| 1. |
- Jivall, Lotti, et al.
(författare)
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Analysis of 20 years of GPS data from SWEREF consolidation points – using BERNESE and GAMIT-GLOBK software
- 2022
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Rapport (populärvet., debatt m.m.)abstract
- The SWEREF 99 national geodetic reference frame has been used in Sweden since 2007 and it was adopted by EUREF in 2000 as the national realisation of ETRS89 in Sweden [Jivall and Lidberg, 2000]. The SWEREF 99 reference frame is defined by an active approach through the 21 original (fundamental) SWEPOS GNSS stations, hence relying on positioning services such as the network real time kinematic (NRTK) and post processing services. The SWEREF 99 coordinates are assumed to be fixed in time and no temporal variations are expected. However, the stability of the stations and their coordinates can be altered due to equipment change or software as well as local movements at the reference stations.To be able to check all alterations mentioned above and having a backup national network of GNSS points, approximately 300 passive so-called consolidation points are used. The consolidation points are a subset (the main part) of the so-called SWEREF points established from 1996 and onwards. All 300 points are remeasured with static GNSS for 2x24 hours using choke ring antennas on a yearly basis with 50 points each year. The original data processing was done with the Bernese GNSS software in a regular basis and the reprocessing was carried out with both the Bernese and the GAMIT-GLOBK software packages during 2017-2018.The resulting coordinates in SWEREF 99 from GAMIT and Bernese processing are equal at 1–2 mm level for the horizontal and 4 mm for the vertical components (1 sigma) when using almost the same models and processing strategy. The result from the original processing, which partly is based on other models and parameters, differs slightly more for the north component compared to the reprocessing results (RMS of 2 mm compared to 1 mm).Our analysis both of Bernese and GAMIT results shows that the standard uncertainties for a single SWEREF 99 coordinate determination (with 2x24 hrs observation) is about 2 mm for the horizontal components and 6 mm in height. It is interesting to note that the coordinate repeatability is on the same level also for the original processing, where we have differences in models and parameters used during the years. This indicates that our concept for determining SWEREF 99 coordinates has worked well on the mentioned uncertainty level.We performed trend analysis and statistical tests for the points having minimum three observations to investigate the stability of the estimated SWEREF 99 coordinates. The low rate of redundancy (just one redundant observation in case of three observations) was a problem so a modified version of the F-test was developed which gave good agreement with visual interpretation of the time series. This strategy showed that about 10% of the points had trends (with notable movements), but we should be aware of the low redundancy. With more observations in the future, we can determine trends more reliably.We will continue to analyse the point coordinate repeatability and trends when we get more data. Further on, some reprocessing is needed to be compatible with the SWEREF 99 update 2021 at SWEPOS. We will also study the effect of using different satellite systems and finally prepare for the publication of updated coordinates in the Digital Geodetic Archive (DGA) provided by Lantmäteriet.
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| 2. |
- Jivall, Lotti, et al.
(författare)
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Mast-based versus Pillar-based Networks for Coordinate Estimation of SWEREF points : – using the Bernese and GAMIT-GLOBK Software Packages
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- For about 20 years, the fundamental pillar stations in SWEPOS network (the Swedish Permanent GNSS network) have been used as the carrier of the Swedish national reference frame, SWEREF 99, and used as control points for several geodetic and geodynamic studies. Today, each pillar station has a close-by truss mast station, mostly in 10 meters distance. Switching from pillar-based network to mast-based network (with stations equipped with more modern receivers and calibrated antennas), as reference network,need careful analysis, for example, comparing solutions from these networks. In this study, we use both the Bernese GNSS Software (BSW) and GAMIT-GLOBK softwareand process the same data set with almost the same processing strategy and compare the results. Our solutions and their comparisons show that BSWhas slightly lower rate of resolved integer ambiguities for the mast-basednetwork compared to the pillar-basednetwork (3-4percentage pointsfor the selected 14 SWEREF points and 1-2percentage pointsfor all SWEREFpoints (50) processed in this study).For GAMIT-GLOBK, we don’tsee any significant difference in the rate of resolved integer ambiguities between the network types.Furthermore, the comparison of resulting coordinates between the two software, show avery good compliancefor the pillar-based network (on average at the 1 mm level for the horizontal components and 2 mm for the height component), but for the mast-based network there is 3-4 mm systematic difference in the height component.The good compliance between the GAMIT-GLOBK and BSW solutions for the pillar network,makes it possible to use results also from GAMIT-GLOBK for coordinate determination of SWEREF points. The systematic height difference between the two software solutions for the mast-based network,as well as slightly degraded quality measures mainlyfor BSW,indicate that there are some problems with the mast stations that need further investigation.
