operations at Mesoscale (AROME) NWP model using a three-dimensional, variational (3D-VAR) assimilation scheme on the quality of weather forecasts for Luxembourg was studied. It was found that the assimilation of GNSS-derived ZTD systematically improves the atmospheric humidity short-range forecasts in comparison to other water vapour observing systems (radio soundings, satellite radiances, surface networks). Examination of several case studies revealed the ability of the ZTD observations to modify the intensity and location of predicted precipitation in accordance with previous studies. The addition of ZTD from the dense GNSS network in Wallonie (Belgium) was also found to be beneficial by improving the prediction of rainfall patterns in Luxembourg. The 2D maps of IWV obtained from the hourly NRT system were compared with cloud distribution and precipitation maps from satellite and weather radar data, respectively, and a good agreement in the location of the front system was found. A rise in IWV was recorded during a precipitation event in Luxembourg and it was shown that by observing the IWV change over the ground-based GNSS stations in Luxembourg in NRT, it is possible to determine the speed and direction of the passing fronts and hence storms can also be tracked. A 5-year long global reprocessed GNSS data set containing over 400 ground-based GNSS stations and based on the double differencing strategy has been used to validate the ZTD estimates obtained from the climate reanalysis model of the European Centre for Medium-range Weather Forecasts (ECMWF) namely the ECMWF ReAnalysis-Interim (ERA-Interim) in different climate zones. It was found that the correlation coefficient between the GNSS-derived ZTD observations and the ZTD modeled by ERA-Interim ranges from 0.87 to 1.00. Higher correlation coefficients were found for the stations belonging to the climate zones with lower amount of water vapour. Furthermore, it was found that the mean, SDev and RMS of the differences depends on periodicity in the residuals, altitude of the stations in a particular zone as well as the topographic variation in the zone. Monthly and seasonal means of GNSS-derived ZTD (ZTDgnss) were computed using a global ZTDgnss dataset consisting of 19-years of data and over 400 stations to study the climate variability in different climate zones. In terms of seasonal means, it was found that the climate zones in the northern hemisphere have ZTD maxima in Boreal Summer (June-July-August) whereas those in the southern hemisphere have ZTD maxima in Austral Summer (December-January-February). Monthly and seasonal variability in ZTDgnss was also studied for the locations of 6 ground-based GNSS (SPSLux) stations in Luxembourg. It was found that all the 6 SPSLux stations experience the same monthly and seasonal variability of ZTDgnss. In terms of monthly variation, it was found that the maxima in ZTDgnss occurs around the month of July for all the 6 SPSLux stations whereas in terms of seasonal variation, the location of maxima was found to be in Summer (June-July-August). The suitability of the ZTD derived using precise point positioning (PPP) strategy for climate monitoring applications was studied through its comparison with the ZTD estimates derived using double differenced positioning (DDP) using a global network of 114 stations and duration of 1 year. The mean differences between the two were found to be ranging from -3.35 to 2.37 mm over different climate zones. Furthermore, correlation coefficients ranging from 0.90 and 1.00 were found between the ZTD obtained using the two processing strategies. It was found that use of higher elevation cut-off angles and tropospheric mapping functions based on NWP improves the agreement between the PPP and DDP solutions. [less ▲]

Assimilation of zenith total delays in the AROME France convective scale model: a recent assessment

in Tellus. Series A (2015)

Comparative Analysis of Real-Time Precise Point Positioning Zenith Total Delay Estimates

in GPS Solutions (2014)

The continuous evolution of global navigation satellite systems (GNSS) meteorology has led to an increased use of associated observations for operational modern low-latency numerical weather prediction ... [more ▼]

The continuous evolution of global navigation satellite systems (GNSS) meteorology has led to an increased use of associated observations for operational modern low-latency numerical weather prediction (NWP) models, which assimilate GNSS-derived zenith total delay (ZTD) estimates. The development of NWP models with faster assimilation cycles, e.g., 1-h assimilation cycle in the rapid update cycle NWP model, has increased the interest of the meteorological community toward sub-hour ZTD estimates. The suitability of real-time ZTD estimates obtained from three different precise point positioning software packages has been assessed by comparing them with the state-of-the-art IGS final troposphere product as well as collocated radiosonde (RS) observations. The ZTD estimates obtained by BNC2.7 show a mean bias of 0.21 cm, and those obtained by the G-Nut/Tefnut software library show a mean bias of 1.09 cm to the IGS final troposphere product. In comparison with the RS-based ZTD, the BNC2.7 solutions show mean biases between 1 and 2 cm, whereas the G-Nut/Tefnut solutions show mean biases between 2 and 3 cm with the RS-based ZTD, and the ambiguity float and ambiguity fixed solutions obtained by PPPWizard have mean biases between 6 and 7 cm with the references. The large biases in the time series from PPP-Wizard are due to the fact that this software has been developed for kinematic applications and hence does not apply receiver antenna eccentricity and phase center offset (PCO) corrections on the observations. Application of the eccentricity and PCO corrections to the a priori coordinates has resulted in a 66 % reduction of bias in the PPP-Wizard solutions. The biases are found to be stable over the whole period of the comparison, which are criteria (rather than the magnitude of the bias) for the suitability of ZTD estimates for use in NWP nowcasting. A millimeter-level impact on the ZTD estimates has also been observed in relation to ambiguity resolution. As a result of a comparison with the established user requirements for NWP nowcasting, it was found that both the GNut/Tefnut solutions and one of the BNC2.7 solutions meet the threshold requirements, whereas one of the BNC2.7 solution and both the PPPWizard solutions currently exceed this threshold. [less ▲]

Comparative Analysis of Real-Time Precise Point Positioning Zenith Total Delay Estimates

Poster (2013, December 13)

The use of observations from Global Navigation Satellite Systems (GNSS) in operational meteorology is increasing worldwide due to the continuous evolution of GNSS. The assimilation of near real-time (NRT ... [more ▼]

The use of observations from Global Navigation Satellite Systems (GNSS) in operational meteorology is increasing worldwide due to the continuous evolution of GNSS. The assimilation of near real-time (NRT) GNSS-derived zenith total delay (ZTD) estimates into local, regional and global scale numerical weather prediction (NWP) models is now in operation at a number of meteorological institutions. The development of NWP models with high update cycles for nowcasting and monitoring of extreme weather events in recent years, requires the estimation of ZTD with minimal latencies, i.e. from 5 to 10 minutes, while maintaining an adequate level of accuracy for these. The availability of real-time (RT) observations and products from the IGS RT service and associated analysis centers make it possible to compute precise point positioning (PPP) solutions in RT, which provide ZTD along with position estimates. This study presents a comparison of the RT ZTD estimates from three different PPP software packages (G-Nut/Tefnut, BNC2.7 and PPP-Wizard) to the state-of-the-art IGS Final Troposphere Product employing PPP in the Bernese GPS Software. Overall, the ZTD time series obtained by the software packages agree fairly well with the estimates following the variations of the other solutions, but showing various biases with the reference. After correction of these the RMS differences are at the order of 0.01 m. The application of PPP ambiguity resolution in one solution or the use of different RT product streams shows little impact on the ZTD estimates. [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 ▲]

Installation and First Evaluation of the King Edward Point Geodetic Observatory, South Georgia

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 ▲]

An Evaluation of Real-Time Zenith Total Delay Estimates

Poster (2012, December)

An Evaluation of Real-Time, Near Real-Time and Post-Processed Zenith Total Delay Estimates

Poster (2012, July)