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Publications (10 of 19) Show all publications
Bergstrand, S., Herbertsson, M., Rieck, C., Spetz, J., Svantesson, C.-G. & Haas, R. (2019). A gravitational telescope deformation model for geodetic VLBI. Journal of Geodesy, 93(5), 669-680
Open this publication in new window or tab >>A gravitational telescope deformation model for geodetic VLBI
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2019 (English)In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, Vol. 93, no 5, p. 669-680Article in journal (Refereed) Published
Abstract [en]

We have measured the geometric deformations of the Onsala 20 m VLBI telescope utilizing a combination of laser scanner, laser tracker, and electronic distance meters. The data put geometric constraints on the electromagnetic raypath variations inside the telescope. The results show that the propagated distance of the electromagnetic signal inside the telescope differs from the telescope’s focal length variation, and that the deformations alias as a vertical or tropospheric component. We find that for geodetic purposes, structural deformations of the telescope are more important than optic properties, and that for geodetic modelling the variations in raypath centroid rather than focal length should be used. All variations that have been identified as significant in previous studies can be quantified. We derived coefficients to model the gravitational deformation effect on the path length and provide uncertainty intervals for this model. The path length variation due to gravitational deformation of the Onsala 20 m telescope is in the range of 7–11 mm, comparing elevation 0$$^{\circ }$$∘and 90$$^{\circ }$$∘, and can be modelled with an uncertainty of 0.3 mm.

National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-36562 (URN)10.1007/s00190-018-1188-1 (DOI)2-s2.0-85053236319 (Scopus ID)
Available from: 2018-12-06 Created: 2018-12-06 Last updated: 2019-06-28Bibliographically approved
Svensson, S., Rieck, C., Bideberg, G. & Larsson, B. (2018). A PMU Calibration System. In: CPEM 2018 - Conference on Precision Electromagnetic Measurements: . Paper presented at 2018 Conference on Precision Electromagnetic Measurements, CPEM 2018, 8 July 2018 through 13 July 2018.
Open this publication in new window or tab >>A PMU Calibration System
2018 (English)In: CPEM 2018 - Conference on Precision Electromagnetic Measurements, 2018Conference paper, Published paper (Refereed)
Abstract [en]

There is a need for traceable calibrations of Phasor measurement units, which measures the phase angle of power system signals with respect to the universal time. This paper describes the design of such a calibration system. The system utilizes a fast A-D converter, synchronized to the Swedish time and frequency realization. The speed and synchronization makes the calibration and adjustment fast and relatively straight-forward. Coaxial dividers and shunts are used for system control. The goal is a three-phase system with an angular uncertainty in the order of, or better than ±0.002° or ±100 ns.

Keywords
calibration, Measurement, phase angle, phasor measurement standards, traceability, UTC, Phase measurement, Angular uncertainty, Measurement standards, Phase angles, Power system signal, Three phase system, Time and frequencies, Traceable calibration, Phasor measurement units
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-36602 (URN)10.1109/CPEM.2018.8501235 (DOI)2-s2.0-85057058820 (Scopus ID)9781538609736 (ISBN)
Conference
2018 Conference on Precision Electromagnetic Measurements, CPEM 2018, 8 July 2018 through 13 July 2018
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2018-12-17Bibliographically approved
Jaldehag, K., Rieck, C. & Jarlemark, P. (2018). Evaluation of CGGTTS time transfer software using multiple GNSS constellations. In: : . Paper presented at 2018 European Frequency and Time Forum (EFTF) (pp. 159-166).
Open this publication in new window or tab >>Evaluation of CGGTTS time transfer software using multiple GNSS constellations
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A new software tool for GNSS time transfer implementing the Common GNSS Generic Time Transfer Standard (CGGTTS) has been developed by the time and frequency group at RISE Research Institutes of Sweden. The software handles signals from the satellite navigation systems GPS, GLONASS, Galileo and BeiDou including the most important ranging codes for time transfer applications. The aim of the development is to provide an alternative to existing software and to support time transfer with new GNSS. The paper presents an evaluation of CGGTTS data calculated with the new software tool in comparison with those calculated using two other, independently developed software tools. It is shown that the results obtained from the different software agree to the sub-nanosecond level. Specifically, the agreement seen between individual GPS, Galileo and BeiDou CGGTTS data is at the 100- to 200-picosecond level. Similarly, GLONASS CGGTTS data agree to the sub-nanosecond level. Further, the paper presents a comparison between time transfer links for both long baselines and short, common-clock baselines obtained from a common view analysis of CGGTTS data from the four mentioned GNSS, as well as a combination of them. It finally discusses other features available from the RISE software, such as non-smoothed CGGTTS data, adoption of satellite orbit and clock products from the IGS as well as the results of an evaluation using linear combinations with non-standard CGGTTS codes and signals.