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| 3. |
- Johansson, Jan, et al.
(författare)
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CLOSE-RTK 3: High-performance Real-TimeGNSS Services
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report presents the results from the third project of the CLOSE effort (Chalmers,Lantmäteriet, Onsala, RISE). The first project, CLOSE-RTK, investigated error sources inNetwork-RTK and simulated how to improve the performance. The results were used as a basisfor the densification, improvement and development of SWEPOS(https://swepos.lantmateriet.se/ ) during the last decade. The second project investigated how theionosphere effects the Network-RTK services.When the SWEPOS network are densified, the measurement uncertainty in the services arereduced. Thus, there is a need to continuously work in order to minimize effects from allsignificant error sources. Based on indications and experience from some 25 years operation ofSWEPOS, we have here focused on effects and error sources related to GNSS referencestations. Several new GNSS monuments are installed in the vicinity of the new Twin telescopesat the Onsala Space Observatory. Four good locations for permanent GNSS installations wereequipped with steel-grid masts serving as monuments for permanent GNSS installations. In twoof these, the installation has been untouched over a period extending over one year, while twohave been used to experiment with different installations of antennas, radomes, masthead, andthe environment of the receiving systems. The purpose of CLOSE-RTK III has been both toimprove the knowledge of the station-dependent effects in SWEPOS, and to quantify sucheffects by analyzing the collected observational data. Thus, the first work package has had theultimate goal to provide knowledge and recommendations when building a new GNSS stationand choosing the equipment to be used. The first work package also addresses the issue of somespecific station-dependent effects such as the monument stability as a function of airtemperature and sun radiation. The most important and significant results from these testsrelates to the effects of using different radomes and antennas. The influence of adding a tribrachbetween the antenna and the mast as well as adding a microwave-absorbing plate at the stationshas been investigated in detail. Furthermore, this study has looked in to the problem with birdslanding on the antennas in order to keep watch over the surrounding. A bird-detection algorithmhas been developed within the project.In second work package we investigate the necessity, and possibility, to develop methods forstation-dependent calibration in addition to the antenna-specific calibrations used to today.Since the performance of positioning services, e.g. Network-RTK, is steadily improved the errorsources related to the continuously operating reference stations may soon be limiting factors forfurther improvement of performance. Station dependent effects are thus important in highaccuracy GNSS positioning. Electrical coupling between the antenna and its near-fieldenvironment changes the characteristics of the antenna from what has been determined in e.g.absolute robot or chamber calibration.When using the presently available antenna models GNSS determination of the heightdifference between the SWEPOS pillar antennas and the surrounding reference antennas gave ~10 mm too low heights for the SWEPOS antennas. This error was derived from a comparisonwith conventional terrestrial surveys. The result varied significantly between days, and alsobetween different processing strategies. PCO/PCV errors derived from GNSS phase differencesshowed clear elevation-angle signatures that may cause systematic differences in the estimatedheight component and atmospheric delay, respectively. Electromagnetic coupling between theantenna and a metal plate below the antennas is probably contributing to the systematicPCO/PCV errors found.Starting already in 2008 and continued in this project we have developed methods andcarried out in-situ station calibration of the core permanent reference stations in SWEPOS. The station calibration intends to determine the electrical center of the GNSSantenna, as well as the PCV (phase center variations) when the antenna is installed at aSWEPOS station. The purpose of the calibration has been to examine the site-dependenteffects on the height determination as well as to establish site-dependent PCVs as acomplement to absolute calibrations of the antenna-radome pair.Our results have implications on a number of practical applications. To be mentioned isdetermination of the “local tie” between the GNSS reference point and the one from otherinstrumentation at fundamental geodetic stations. Usually, the L1 observable are used whileobserving the local GNSS networks in order to get as precise results as possible. But when