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Johansson, J., Lidberg, M., Jarlemark, P., Ohlsson, K., Löfgren, J., Jivall, L. & Ning, T. (2019). CLOSE-RTK 3: High-performance Real-TimeGNSS Services.
Åpne denne publikasjonen i ny fane eller vindu >>CLOSE-RTK 3: High-performance Real-TimeGNSS Services
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2019 (engelsk)Rapport (Annet vitenskapelig)
Abstract [en]

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!

Publisher
s. 172
Serie
RISE Rapport ; 2019:101
HSV kategori
Identifikatorer
urn:nbn:se:ri:diva-40747 (URN)978-91-89049-32-1 (ISBN)
Tilgjengelig fra: 2019-11-05 Laget: 2019-11-05 Sist oppdatert: 2024-05-15bibliografisk kontrollert
Lidberg, M., Jarlemark, P., Johansson, J., Ohlsson, K., Jivall, L. & Ning, T. (2019). Station calibration of the SWEPOS GNSS network. Geophysica, 54(1), 93-105
Åpne denne publikasjonen i ny fane eller vindu >>Station calibration of the SWEPOS GNSS network
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2019 (engelsk)Inngår i: Geophysica, ISSN 0367-4231, E-ISSN 2324-0741, Vol. 54, nr 1, s. 93-105Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

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.

sted, utgiver, år, opplag, sider
Finish Environment Institute, 2019
Emneord
Antenna calibration, GNSS, Local tie, Site dependent effects
HSV kategori
Identifikatorer
urn:nbn:se:ri:diva-40625 (URN)2-s2.0-85073799547 (Scopus ID)
Tilgjengelig fra: 2019-11-12 Laget: 2019-11-12 Sist oppdatert: 2024-05-15bibliografisk kontrollert
Wagner, J., Roy, A. L., Krichbaum, T. P., Alef, W., Bansod, A., Bertarini, A., . . . Inoue, M. (2015). First 230?: GHz VLBI fringes on 3C 279 using the APEX Telescope (Research Note). Astronomy and Astrophysics, 581, Article ID A32.
Åpne denne publikasjonen i ny fane eller vindu >>First 230?: GHz VLBI fringes on 3C 279 using the APEX Telescope (Research Note)
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2015 (engelsk)Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 581, artikkel-id A32Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Aims. We report about a 230? GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO). Methods. We installed VLBI equipment and measured the APEX station position to 1? cm accuracy (1σ). We then observed 3C 279 on 2012 May 7 in a 5? h 230? GHz VLBI track with baseline lengths of 2800? Mλ to 7200? Mλ and a finest fringe spacing of 28.6? μas. Results. Fringes were detected on all baselines with signal-to-noise ratios of 12 to 55 in 420? s. The correlated flux density on the longest baseline was ∼0.3? Jy beam-1, out of a total flux density of 19.8? Jy. Visibility data suggest an emission region ≤ 38? μas in size, and at least two components, possibly polarized. We find a lower limit of the brightness temperature of the inner jet region of about 1010? K. Lastly, we find an upper limit of 20% on the linear polarization fraction at a fringe spacing of ∼ 38? μas. Conclusions. With APEX the angular resolution of 230? GHz VLBI improves to 28.6? μas. This allows one to resolve the last-photon ring around the Galactic Center black hole event horizon, expected to be 40? μas in diameter, and probe radio jet launching at unprecedented resolution, down to a few gravitational radii in galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in detail, follow-up observations with APEX and five other mm-VLBI stations have been conducted (March 2013) and are being analyzed.

