Papers by Felicia N R Teferle
On the Impact of GNSS Multipath Correction Maps on Slant Wet Delays for Tracking Severe Weather Events
<p>Climate change has led to an increase in the frequency and severity of w... more <p>Climate change has led to an increase in the frequency and severity of weather events with intense precipitation and subsequently a greater susceptibility to flash flooding of cities worldwide. As a result, accurate fore- and now-casting of imminent extreme precipitation has become critical for the warning and mitigation of these hydro-meteorological hazards. Networks of ground-based Global Navigation Satellite System (GNSS) stations enable the measurement of integrated water vapour along slant pathways, providing three-dimensional (3D) water vapour distributions at low cost and in real-time. This makes these data a valuable complementary source of information for tracking storm events and predicting their paths. However, it is well established that multipath effects at GNSS stations do impact incoming signals, especially at low elevations. While the GNSS products for meteorology to date consist predominantly of estimates of zenith total delay and horizontal gradients, these products are not optimal for constraining the 3D distribution of water vapour above a station. The direct use of slant delays counteracts this lack of azimuthal information but is more susceptible to multipath errors at low elevations. This study investigates the impact of multipath-corrected slant wet delay (SWD) estimates on tracking extreme weather events using the convective storm event over Bulgaria, Greece and Turkey on July 27, 2017, which resulted in flash floods and significant property damage. First, we recovered the one-way SWD by adding GNSS post-fit phase residuals, representing the non-isotropic component of the SWD, i.e., the higher-order inhomogeneity. As the MP errors in the GNSS phase observables can significantly affect the SWD from individual satellites, we employed an averaging strategy for stacking the post-fit phase residuals obtained from our Precise Point Positioning (PPP) processing strategy to generate station-specific MP correction maps. The spatial stacking was carried out in congruent cells with an optimal resolution in elevation and azimuth at the local horizon but with decreasing azimuth resolution as the elevation angle increases. This permits an approximately equal number of observations allocated to each cell. Using these MP correction maps in a final step, the one-way SWD were improved to employ them for the analysis of the weather event. We found that the non-isotropic component of the one-way SWD contributes up to 11% of the SWD estimates. Moreover, we validated the SWD between ground-based water-vapour radiometry and GNSS-derived SWD for different elevation angles. Furthermore, the spatio-temporal fluctuations in the SWD as measured by GNSS closely mirrored the moisture field from the ERA5 re-analysis associated with this weather event. By employing an adequate windowing system for generating these MP correction maps in combination with high-precision real-time GNSS analysis, it is possible to provide improved SWD estimates for the tracking of severe weather events.</p>
Contact: F. N. Teferle (email: norman.teferle@uni.lu) 1) Institute of Geodesy and Geophysics, Uni... more Contact: F. N. Teferle (email: norman.teferle@uni.lu) 1) Institute of Geodesy and Geophysics, University of Luxembourg, Luxembourg 2) Centre Littoral de Geophysique, University of La Rochelle (ULR), France 3) Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany 4) British Isles continuous GNSS Facility, Nottingham Geospatial Institute, University of Nottingham, United Kingdom 5) German Geodetic Research Institute, Technical University of Munich (DGFI), Munich, Germany (6) Geoscience Australia, Canberra, Australia A. Hunegnaw (1), F.N. Teferle (1), K.E. Abraha (1), A. Santamaría-Gómez (2), M. Gravelle (2), G. Wöppelman (2), T. Schöne (3), Z. Deng (3), R.M. Bingley (4), D.N. Hansen (4), L. Sanchez (5), M. Moore (6) and M. Jia (6) Download this poster from here:
With its mid-ocean location in the Southern Atlantic Ocean South Georgia Island is in a key posit... more With its mid-ocean location in the Southern Atlantic Ocean South Georgia Island is in a key position for the oceanic and geodetic global monitoring networks. Since 2013 the tide gauge at King Edward Point (KEP) with GLOSS ID 187 has been monitored using a GNSS station nearby on Brown Mountain. By accurately geo-referencing the tide gauge and monitoring any vertical land movements, a continuous record of its datum within the Permanent Service for Mean Sea Level (PSMSL) can be established, which in turn makes the recorded and averaged sea levels useful for long-term studies and satellite altimetry calibrations. In 2014 another GNSS station was installed at KEP after local subsidence was suspected and later on, three additional GNSS stations came to service at the periphery of the main island, making it possible to monitor uplift/subsidence wider afield. Furthermore, together with four precise levelling campaigns of the KEP benchmark network in 2013, 2014 and two in 2017, it has also been possible to