usedin the IGS, the L3 (ionosphere-free) observable is used and also solving for troposphere delays.Thus, an error at the 1 cm level is easily introduced due to PCO/PCV errors.Since there are also other concepts emerging for precise real-time positioning, besides the so farused VRS-concept, the potential of these new concepts (MAC and PPP) are investigated inwork package three. Basically, the requirements from the infrastructure are invariant of thechosen concept if we aim for a certain level of performance. There is e.g. an ongoingdevelopment of real time methods for Precise Point Positioning (PPP) based on local or regionalaugmentation systems often referred to as PPP-RTK. The present development also includednew satellite signals and systems, thus, make available a three-frequency technique. The reportalso provides a schematic plan how such a service, based on PPP-RTK or rather Network-RTK,could be provided in the region of the Baltic Sea.Finally, the design of a high precision positioning service for the Baltic Sea are investigated.Motivation is that international vessel-traffic could be further optimized if the uncertainty ofvertical component in the navigation could be improved. The performance in the “Baltic Seanavigation service” would benefit from installation of some few off-shore GNSS referencestations that would be possible to locate to relatively shallow waters!
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| 4. |
- Lidberg, Martin, 1964, et al.
(författare)
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Station calibration of the SWEPOS GNSS network
- 2019
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Ingår i: Geophysica. - : Finish Environment Institute. - 0367-4231 .- 2324-0741. ; 54:1, s. 93-105
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Tidskriftsartikel (refereegranskat)abstract
- The performance of GNSS based positioning services is improving to the benefit of the users, and the uncertainties from densified RTK networks for construction work is approaching the sub-centimeter level also in the vertical. The error sources related to the continuously operating reference stations (CORS) may therefore soon be limiting factors for further improvement of performance. Station dependent effects are thus important in high accuracy GNSS positioning. Electrical coupling between the antenna and its near-field environment changes the characteristics of the antenna from what has been determined in e.g. absolute robot or chamber calibrations. Since the first initial tests back in 2008, Lantmäteriet together with Chalmers University of Technology and Research Institute of Sweden (RISE), has carried out in-situ station calibration of its network of permanent reference stations, SWEPOS. The station calibration intends to determine the electrical center of the GNSS antenna, as well as the PCV (phase center variations) when the antenna is installed at a SWEPOS station. One purpose of the calibration is to examine the site-dependent effects on the height determination in SWEREF 99 (the national reference frame). Another purpose is to establish PCV as a complement to absolute calibrations of the antenna-radome pair. In this paper we present both the methodology for observation procedure in the field and the method for the analysis, together with results of the station-dependent effects on heights as well as PCV from the analysis. Some strength and weakness of our method for GNSS station calibration are discussed at the end.
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| 5. |
- Mårtensson, Stig-Göran, et al.
(författare)
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Measurement uncertainty in network RTK GNSS-based positioning of a terrestrial laser scanner
- 2012
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Ingår i: Journal of Applied Geodesy. - Tyskland : Walter de Gruyter. - 1862-9024 .- 1862-9016. ; 6:1, s. 25-32
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on investigation of measurement uncertainty in positioning of a terrestrial laser scanner with network RTK (Real-Time Kinematic) service provided by SWEPOS®, Swedish national network of permanent reference stations for GNSS (Global Navigation Satellite System). To simulate measurements by a scanner, a rotating flat bar fixed to a prism base, attached to a tribrach, was used. The tests have been carried out with both a rotating GNSS antenna (placed at different distances from the centre of rotation – radii) and a stationary antenna, under different time intervals (1–5 min). The results show that it is possible to achieve a standard uncertainty of less than 10 mm in plane and 16 mm in height, independently of the observation time and radius. Hence, network RTK can be used with advantage for precise direct georeferencing of point clouds, not only for determination of the position of the scanner, but also its orientation.