Keywords
Global navigation satellite system, Global Positioning System, Receivers, Satellites, Software tools, Standards, GNSS, Time Transfer, CGGTTS, Software, IGS
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-34325 (URN)10.1109/EFTF.2018.8409022 (DOI)2-s2.0-85050763645 (Scopus ID)
Conference
2018 European Frequency and Time Forum (EFTF)
Available from: 2018-08-07 Created: 2018-08-07 Last updated: 2019-01-08Bibliographically approved
Rieck, C., Jarlemark, P. & Jaldehag, K. (2018). Passive utilization of the TWSTFT technique. In: : . Paper presented at 2018 European Frequency and Time Forum (EFTF) (pp. 263-269).
Open this publication in new window or tab >>Passive utilization of the TWSTFT technique
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

As an active technique TWSTFT is limited in the number of concurrent users on the same communication channel. Using the transmissions of the reference network, passive users can observe the signals in a common view sense and by knowing the orbit of the relaying satellite, corrections describing the dynamic path delay can be used to estimate the clock difference between passive stations. Reliable orbit determination can be achieved using all the active measurements performed by the regular active users. For the EU/US network using Telesat Telstar 11N, the orbit estimation uncertainty is in the order of 1m for the area spanned by the contributing stations. The corresponding time uncertainty for a passive user is about 1 ns, slightly larger than achievable by active links. A passive use of TWSTFT may provide increased timing resiliency for a number of applications. The design of a passive ground station based on a SDR receiver is suggested.

Keywords
Orbits, Extraterrestrial measurements, Delays, Satellites, Real-time systems, Atmospheric measurements, Current measurement, TWSTFT, time transfer, orbit determination, passive approach, real-time, resiliency
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-34326 (URN)10.1109/EFTF.2018.8409046 (DOI)2-s2.0-85050723601 (Scopus ID)
Conference
2018 European Frequency and Time Forum (EFTF)
Available from: 2018-08-07 Created: 2018-08-07 Last updated: 2019-01-10Bibliographically approved
Jiang, Z., Zhang, V. S., Huang, Y. J., Achkar, J., Piester, D., Lin, S. Y., . . . Whibberley, P. B. (2018). Use of software-defined radio receivers in two-way satellite time and frequency transfers for UTC computation. Metrologia, 55(5), 685-698
Open this publication in new window or tab >>Use of software-defined radio receivers in two-way satellite time and frequency transfers for UTC computation
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2018 (English)In: Metrologia, ISSN 0026-1394, E-ISSN 1681-7575, Vol. 55, no 5, p. 685-698Article in journal (Refereed) Published
Abstract [en]