investigate the very local character of the vertical motions near KEP, i.e. the stability of the jetty upon which the tide gauge is mounted. In this study, we will present the results from the GNSS and precise levelling measurements, and will discuss their impact on the sea level record from the KEP tide gauge and nearby satellite altimetry sea surface heights. This study comes at a timely manner as during the Austral Summer 2019/2020 the jetty will be stabilized and enlarged, and consequently the current tide gauge will be replaced by a new one. Our measurements show that uplift is observed all over South Georgia Island while the area at the KEP jetty with tide gauge are subsiding relative to the rest of the island. In contrast, results for the tide gauge record show a lower magnitude of observed sea level rise than expected from nearby satellite altimetry. We will revisit all geodetic and oceanic observations in an attempt to improve the agreement between these measurements to summarize the status before the work at the jetty begins.
Tide Gauge Benchmark Monitoring Project: IGS Technical Report 2011
Tide Gauge Benchmark Monitoring Working Group, Technical Report
The large volume of in-and out-flow of raw materials to construction projects has a huge potentia... more The large volume of in-and out-flow of raw materials to construction projects has a huge potential to be optimised for resource efficiency and waste reduction. With the recent awareness of the importance of the circular economy, construction actors are aligning their practices to be more circular and sustainable. The concept of material banks is born out of this awareness in order to document the lifecycle information of materials and facilitate re-using them. The introduction of new cycles before individual materials reach their final lifecycle stages results in reduced negative environmental impacts. This paper presents a workflow by positioning different digital technologies to automate the procedures for reuse assessment: from the deconstructed building to M/C bank to new construction projects. This automation supports a practical material and component reuse, while it provides the necessary infrastructure to digitise and digitalise the post-deconstruction materials to be visualised, selected and used by future designers in Building Information Modelling (BIM)-based design and management environments. To this aim, the coupling of BIM, reality capturing technologies, additive manufacturing techniques, IoT and RFID sensors is also anticipated.
Calibration of the Tide Gauge at King Edward Point, South Georgia Island, South Atlantic Ocean
Norman Teferle(1), Addisu Hunegnaw(1), Kibrom Abraha(1), Philip Woodworth(2), Simon Williams(2), ... more Norman Teferle(1), Addisu Hunegnaw(1), Kibrom Abraha(1), Philip Woodworth(2), Simon Williams(2), Angela Hibbert(2), Robert Smalley(3), Ian Dalziel(4) and Larry Lawver(4)
Geodesy and Geospatial Engineering Geodesy and Geospatial Engineering Mean Sea Level (MSL) Record... more Geodesy and Geospatial Engineering Geodesy and Geospatial Engineering Mean Sea Level (MSL) Records from PSMSL • Stockholm-Glacial Isostatic Adjustment (GIA; sometimes called Post Glacial Rebound or PGR): Site near Stockholm shows large negative trend due to crustal uplift. Why monitor Vertical Land Motions at Tide Gauges ? • Tide gauges (TG) measure local sea level • Vertical land motions (VLM) are determined from CGPS and AG at or close to the tide gauge • The change in sea level de-coupled from VLM can be inferred Tide Gauge Measurement Vertical Land Motions (VLM) Change in Sea Level Decoupled From VLM 7
The standard tool within the IGS for the analysis of GNSS data quality is Teqc [Estey & Meertens,... more The standard tool within the IGS for the analysis of GNSS data quality is Teqc [Estey & Meertens, 1999]. Teqc allows the computation of a number of quality control metrics of which the most important ones include code-multipath on L1 and L2, denoted as MP1 and MP2, and the number of observations per cycle slips. The latter ratio can be expressed in terms of cycle slips per observations in 1000, leading to a number close to zero for the optimal case. Estey & Meertens [1999] describe the computation of the MP1 and MP2 metrics in detail and here we use the root-mean-square value after fitting a moving average to the absolute multipath values. The computed MP1 and MP2 metrics only partly reflect the multipath environment at a particular site as their values also dependent on the stability of receiver clocks and any receiver observation filtering. Hence, using a more stable external clock than the internal one, generally reduces the multipath metrics. Also, within the IGS the default is to disable any receiver observation filtering and we assume that none of the data used in this study have been filtered. Trimble NetR9 receivers operate at 27 stations within the global IGS tracking network (Figure 2). Furthermore, CON2 and PHIG, two sites installed and operated by Unavco Inc., use the same receiver and the same 1-metre antenna mast as KEPA. All available data from these sites have been used in this study for the period from 14 February to 10 August 2013, i.e. nearly six months.