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| 6. |
- Nilfouroushan, Faramarz, 1968-, et al.
(författare)
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Evaluation of newly installed SWEPOS mast stations, individual vs. type PCV antenna models and comparison with pillar stations
- 2016
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Ingår i: Geophysical Research Abstracts. - Vienna : European Geosciences Union.
-
Konferensbidrag (refereegranskat)abstract
- For about two decades, SWEPOS (the Swedish Permanent GNSS network) pillar stations have been used indifferent geodetic and geodynamic studies. To keep continuous measurements of these long lived pillar stationsand at the same time modernizing the SWEPOS network, it has been decided to install new truss mast stations,equipped with modern and individually calibrated antennas and radomes, capable of tracking all new GNSSsatellites. Installation of mast stations started in 2011. Today, each pillar station in the SWEPOS permanent GNSSnetwork has a close-by truss mast station, mostly in 10 meters distance with individual calibrated Leica chokering antenna and its attachment (LEIAR25.R3, LEIT). Due to their closeness to pillars, the modern mast stationsmay provide additional information for the analysis of ground movements in Sweden e.g. to distinguish betweentectonic and geodynamic processes (e.g. land uplift in Sweden).In this study, we have used two datasets from two different seasons for 21 pillars and 21 mast stations andformed different networks. The mast network has been processed using both IGS standard (type) and individuallycalibrated PCV (Phase Center Variation) models and therefore the effect of these two different PCV models onheight components has been investigated. In a combined network, we processed all 42 stations (21 pillars+21mast) to see how this multi-baseline network (861 baselines) combination differs from independent mast or pillarnetworks with much less baselines (210 baselines). For our analysis, we used the GAMIT-GLOBK softwareand compared different networks. Ambiguity resolutions, daily coordinate repeatability and differences betweenheight components in different solutions are presented. Moreover, the GAMIT and BERNESE solutions forcombined mast and pillar networks are compared.Our results suggest that the SWEPOS truss mast stations can reliably be used for crustal deformation studies.The comparison between pillar and mast stations shows similar time series for different horizontal and verticalcomponents and their Normalized rms (nrms) and weighted rms (wmrs) are almost equal.Comparison of standard and calibrated PCV models for mast stations show notable differences in height compo-nents and reach up to14 mm. These differences are antenna-dependent and are not systematic offsets. Therefore,whenever available, individual calibrated antenna models have to be used instead of standard (type) calibratedmodels.This study is part of the Swedish CLOSE III research project between Lantmäteriet, SP, and Chalmers Universityof Technology.
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| 7. |
- Nilfouroushan, Faramarz, Senior Lecturer, 1968-, et al.
(författare)
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Maintenance of the National Realisation of ETRS89 in Sweden: re-analysis of 20-years GPS data for SWEREF stations
- 2019
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Ingår i: EUREF 2019 Symposium.