sted, utgiver, år, opplag, sider
EDP Sciences, 2015
Emneord
Galaxies: individual: 3C 279, Galaxies: jets, Instrumentation: high angular resolution, Telescopes, Galaxies, Radio astronomy, Radio telescopes, Signal to noise ratio, Angular resolution, Brightness temperatures, Galaxies: individuals, Galaxies:jets, Instrumentation:high angular resolution, Linear polarization, Submillimeter array, Very long baseline interferometry, Fighter aircraft
HSV kategori
Identifikatorer
urn:nbn:se:ri:diva-43926 (URN)10.1051/0004-6361/201423613 (DOI)2-s2.0-84940665971 (Scopus ID)
Tilgjengelig fra: 2020-02-14 Laget: 2020-02-14 Sist oppdatert: 2024-05-15bibliografisk kontrollert
Merlone, A., Lopardo, G., Francesca, S., Bell, S. A., Benyon, R., Bergerud, R. A., . . . Underwood, R. (2015). The MeteoMet project – metrology for meteorology: challenges and results (ed.). Meteorological Applications, 22(S1), 820-829
Åpne denne publikasjonen i ny fane eller vindu >>The MeteoMet project – metrology for meteorology: challenges and results
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2015 (engelsk)Inngår i: Meteorological Applications, ISSN 1350-4827, E-ISSN 1469-8080, Vol. 22, nr S1, s. 820-829Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The study describes significant outcomes of the ‘Metrology for Meteorology’ project, MeteoMet, which is an attempt to bridge the meteorological and metrological communities. The concept of traceability, an idea used in both fields but with a subtle difference in meaning, is at the heart of the project. For meteorology, a traceable measurement is the one that can be traced back to a particular instrument, time and location. From a metrological perspective, traceability further implies that the measurement can be traced back to a primary realization of the quantity being measured in terms of the base units of the International System of Units, the SI. These two perspectives reflect long-standing differences in culture and practice and this project – and this study – represents only the first step towards better communication between the two communities. The 3 year MeteoMet project was funded by the European Metrology Research Program (EMRP) and involved 18 European National Metrological Institutes, 3 universities and 35 collaborating stakeholders including national meteorology organizations, research institutes, universities, associations and instrument companies. The project brought a metrological perspective to several long-standing measurement problems in meteorology and climatology, varying from conventional ground-based measurements to those made in the upper atmosphere. It included development and testing of novel instrumentation as well as improved calibration procedures and facilities, instrument intercomparison under realistic conditions and best practice dissemination. Additionally, the validation of historical temperature data series with respect to measurement uncertainties and a methodology for recalculation of the values were included.

Emneord
Calibration, Earth surface observations, Historical temperature data series, Joint research project, MeteoMet, Metrology, Traceability, Upper air
HSV kategori
Identifikatorer
urn:nbn:se:ri:diva-6890 (URN)10.1002/met.1528 (DOI)2-s2.0-84954325728 (Scopus ID)30651 (Lokal ID)30651 (Arkivnummer)30651 (OAI)
Tilgjengelig fra: 2016-09-08 Laget: 2016-09-08 Sist oppdatert: 2024-05-15bibliografisk kontrollert
Emardson, R., Jarlemark, P., Johansson, J. & Sebastian, S. (2013). Spatial variability in the ionosphere measured with GNSS networks (ed.). Radio Science, 48(5), 646-652
Åpne denne publikasjonen i ny fane eller vindu >>Spatial variability in the ionosphere measured with GNSS networks
2013 (engelsk)Inngår i: Radio Science, Vol. 48, nr 5, s. 646-652Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Travelling Ionospheric Disturbances (TIDs) appear as Medium-Scale TIDs at mid-latitudes and as polar cap patches at high latitudes. Both can have a negative impact on GNSS measurements although the amplitude is of tenths of a TECU. Due to their spatial extension they affect GNSS measurements using receivers separated with distances up to ~1000 km. We present statistical measures of the ionospheric spatial variability as functions of time in solar cycle, annual season, and time of day for different geographical locations in Europe. In order to perform this spatial characterization of the ionosphere, we have used archived GPS data from a thirteen year period, 1999-2011, covering a complete solar cycle. We find that the ionospheric spatial variability is larger for the northern areas than for the southern areas. This is especially pronounced at solar maximum. For the more northern areas, the ionospheric variability is greater during night time than during day time, while for central Europe the variability is larger during day time. At solar maximum, the variability is larger during the months October and November and smaller in June and July.

