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Sökning: WFRF:(Emardson R.) > Chalmers tekniska högskola

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  • Bergstrand, Sten, 1971-, et al. (författare)
  • Ionospheric Corrections for Accurate Positioning in Real Time
  • 2005
  • Ingår i: in Proc. Radio Science and Communication (RVK), eds. O. Gustafsson, P. Löwenborg, Linköping, Sweden, June 14-16, 2005. - 91-7056-122-2 ; s. 391-394
  • Konferensbidrag (övrigt vetenskapligt)
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  • Ebenhag, Sven-Christian, 1976-, et al. (författare)
  • Measurements and Error Sources in Time Transfer Using Asynchronous Fiber Network
  • 2010
  • Ingår i: IEEE Transactions on instrumentation and measurement. - 0018-9456. ; 59:7, s. 1918-1924
  • Tidskriftsartikel (refereegranskat)abstract
    • We have performed time transfer experiments based on passive listening in fiber optical networks using Packet over synchronous optical networking (SONET)/synchronous digital hierarchy(SDH). The experiments have been performed with different complexity and over different distances. For assessment of the results, we have used a GPS link based on carrier-phase observations. On a 560-km link, precision that is relative to the GPS link of < 1 ns has been obtained over several months. In this paper, we describe and quantify the different error sources influencing the fiber time transfer measurements. We show that the temperature dependence of the optical fiber is the major contribution to the error budget, and, thus, reducing this effect should be the best way of improving the results.
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  • Ebenhag, Sven-Christian, 1976-, et al. (författare)
  • TIME TRANSFER USING AN ASYNCHRONOUS COMPUTER NETWORK: RESULTS FROM A 500 KM BASELINE EXPERIMENT
  • 2007
  • Ingår i: Topical Meeting on Precise Time and Time Interval, 27-30/11, Long Beach, CA.
  • Konferensbidrag (refereegranskat)abstract
    • SP Technical Research Institute of Sweden and STUPI have performed a time transfer experiment over a 500km long baseline between Borås and Stockholm. The time transfer technique passively utilizes the data bit stream generated in an optical fiber computer network based on the packet over SONET/SDH technique. A small fraction of the optical signal is monitored both at the transmitter and at the receiver. When an occurrence of a unique bit sequence of the SDH frames is detected, an electrical pulse is generated and compared with a resolution of 100 ps to a local clock. With data from all four positions of an optical bidirectional link, two-way time-transfer can be achieved and any symmetrical variations in delay can potentially be cancelled. The results presented here have been obtained over OptoSUNET, the new Swedish University Network. In the experiment, 10 Gbit/s traffic from SP over OptoSUNET is extended in Stockholm to STUPI, a clock laboratory which is the second node in this setup. This reconnection enables that a communication channel is established between two nodes, with no intermediate jump. The time-transfer experiment includes more than 500 km of fiber transmission, of which several km is via air-lines. By comparing the results from a GPS carrierphase link, a precision better than ± 1 ns is achieved over several months of measurements between two Hydrogen-masers.
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  • Ebenhag, Sven-Christian, 1976-, et al. (författare)
  • Time transfer using an asynchronous computer network: Results from three weeks of measurements
  • 2007
  • Ingår i: European Frequency and Time Forum, 29/5 - 1/6, Geneva, CH.
  • Konferensbidrag (refereegranskat)abstract
    • We have performed a time transfer experiment between two atomic clocks, over a distance of approximately 75 km using an 10 Gbit/s asynchronous fiber-optic computer network. The time transfer was accomplished through passive listening on existing data traffic and a pilot sequence in the SDH bit stream. In order to assess the fiber-link clock comparison, we simultaneously compared the clocks using a GPS carrier phase link. The standard deviation of the difference between the two time transfer links over the three-week time period was 243 ps.
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  • Elgered, Gunnar, 1955-, et al. (författare)
  • Validation of climate models using European ground-based GNSS observations
  • 2009
  • Ingår i: Proc. of 2nd Colloquium Scientific and Fundamental Aspects of the Galileo Programme, European Space Agency, 15-19 October, 2009, Padua, Italy. ; CD ROM
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • We summarize an ongoing research project where we assess the quality of time series of the Integrated Water Vapour in the atmosphere estimated from ground-based GNSS data for the application of validating and possibly improving climate models. The focus is on the factors limiting the accuracy and especially the long-term stability of the GNSS technique.Higher order ionospheric corrections have been studied, using realistic values for the Total Electron Content (TEC) close to the solar maximum in 2002. Averaged over ten days we find that the impact in the mean IWV is less than 0.1 kg/m^2. Another factor is the model used for antenna phase centre variations. We have studied this effect on the IWV estimates by simulations and by studying estimates of the IWV based on observed GPS signals. We find that ignoring satellite antenna phase variations, when processing GPS data from 2003-2008, can significantly influence the values of the estimated linear trends. The value depends on the latitude of the site as well as on the elevation cut-off angle used in the data analysis. Finally, we show a significant correlation between estimated linear trends in the IWV and the corresponding linear trends in the independently observed ground temperature.
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