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Konferensbidrag (refereegranskat)abstract
- The national geodetic reference frame of Sweden called SWEREF 99, was adopted in 2000 by EUREF as therealization of ETRS89 in Sweden and was officially introduced in 2001 as a national reference frame, thateventually in 2007 replaced the former reference frame. The SWEREF 99 reference frame is defined by an activeapproach through the 21 fundamental SWEPOS permanent GNSS stations, hence relying on positioning servicessuch as the network real time kinematic (NRTK) and post processing service. The SWEREF 99 coordinates areassumed to be fixed in time and no temporal variations are expected. However, the stability of the stations andtheir coordinates can be altered due to equipment change or software as well as local movements at the referencestations.To be able to check all alterations mentioned above and having a backup national network of GNSS stations,approximately 300 passive so-called consolidation stations are used. The consolidation stations are a subset (mainpart) of the so-called SWEREF stations established from 1996 and onwards. All 300 stations are remeasured withstatic GNSS for 2x24 hours using choke ring antennas on a yearly basis with 50 stations each year. The originalprocessing was done with the Bernese GNSS software (here called Bernese original) and the reprocessing wascarried out with both the Bernese and the GAMIT-GLOBK software packages during 2017-2018.The resulting coordinates in SWEREF 99 from GAMIT and Bernese processing are equal at 1.2 mm level forhorizontal and 4 mm for vertical components (1 sigma) when using the same models and processing strategy.The original processing, which partly is based on other models and parameters, differs slightly more (rms 2.4mm) for the north component. Our analysis both from Bernese and GAMIT shows that the standard uncertaintiesfor a single SWEREF 99 determination (2x24 hrs) is 2 mm for the horizontal components and 6-7 mm inheight. However, since some stations are slowly moving they have slightly increased the estimated uncertainties.It is interesting to note that the repeatability is on the same level also for the original processing, where wehave differences in models and parameters used during the years. This indicates that the SWEREF-concept ofdetermining SWEREF99 coordinates has worked well on the mentioned uncertainty level.We performed trend analysis and statistical tests to investigate the stability of the estimated SWEREF 99coordinates. The analysed station time series (minimum three observations) showed that about 14% of the stationshad significant trends at the 95%-level. The possible explanation for those trends can be either local deformationand/or residuals of uplift model and/or computational effects such as lack of good or enough close-by stations forHelmert transformations from ITRF to SWEREF 99.The outcomes of the new processing and analysis reported here, are used to analyse the stability of SWEREF99 after two decades. The results have also been used to define the SWEREF 99 component in the fit of theSWEN17_RH2000 new geoid model to SWEREF 99 and RH 2000 (Swedish realization of EVRS).
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| 8. |
- Nilfouroushan, Faramarz, Senior Lecturer, 1968-, et al.
(författare)
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Reprocessing and analysis of 20-years SWEREF stations GPS data using BERNESE and GAMIT software
- 2018
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Konferensbidrag (refereegranskat)abstract
- SWEREF 99 has been used as the national geodetic reference frame in Sweden since 2007 and is adopted by EUREF as an ETRS89 realization. It is defined by an active approach through the 21 original SWEPOS stations, hence relying on positioning services like the network RTK service and the post processing service. All alterations of equipment and software as well as movements at the reference stations will in the end affect the coordinates. For checking the effect of all alterations mentioned above and having a backup network of GNSS stations, approximately 300 nationally distributed passive so-called consolidation points are used. The main part of the consolidation points consists of so-called SWEREF points established already with the beginning in the mid-1990s. All stations are remeasured with static GNSS for 2x24 hours using choke ring antennas in a 6 years base with 50 points each year. The original processing was done with the Bernese GNSS software and the reprocessing was carried out with both the Bernese GNSS software and the GAMIT software in 2017-18 covering so far 20 years of data. The station coordinates were first estimated in ITRF2008 and then transformed to SWEREF 99 using the new land uplift model NKG2016LU and close by reference stations. The outcome will be used to analyse the stability of SWEREF 99 after two decades and has been used to define the SWEREF 99 component in the fit of the SWEN17_RH2000 geoid model to SWEREF 99 and RH 2000. Our analysis show a very good agreement between repeated measurements. The mean RMS of the SWEREF 99 coordinates which have had 3-times measurements (every ~6 years) is 2 mm for the horizontal components and 5-6 mm for height. Moreover, we did trend analysis to investigate the stability of the stations and check if any systematic trend exists in the transformed SWEREF99 coordinates. In general, no significant trend was observed. However, at some stations trends were observed due to local ground movements.
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