Two-way satellite time and frequency transfer (TWSTFT) is a primary technique for the generation of coordinated universal time (UTC). About 20 timing laboratories around the world continuously operate TWSTFT using satellite time and ranging equipment (SATRE19) modems for remote time and frequency comparisons in this context. The precision of the SATRE TWSTFT as observed today is limited by an apparent daily variation pattern (diurnal) in the TWSTFT results. The observed peak-to-peak variation have been found as high as 2 ns in some cases. Investigations into the origins of the diurnals have so far provided no complete understanding about the cause of the diurnals. One major contributor to the diurnals, however, could be related to properties of the receive part in the modem. In 2014 and 2015, it was demonstrated that bypassing the receive part and the use of software-defined radio (SDR) receivers in TWSTFT ground stations (SDR TWSTFT) instead could considerably reduce both the diurnals and the measurement noise. In 2016, the International Bureau of Weights and Measures (BIPM) and the Consultative Committee for Time and Frequency (CCTF) working group (WG) on TWSTFT launched a pilot study on the application of SDR receivers in the TWSTFT network for UTC computation. The first results of the pilot study were reported to the CCTF WG on TWSTFT annual meeting in May 2017, demonstrating that SDR TWSTFT shows superior performance compared to that of SATRE TWSTFT for practically all links between participating stations. In particular, for continental TWSTFT links, in which the strongest diurnals appear, the use of SDR TWSTFT results in a significant suppression of the diurnals by a factor of between two and three. For the very long inter-continental links, e.g. the Europe-to-USA links where the diurnals are less pronounced, SDR TWSTFT achieved a smaller but still significant gain of 30%. These findings are supported by an evaluation of some of the links with an alternate technique based on GPS signals (GPS IPPP) as reported in this paper. Stimulated by these results, the WG on TWSTFT prepared a recommendation for the 21st CCTF meeting, which proposed the introduction of SDR TWSTFT in UTC generation. With CCTF approval of the recommendation, a roadmap was developed for the implementation of SDR TWSTFT in UTC generation. In accordance with the roadmap, most of the stations that participated in the pilot study have updated the SDR TWSTFT settings to facilitate the use of SDR TWSTFT data in UTC generation. In addition, the BIPM conducted a final evaluation to validate the long-term stability of SDR TWSTFT links, made test runs using the BIPM standard software for the calculation of UTC, now including SDR TWSTFT data, and started to calculate SDR TWSTFT time links as backup from October 2017. The use of SDR TWSTFT in UTC generation will begin in 2018.

Keywords
diurnal, SDR, time transfer, TWSTFT, uncertainty, UTC, Analog circuits, Global positioning system, Modems, Radio, Radio receivers, Satellites, Software testing, Time measurement, Units of measurement, Coordinated universal time, Software Defined Radio (SDR), Time- and frequency comparisons, Two-way satellite time and frequency transfers, Software radio
National Category
Physical Sciences
Identifiers
urn:nbn:se:ri:diva-37288 (URN)10.1088/1681-7575/aacbe6 (DOI)2-s2.0-85053907924 (Scopus ID)
Available from: 2019-01-18 Created: 2019-01-18 Last updated: 2019-03-28Bibliographically approved
Jiang, Z., Zhang, V., Huang, Y.-J., Achkar, J., Piester, D., Lin, S.-Y., . . . Whibberley, P. (2018). Use of software-defined radio receiversin two-way satellite time and frequencytransfers for UTC computation. Metrologia, 55, 685-698
Open this publication in new window or tab >>Use of software-defined radio receiversin two-way satellite time and frequencytransfers for UTC computation
Show others...
2018 (English)In: Metrologia, ISSN 0026-1394, E-ISSN 1681-7575, Vol. 55, p. 685-698Article in journal (Refereed) Published
Abstract [en]