South Georgia Island in the Southern Atlantic Ocean is a key location for the seismic, geomagneti... more South Georgia Island in the Southern Atlantic Ocean is a key location for the seismic, geomagnetic and oceanic global monitoring networks. In its sub-Antarctic location, the island is largely covered by mountain glaciers which have been reported to be retreating due to climatic change. Furthermore, during past glaciation periods the island and its shelf area have been ice covered as was revealed by scarring of the sub-oceanic topography. Together with ongoing tectonics along the North Scotia Ridge, these processes have the ability to produce significant uplift on local to regional scales, affecting the measurements of the tide gauge (GLOSS ID 187) at King Edward Point (KEP). Furthermore, with its mid-ocean location, the tide gauge is of particular interest to satellite altimetry calibrations over the Southern Atlantic and Southern Oceans. With the establishment of five GNSS stations on the islands during 2013 to 2015 and the scientific analysis of these data within the global network of stations of the International GNSS Service Tide Gauge Benchmark Monitoring (TIGA) working group, it has now become possible to study present-day vertical land movements of the region and their impacts on, for example, regional sea level. Furthermore, together with four precise levelling campaigns of the KEP benchmark network in 2013, 2014 and two in 2017, it has also been possible to investigate the very local character of the vertical motions near KEP, ie. the stability of the jetty upon which the tide gauge is mounted. In this study, we will present the still preliminary results from the GNSS and levelling measurements and will discuss their impact on the sea level record from the KEP tide gauge. Our measurements show that while South Georgia Island and the area around KEP are rising, the jetty and tide gauge are subsiding, leading to a disagreement in the observed sea level change from the tide gauge and satellite altimetry. In order to improve the agreement between these sea level measurements both local and regional vertical land movements need to be monitored.
Vertical station velocity estimates and their uncertainties: Quantifying the effects of CGPS processing strategy and reference frame implementation on coordinate time …
Sea Level Variations …
49 Vertical station velocity estimates and their uncertainties: Quantifying the effects of CGPS p... more 49 Vertical station velocity estimates and their uncertainties: Quantifying the effects of CGPS processing strategy and reference frame implementation on coordinate time series noise F. Norman Teferle1, Simon DP Williams2, Halfdan P. Kierulf3, Richard M. Bingley1, Hans-Peter ...
An assessment of precise point positioning using the Bernese GPS software version 5.0
Sea Level Variations Towards an …
57 An assessment of precise point positioning using the Bernese GPS software version 5.0 F. Norma... more 57 An assessment of precise point positioning using the Bernese GPS software version 5.0 F. Norman Teferle, Etienne J. Orliac, Richard M. Bingley Institute of Engineering Surveying and Space Geodesy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK, ...