Emneord
GNSS, ionosphere
HSV kategori
Identifikatorer
urn:nbn:se:ri:diva-6490 (URN)10.1002/2013RS005152 (DOI)2-s2.0-84886223924 (Scopus ID)15779 (Lokal ID)15779 (Arkivnummer)15779 (OAI)
Tilgjengelig fra: 2016-09-08 Laget: 2016-09-08 Sist oppdatert: 2024-05-15bibliografisk kontrollert
Johansson, J. & Elgered, G. (2012). The Impact of Microwave Absorber and Radome Geometries on Ground-Based GNSS Measurements of Coordinates and Atmospheric Water Vapour (ed.). Advances in Space Research., 47(2), 186-96
Åpne denne publikasjonen i ny fane eller vindu >>The Impact of Microwave Absorber and Radome Geometries on Ground-Based GNSS Measurements of Coordinates and Atmospheric Water Vapour
2012 (engelsk)Inngår i: Advances in Space Research., Vol. 47, nr 2, s. 186-96Artikkel i tidsskrift (Annet vitenskapelig) Published
HSV kategori
Identifikatorer
urn:nbn:se:ri:diva-6326 (URN)13474 (Lokal ID)13474 (Arkivnummer)13474 (OAI)
Tilgjengelig fra: 2016-09-08 Laget: 2016-09-08 Sist oppdatert: 2024-05-15bibliografisk kontrollert
Jarlemark, P., Emardson, R., Johansson, J., Bergstrand, S. & Hedling, G. (2011). Error Sources in Network RTK (ed.). In: Proceedings of the 24th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS 2011): . Paper presented at 24th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS 2011) Sept., 20-23, 2011, Oregon Convention Center, Portland, Oregon, Portland, OR.
Åpne denne publikasjonen i ny fane eller vindu >>Error Sources in Network RTK
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2011 (engelsk)Inngår i: Proceedings of the 24th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS 2011), 2011, , s. 2175-2178Konferansepaper, Publicerat paper (Fagfellevurdert)
Abstract [en]

Real Time Kinematic (RTK) is a system that utilises Global Navigation Satellite Systems (GNSS) to provide accurate positioning in real time. The contribution of the troposphere, the ionosphere and local effects, such as receiver noise and multipath are the most significant error sources affecting network RTK measurements We show how measurements with network RTK are affected by these different error sources under varying circumstances such as time of year or time of the day, network infrastructure, satellite systems and processing techniques We find that, for Scandinavian conditions, the effect of the ionospheric spatial variability on network RTK measurements is greater during nighttime than during daytime. The effect is also largest in the months October and November and smallest in the months of June and July. A densification of the reference network from 70 km to 35 km between the reference stations results in improved measurements. The error in the measured vertical position coordinate is reduced from 26 mm to 17 mm. The access to new GNSS reduces error in the measured vertical position coordinate from 26 to 21 mm. By using the L3-combination, the contribution from the ionosphere is reduced to virtually zero. However, this has been at the expense of the local errors

Publisher
s. 2175-2178
HSV kategori
Identifikatorer
urn:nbn:se:ri:diva-12346 (URN)16267 (Lokal ID)16267 (Arkivnummer)16267 (OAI)
Konferanse
24th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS 2011) Sept., 20-23, 2011, Oregon Convention Center, Portland, Oregon, Portland, OR
Tilgjengelig fra: 2016-09-13 Laget: 2016-09-13 Sist oppdatert: 2024-05-15bibliografisk kontrollert
Emardson, R., Jarlemark, P., Bergstrand, S. & Johansson, J. (2011). Ionospheric Effects on Network-RTK (ed.).
Åpne denne publikasjonen i ny fane eller vindu >>Ionospheric Effects on Network-RTK
2011 (engelsk)Rapport (Fagfellevurdert)
Abstract [en]