Two-way satellite time and frequency transfer (TWSTFT) is a primary technique for thegeneration of coordinated universal time (UTC). About 20 timing laboratories around theworld continuously operate TWSTFT using satellite time and ranging equipment (SATRE19)modems for remote time and frequency comparisons in this context. The precision of theSATRE TWSTFT as observed today is limited by an apparent daily variation pattern (diurnal)in the TWSTFT results. The observed peak-to-peak variation have been found as high as 2 nsin some cases. Investigations into the origins of the diurnals have so far provided no completeunderstanding about the cause of the diurnals. One major contributor to the diurnals, however,could be related to properties of the receive part in the modem. In 2014 and 2015, it wasdemonstrated that bypassing the receive part and the use of software-defined radio (SDR) receivers in TWSTFT ground stations (SDR TWSTFT) instead could considerably reduce boththe diurnals and the measurement noise.In 2016, the International Bureau of Weights and Measures (BIPM) and the ConsultativeCommittee for Time and Frequency (CCTF) working group (WG) on TWSTFT launched a pilotstudy on the application of SDR receivers in the TWSTFT network for UTC computation.The first results of the pilot study were reported to the CCTF WG on TWSTFT annualmeeting in May 2017, demonstrating that SDR TWSTFT shows superior performancecompared to that of SATRE TWSTFT for practically all links between participating stations.In particular, for continental TWSTFT links, in which the strongest diurnals appear, the useof SDR TWSTFT results in a significant suppression of the diurnals by a factor of betweentwo and three. For the very long inter-continental links, e.g. the Europe-to-USA links wherethe diurnals are less pronounced, SDR TWSTFT achieved a smaller but still significant gainof 30%. These findings are supported by an evaluation of some of the links with an alternatetechnique based on GPS signals (GPS IPPP) as reported in this paper.Stimulated by these results, the WG on TWSTFT prepared a recommendation for the 21stCCTF meeting, which proposed the introduction of SDR TWSTFT in UTC generation. WithCCTF approval of the recommendation, a roadmap was developed for the implementationof SDR TWSTFT in UTC generation. In accordance with the roadmap, most of the stationsthat participated in the pilot study have updated the SDR TWSTFT settings to facilitatethe use of SDR TWSTFT data in UTC generation. In addition, the BIPM conducted a finalevaluation to validate the long-term stability of SDR TWSTFT links, made test runs using theBIPM standard software for the calculation of UTC, now including SDR TWSTFT data, andstarted to calculate SDR TWSTFT time links as backup from October 2017. The use of SDRTWSTFT in UTC generation will begin in 2018.

Keywords
UTC, TWSTFT, SDR, diurnal, uncertainty, time transfer
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-35175 (URN)10.1088/1681-7575/aacbe6 (DOI)
Available from: 2018-09-12 Created: 2018-09-12 Last updated: 2019-05-29Bibliographically approved
Rieck, C., Jarlemark, P. O. .. & Jaldehag, K. (2017). Utilizing TWSTFT in a passive configuration. In: Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, PTTI: . Paper presented at Precise Time and Time Interval Systems and Applications Meeting, PTTI 2017, 30 January 2017 through 2 February 2017 (pp. 219-234). Institute of Electrical and Electronics Engineers Inc.
Open this publication in new window or tab >>Utilizing TWSTFT in a passive configuration
2017 (English)In: Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, PTTI, Institute of Electrical and Electronics Engineers Inc. , 2017, p. 219-234Conference paper, Published paper (Refereed)
Abstract [en]

In this paper we suggest the passive usage of Two Way Satellite Time and Frequency Transfer (TWSTFT). In a passive configuration a receiver observes, possibly multiple, codes sent by the active users of a TWSTFT-network. Common view observations of the same signals by a pair of observers can be used to compare their local clocks. Similar to GNSS, the users need to know their local coordinates and the orbit of the satellite in order to reduce the measurements by the geometry. As the orbit is usually poorly known, it is essential to establish an infrastructure that provides the users with satellite ephemerides and appropriated correction models. In this initial study we use the ranging measurements performed by the active European network to TELSTAR 11N in order to estimate precise satellite positions. Residual ranges of the position estimates are well below 1 m. Based on the precise satellite positions and other regular TWSTFT measurements an extended Kepler description of the orbit is determined, which can be used to estimate ranges from the satellite to a passive user at arbitrary station positions and arbitrary epochs. A passive use of TWSTFT will enable us to increase the number of measurements without increasing the noise level on the transponder. It will also reach out to a new group of users, both commercial and scientific, which will benefit from current and future developments of TWSTFT. NMIs will be able to offer an independent method for robust distribution of their national time scales. © 2017 Institute of Electrical and Electronics Engineers Inc. All rights reserved.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers Inc., 2017
Keywords
Orbits, Satellites, Time measurement, Correction models, European networks, Local coordinate, Position estimates, Residual range, Satellite ephemeris, Satellite position, Two-way satellite time and frequency transfers, Tracking (position)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:ri:diva-38134 (URN)10.33012/2017.15002 (DOI)2-s2.0-85047020426 (Scopus ID)9781510855397 (ISBN)
Conference
Precise Time and Time Interval Systems and Applications Meeting, PTTI 2017, 30 January 2017 through 2 February 2017
Available from: 2019-03-04 Created: 2019-03-04 Last updated: 2019-08-09Bibliographically approved
Jaldehag, K., Jarlemark, P. & Rieck, C. (2016). Clock models for Kalman filtering.
Open this publication in new window or tab >>Clock models for Kalman filtering
2016 (English)Report (Other academic)
Series
SP Rapport, ISSN 0284-5172 ; 2016:48
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-623 (URN)
Available from: 2016-06-29 Created: 2016-06-29 Last updated: 2018-08-13Bibliographically approved
Hobiger, T., Rieck, C., Rüdiger, H. & Koyama, Y. (2015). Combining GPS and VLBI for inter-continental frequency transfer (ed.). Metrologia, 52(2), 251-261
Open this publication in new window or tab >>Combining GPS and VLBI for inter-continental frequency transfer
2015 (English)In: Metrologia, ISSN 0026-1394, E-ISSN 1681-7575, Vol. 52, no 2, p. 251-261Article in journal (Refereed) Published
Abstract [en]

