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Träfflista för sökning "WFRF:(Emardson T. Ragne 1969 ) "

Sökning: WFRF:(Emardson T. Ragne 1969 )

  • Resultat 1-10 av 13
  • [1]2Nästa
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1.
  • Ebenhag, Sven-Christian, 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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2.
  • Emardson, Ragne, et al. (författare)
  • Spatial variability in the ionosphere measured with GNSS networks
  • 2013
  • Ingår i: Radio Science. - 0048-6604. ; 48:5, s. 646-652
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
3.
  • Jarlemark, Per O. J., 1962-, et al. (författare)
  • Ground-Based GPS for Validation of Climate Models: The Impact of Satellite Antenna Phase Center Variations
  • 2010
  • Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892. ; 48:10, s. 3847-3854
  • Tidskriftsartikel (refereegranskat)abstract
    • The amount of water vapor in the atmosphere is an important indicator for climate change. Using the Global Positioning System (GPS), it is possible to estimate the integrated water vapor (IWV) above the ground-based GPS receiver. In order to optimally determine the IWV, a correct model of the received signal phase is essential. We have studied the effect of the satellite antenna phase center variations (PCVs) on the IWV estimates by simulating the effect and by studying the estimates of the IWV based on the observed GPS signals. During a period of five years, from 2003 to 2008, a new satellite type was introduced, and it steadily grew in numbers. The antenna PCVs for these satellites deviate from the earlier satellite types and contribute to excess IWV estimates. We find that ignoring satellite antenna phase variations for this time period can lead to an additional IWV trend of about 0.15 kg/m2/year for regular GPS processing.
4.
  • Steinmetz, Erik, et al. (författare)
  • Assessment of GPS derived speed for verification of speed measuring devices
  • 2014
  • Ingår i: Int. J. of Instrumentation Technology. - 2043-7854. ; 1:3, s. 212-227
  • Tidskriftsartikel (refereegranskat)abstract
    • Speed information from GPS is increasingly used and provides an alternative to conventional methods such as wheel speed sensors. We investigate the possibility to use GPS derived speed as a reference when verifying laser and radar-based speed measuring devices used in traffic enforcement. We have set up a realistic test scenario where a GPS equipped vehicle was driven at three different speeds (40, 90 and 130 km/h) through a pre-defined measurement zone. An independent and traceable reference speed was calculated by accurately measuring the length of the measurement zone (approximately 15 metres), and the time it took to pass through it. The reference speed was compared to the average GPS speed for each passage. This comparisons show that the standard uncertainty of such GPS speed measurements is less than 0.05 km/h. Hence, GPS derived speed meets the accuracy requirements for verification of laser and radar based speed measuring devices.
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5.
  • 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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6.
  • 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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7.
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8.
  • Hedekvist, Per Olof, 1967-, et al. (författare)
  • Accurate time transfer utilizing the synchronization in an SDH-network
  • 2006
  • Ingår i: 2006 Optical Fiber Communication Conference, and the 2006 National Fiber Optic Engineers Conference; Anaheim, CA; United States; 5 March 2006 through 10 March 2006. - 978-155752803-2
  • Konferensbidrag (refereegranskat)abstract
    • A nationwide system for accurate time distribution is being developed, utilizing synchronization in an SDH-network. The first experimental results based on this technique are presented, performed on, but not limited to, STM-64.
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9.
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10.
  • Ebenhag, Sven-Christian, 1976-, et al. (författare)
  • Time transfer using an asynchronous computer network: An analysis of error sources
  • 2007
  • Ingår i: European Frequency and Time Forum, 29/5 - 1/6, Geneva, CH.
  • Konferensbidrag (refereegranskat)abstract
    • We have performed a time transfer over a distance of approximately 75 km using an asynchronous computer network based on optical fibers. In order to validate the results from this fiber-link, we have compared the results with a GPS-link, which consists of carrier phase observations. All electronic cabinets were equipped with temperature and humidity sensors. Here we present experiments where the temperature and humidity of the delay in the electrical components were investigated. All components showed some temperature dependence, but no significant humidity dependence was found. By using the derived temperature coefficient for the components the standard deviation of the difference between the fiber link and GPS link decreased from 243ps to184ps.
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