A part of the atmosphere is ionized by the UV radiation from the Sun. This part is often referred to as the ionosphere. The resulting free electrons influence the GNSS signals as they propagate through the ionosphere. We have studied how the spatial variations of electron density in the ionosphere affect measurements with network-RTK. The aim is to predict what we can expect from measurements during the next solar maximum that is expected to occur around 2012. In order to perform a spatial characterization of the ionosphere, we have used archived GPS data from SWEPOS from a five year period, 1999-2004, around the previous solar maximum. We find that the effect of the ionospheric spatial variability on network-RTK measurements is greater during night time than during day time. It is also clear that the effect is larger for northern Sweden than for the southern part. This is especially true during night time. The effect is also largest in the months October and November and smallest in June and July. Also the number of cycle slips is larger in northern Sweden than in southern Sweden. We find that when monitoring the ionosphere and its influence on network-RTK performance it is desirable to have several different geographical regions under observation. The effects in northern Sweden may, for example not be that relevant for a user in southern Sweden. In this report we define the ionospheric delay errors as the standard deviation of the difference between the ionospheric delay at L1 at one location and the estimated value of this based on the three surrounding reference stations with 70 km separation. Using GNSS equipment that is state-of-the art around 2010, we find that when conditions are such that the ionospheric delay error is below 10 mm, which occurs some 70% of the time, a rover is able to fix the ambiguities more than 90% of the time. This ability decreases with increasing ionospheric variability and when the ionospheric delay error is larger than 25 mm, which occurs some 10% of the time, the rover ability to fix is less than 50%. When measuring with network-RTK during the next solar maximum, approximately, 80% of the time, we have conditions such that a rover has at least 75% chance of fixing the solutions. Overall the probability to find a correct fix solution when performing RTK measurements during the next solar maximum is approximately 85% and the mean time to fix is 55 seconds.

Serie
SP Rapport, ISSN 0284-5172 ; 2011:80
HSV kategori
Identifikatorer
urn:nbn:se:ri:diva-4982 (URN)12637 (Lokal ID)978-91-87017-13-1 (ISBN)12637 (Arkivnummer)12637 (OAI)
Tilgjengelig fra: 2016-09-07 Laget: 2016-09-07 Sist oppdatert: 2024-05-15bibliografisk kontrollert
Johansson, J., Löfgren, J. & Haas, R. (2011). Monitoring coastal sea level using reflected GNSS signals (ed.). Journal of Advances in Space Research, Scientific applications of Galileo and other Global Navigation Satellite Systems., 47(2), 213-20
Åpne denne publikasjonen i ny fane eller vindu >>Monitoring coastal sea level using reflected GNSS signals
2011 (engelsk)Inngår i: Journal of Advances in Space Research, Scientific applications of Galileo and other Global Navigation Satellite Systems., Vol. 47, nr 2, s. 213-20Artikkel i tidsskrift (Annet vitenskapelig) Published
HSV kategori
Identifikatorer
urn:nbn:se:ri:diva-6257 (URN)13470 (Lokal ID)13470 (Arkivnummer)13470 (OAI)
Tilgjengelig fra: 2016-09-08 Laget: 2016-09-08 Sist oppdatert: 2024-05-15bibliografisk kontrollert
Scherneck, H.-G., Lidberg, M., Haas, R., Johansson, J. & Milne, G. A. (2010). Fennoscandian strain rates from BOFROST GPS: A gravitating, thick-plate apporach (ed.). Journal of Geodynamics, 50, 19-26
Åpne denne publikasjonen i ny fane eller vindu >>Fennoscandian strain rates from BOFROST GPS: A gravitating, thick-plate apporach
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2010 (engelsk)Inngår i: Journal of Geodynamics, ISSN 0264-3707, E-ISSN 1879-1670, Vol. 50, s. 19-26Artikkel i tidsskrift (Fagfellevurdert) Published
HSV kategori
Identifikatorer
urn:nbn:se:ri:diva-6189 (URN)12038 (Lokal ID)12038 (Arkivnummer)12038 (OAI)
Tilgjengelig fra: 2016-09-08 Laget: 2016-09-08 Sist oppdatert: 2024-05-15bibliografisk kontrollert
Organisasjoner
Identifikatorer
ORCID-id: ORCID iD iconorcid.org/0000-0001-9736-8546
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