For decades the global positioning system (GPS) has been the only space geodetic technique routinely used for inter-continental frequency transfer applications. In the past very long baseline interferometry (VLBI) has also been considered for this purpose and the method's capabilities were studied several times. However, compared to GPS current VLBI technology only provides few observations per hour, thus limiting its potential to improve frequency comparisons. We therefore investigate the effect of combining GPS and VLBI on the observation level in order to draw the maximum benefit from the strength of each individual technique. As a test-bed for our study we use the CONT11 campaign observed in 2011. First we review the frequency transfer performance that can be achieved with independent technique-specific analyses, both with individual software packages and with the multitechnique software c5++. With this analysis approach both techniques, GPS and VLBI, show similar frequency link instabilities at the level of 10 -14 to 10 -15 (MDEV) on inter-continental baselines for averaging times of one day. Then we use the c5++ software for a combined analysis of GPS and VLBI data on the observation level. We demonstrate that our combination approach leads to small but consistent improvements for frequency transfer of up to 10%, in particular for averaging periods longer than 3000 s.

Keywords
Combination, Frequency transfer, GPS, Variance component estimation, VLBI
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-6821 (URN)10.1088/0026-1394/52/2/251 (DOI)23616 (Local ID)23616 (Archive number)23616 (OAI)
Available from: 2016-09-08 Created: 2016-09-08 Last updated: 2019-07-02Bibliographically approved
Hedekvist, P. O., Jaldehag, K., Ebenhag, S.-C., Rieck, C., Bideberg, G. & Jaldehag, K. (2013). Time and Frequency Activities at SP. In: : . Paper presented at Proceedings of the 45th Annual Precise Time and Time Interval Systems and Applications Meeting, December 2 - 5, 2013, Hyatt Regency Bellevue, Bellevue, Washington (pp. 21-25).
Open this publication in new window or tab >>Time and Frequency Activities at SP
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2013 (English)Conference paper, Published paper (Other academic)
Abstract [en]

The national Time and Frequency laboratory of Sweden is a part of SP Technical Research Institute of Sweden since 1995. The laboratory is responsible for maintaining the official realization of Swedish standard time and the dissemination of it within Sweden. The objectives of the laboratory include supporting and making it accessible to Swedish industry and authorities with accurate measures of Time and Frequency by instrument calibration, knowledge-transfer, time dissemination, research and development. Swedish standard time is regulated by law to follow UTC as achieved and maintained by the BIPM. The atomic clocks that are used to implement UTC(SP), the realization of UTC in Sweden, are located at five different sites and are reported to TAI using data from TWSTFT and GNSS links. The activities in the Time and Frequency laboratory at SP is presently undergoing an expansion, with the construction of a new additional secure site, the implementation of a distributed time scale and the participation in the Galileo time scale.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:ri:diva-38800 (URN)
Conference
Proceedings of the 45th Annual Precise Time and Time Interval Systems and Applications Meeting, December 2 - 5, 2013, Hyatt Regency Bellevue, Bellevue, Washington
Available from: 2019-05-14 Created: 2019-05-14 Last updated: 2019-05-15Bibliographically approved
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1710-6058

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