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- Ebenhag, Sven-Christian, 1976-, et al.
(författare)
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Measurements and Error Sources in Time Transfer Using Asynchronous Fiber Network
- 2010
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Ingår i: IEEE Transactions on instrumentation and measurement. - 0018-9456. ; 59:7, s. 1918-1924
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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. |
- Ebenhag, Sven-Christian, 1976-, et al.
(författare)
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TIME TRANSFER USING AN ASYNCHRONOUS COMPUTER NETWORK: RESULTS FROM A 500 KM BASELINE EXPERIMENT
- 2007
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Ingår i: Topical Meeting on Precise Time and Time Interval, 27-30/11, Long Beach, CA.
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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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| 3. |
- Ebenhag, Sven-Christian, 1976-, et al.
(författare)
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Time transfer using an asynchronous computer network: Results from three weeks of measurements
- 2007
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Ingår i: European Frequency and Time Forum, 29/5 - 1/6, Geneva, CH.
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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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| 6. |
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| 7. |
- Ebenhag, Sven-Christian, 1976-, et al.
(författare)
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Time transfer using an asynchronous computer network: An analysis of error sources
- 2007
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Ingår i: European Frequency and Time Forum, 29/5 - 1/6, Geneva, CH.
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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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| 8. |
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| 9. |
- Emardson, T. Ragne, 1969-
(författare)
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Studies of Atmospheric Water Vapor Using the Global Positioning System
- 1998
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Doktorsavhandling (övrigt vetenskapligt)abstract
- Atmospheric water vapor is of fundamental interest in the Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) techniques. These techniques are based on the timing of radio waves propagating through the atmosphere. The received signals are delayed by the water vapor mainly located in the lower part of the atmosphere called the troposphere. In order to achieve accurate positioning, such effects have to be corrected for. This can be done by estimating the delay from the signals themselves. From these results it is possible to derive the amount of water vapor in the atmosphere. The GPS and VLBI techniques can thus be used both for positioning and for determination of the amount of atmospheric water vapor.<p /> This thesis deals mainly with the technique to estimate the amount of water vapor in the atmosphere with GPS. Modeling of the atmosphere is treated as well as how to convert the signal delay estimates from GPS to the water vapor amount. The results obtained are assessed through comparisons with independent techniques, such as radiosondes and a microwave radiometer.<p /> The results in this thesis show that it is possible to measure the atmospheric water vapor with GPS with an accuracy comparable to techniques presently in use for that purpose. GPS gives, however, a better temporal and spatial resolution as well as being more cost-effective than the present radiosonde launches. This may prove to be useful for the meteorological community, as water vapor is an important factor in numerical weather prediction, and in climate studies since it is one of the most important greenhouse gases. Improved modeling of the water vapor and assessment of the results will also benefit positioning with GPS, which is useful, for example, in the determination of the land uplift after the last glaciation period.
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| 10. |
- Jarlemark, Per O. J., 1962-, et al.
(författare)
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Ground-Based GPS for Validation of Climate Models: The Impact of Satellite Antenna Phase Center Variations
- 2010
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Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892. ; 48:10, s. 3847-3854
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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.
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