Cross-Evaluation of Surface Meteorological Data and GNSS-derived Water Vapor with Re-analysis Information for South Georgia Island, South Atlantic Ocean
As one of the most important components of the global hydrologic cycle, atmospheric water vapor s... more As one of the most important components of the global hydrologic cycle, atmospheric water vapor shows significant variability in both space and time over a large range of scales. This variability results from the interactions of many different factors, including topography and the presence of specific atmospheric processes. One of the key regions for affecting global climatic variations lies in the sub-Antarctic zone over the Southern Ocean with its Antarctic Circumpolar Current and the associated Antarctic Convergence. There, in this cold and maritime region, lies South Georgia Island with its weather and climate being largely affected by both the dominating ocean currents and the strong east ward blowing winds in this zone. While the island forms an important outpost for various surface observations in this largely under-sampled and extremely remote region, it also forms a barrier for these winds due to its high topography, which, in turn, leads to various local meteorological phenomena, such as foehn winds. Surface meteorological data have been available for several stations near King Edward Point (KEP) on South Georgia for much of the 20th century. Since 2013 and 2014, Global Navigation Satellite System (GNSS) data have been available at five locations around the periphery of the island and during a few months in 2016 also radiosonde data have been collected at KEP. This study aims at investigating the consistency between the different surface meteorological data sets such as temperature, pressure and wind direction/speed that have been collected at KEP and a nearby GNSS station on Brown Mountain (BMT) for which we also compare the precipitable water vapor estimates. A cross-evaluation of these data sets with model values from the ERA-Interim re-analyses is carried out to further investigate the performance of both instruments and models. Overall, our preliminary results show high consistency between the surface meteorological observations and the re-analysis model values. It was our main objective to investigate the homogeneity and accuracy of the BMT observation time series through cross-evaluation with the series of the official WMO station at KEP. Air temperature and pressure at both sites from observation and model data are strongly correlated at hourly intervals, reaching correlation coefficients in the range of 0.966 - 0.968 for the former data set. The difference temperature time series shows seasonal variations but no obvious steps. The difference pressure time series is flat, also indicating no discontinuities. A cross-evaluation of the wind observations shows the distinct directional feature at KEP for a station in a valley where the winds are funneled through the valley. For BMT the wind observations confirm the main directions of winds but also show the openness of the station from all directions. The observations of temperature, pressure, humidity and GNSS-derived PWV clearly show the signatures of the frequent foehn events
Analysis of GNSS sensed slant wet delay during the severe weather events in central Europe
<p><strong>Over the last few decades, anthropogenic g... more <p><strong>Over the last few decades, anthropogenic greenhouse gas emissions have increased the frequency of climatological anomalies such as temperature, precipitation, and evapotranspiration. It is noticed that the frequency and severity of the intense precipitation signify a greater susceptibility to flash flooding. Flash flooding continues to be a major threat to European cities, with devastating mortality and considerable damage to urban infrastructure. As a result, accurate forecasting of future extreme precipitation events is critical for natural hazard mitigation. A network of ground-based GNSS receivers enables the measurement of integrated water vapour along slant pathways providing three-dimensional water vapour distributions. This study aims to demonstrate how GNSS sensing of the troposphere can be used to monitor the rapid and extreme weather events that occurred in central Europe in June 2013 and resulted in flash floods and property damage. We recovered one-way slant wet delay (SWD) by adding GNSS post-fit phase residuals, representing the troposphere's higher-order inhomogeneity. Nonetheless, noise in the GNSS phase observable caused by site-specific multipath can significantly affect the SWD from individual satellites. To overcome the problem, we employ a suitable averaging strategy for stacking post-fit phase residuals obtained from the PPP processing strategy to generate site-specific multipath corrections maps (MPS). The spatial stacking is carried out in congruent cells with an optimal resolution in elevation and azimuth at the local horizon but with decreasing azimuth resolution as the elevation angle increases. This permits an approximately equal number of observations allocated to each cell. The spatio-temporal fluctuations in the SWD as measured by GNSS closely mirrored the moisture field associated with severe weather events in central Europe, i.e., a brief rise prior to the main rain events, followed by a rapid decline once the storms passed. Furthermore, we validated the one-way SWD between ground-based water-vapour radiometry (WVR) and GNSS-derived SWD for different elevation angles.</strong></p><p> </p>
AGU Fall Meeting Abstracts, Dec 17, 2020
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Papers by Felicia N R Teferle