| 1. |
- Bergstrand, Sten, 1971, et al.
(författare)
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Ionospheric Corrections for Accurate Positioning in Real Time
- 2005
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Ingår i: in Proc. Radio Science and Communication (RVK), eds. O. Gustafsson, P. Löwenborg, Linköping, Sweden, June 14-16, 2005. - 9170561222 ; , s. 391-394
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 2. |
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| 3. |
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| 4. |
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| 5. |
- 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. - 1557-9662 .- 0018-9456. ; 59:7, s. 1918-1924
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Tidskriftsartikel (refereegranskat)abstract
- We have performed time transfer experiments basedon passive listening in fiber optical networks using Packet over synchronous optical networking (SONET)/synchronous digital hierarchy(SDH). The experiments have been performed with differentcomplexity and over different distances. For assessmentof 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
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| 6. |
- Ebenhag, Sven-Christian, 1976, et al.
(författare)
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Time Transfer over a 560 km Fiber Link
- 2008
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Ingår i: EFTF 2008 - 22nd European Frequency and Time Forum. ; , s. Paper E5A04 -
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Konferensbidrag (refereegranskat)
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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 ofapproximately 75 km using an asynchronous computer networkbased on optical fibers. In order to validate the results from thisfiber-link, we have compared the results with a GPS-link, whichconsists of carrier phase observations. All electronic cabinetswere equipped with temperature and humidity sensors. Here wepresent experiments where the temperature and humidity of thedelay in the electrical components were investigated. Allcomponents showed some temperature dependence, but nosignificant humidity dependence was found. By using thederived temperature coefficient for the components the standarddeviation of the difference between the fiber link and GPS linkdecreased from 243ps to184ps.
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| 8. |
- 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 transferexperiment over a 500km long baseline between Borås and Stockholm. The time transfertechnique passively utilizes the data bit stream generated in an optical fiber computer networkbased on the packet over SONET/SDH technique. A small fraction of the optical signal ismonitored both at the transmitter and at the receiver. When an occurrence of a unique bitsequence of the SDH frames is detected, an electrical pulse is generated and compared with aresolution of 100 ps to a local clock. With data from all four positions of an optical bidirectionallink, two-way time-transfer can be achieved and any symmetrical variations in delay canpotentially be cancelled. The results presented here have been obtained over OptoSUNET, thenew Swedish University Network. In the experiment, 10 Gbit/s traffic from SP over OptoSUNETis 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 fibertransmission, of which several km is via air-lines. By comparing the results from a GPS carrierphaselink, a precision better than ± 1 ns is achieved over several months of measurementsbetween two Hydrogen-masers.
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| 9. |
- 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 experimentbetween two atomic clocks, over a distance of approximately 75km using an 10 Gbit/s asynchronous fiber-optic computernetwork. The time transfer was accomplished through passivelistening on existing data traffic and a pilot sequence in the SDHbit stream. In order to assess the fiber-link clock comparison, wesimultaneously compared the clocks using a GPS carrier phaselink. The standard deviation of the difference between the twotime transfer links over the three-week time period was 243 ps.
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| 10. |
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| 11. |
- Elgered, Gunnar, 1955, et al.
(författare)
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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
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 12. |
- Emardson, Ragne, 1969, et al.
(författare)
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GROUND- AND SATELLITE- BASED GNSS MEASUREMENTS OF WATER VAPOUR WITH FOCUS ON CLIMATE APPLICATIONS
- 2014
-
Ingår i: Proceedings of Metrology for Meteorology and Climate 2014 conference.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Water vapour is one of the most important green-house gases and the amount of water vapor in the atmosphere is an important indicator for climate change. Due to its high variability, irregular height distribution and poor mixing with other constituents, accurate measurements of water vapour in the atmosphere are difficult and costly to carry out with high temporal and spatial resolution over long time. The delay of Global Navigation Satellite Systems (GNSS) signals when propagating through the atmosphere due to the presence of water vapour is nearly proportional to the quantity of water vapour integrated along the signal path. Hence, using ground-based GNSS receiver networks it is possible to measure the signal delay in the atmosphere, which in turn can be used to derive the atmospheric water vapour content, the Integrated Water Vapour (IWV). Since time interval measurements can be traceable to standards, it is a promising method for providing an observational system for climate monitoring. However, in order to make a proper uncertainty assessment of the measured water vapour, the different error sources affecting the measurements need to be controlled. GNSS occultation measurements are obtained by deploying GNSS receivers onboard Low Earth Orbit (LEO) satellites. The main observable in GNSS occultation measurements is the Doppler shift of the received signal phase. Based on the Doppler shift the vertical profile of the refractive index can be inferred. From the refractive index measurements, we can estimate temperature, pressure, and the amount of water vapour. A key issue in using occultation measurement for climate purposes lies in the methodology of making the measured parameters traceable to references. Here, we present new methods of using booth ground-based and satellite-based GNSS measurements for climate studies. We have used 6 months of GNSS measurements collected both from ground-based networks and from receivers deployed on satellites.
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| 13. |
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| 14. |
- Emardson, Ragne, et al.
(författare)
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Ionospheric Effects on Network-RTK
- 2011
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Rapport (refereegranskat)abstract
- 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.
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| 15. |
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| 16. |
- Emardson, Ragne, et al.
(författare)
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Measurements of accessibility to rail transport systems
- 2011
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Ingår i: International Conference of Advanced Mathematical and Computational Tools in Metrology and Testing (AMCTM).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Improving accessibility to railway systems for persons with disabilities is a governmental assignment to the Swedish Transport Administration. A main issue is to develop quality assured measurement of accessibility. Apart from the accessibility definition, our research focus is on the validity of the measurements and measurement uncertainty. By defining an accessibility measure that is multiplicative, we obtain a measure that represents the different barriers persons can face when travelling.
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| 17. |
- Emardson, Ragne, et al.
(författare)
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Optimering av referensstationskonfiguration
- 2011
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Rapport (refereegranskat)abstract
- Real Time Kinematic (RTK) is a system that uses the Global Navigation Satellite Systems (GNSS) for accurate positioning in real time. The idea of RTK is to receive GNSS signals with a stationary reference at a known position and using these measurements to correct the positioning data for a rover on another site where you want to determine the coordinates. The Swedish National Transport Administration operates the Project “Stomnät i Luften (SIL)”. The project aims to create a national strategy for the RTK-based core network to achieve a more efficient process for the Transport Administration's commitments to construction projects. Within the National SWEPOS network, the distance between reference stations is typically 70 km. For example, at construction work, additional reference stations are deployed around an actual working area. The purpose of this report is to answer three main questions on how performance is affected by the combination of dense and sparse reference networks, how an optimal densification of the reference network should be designed and how accuracy is affected by the construction project spatial scale We show by simulations that the best locations of reference stations to minimize the measurement error is next to the road. A denser network means we can combine large and small triangles in the network. The best measurements are achieved when the inner triangle is given in principle all weight. In practice it may be reasonable to add some weight to even the outer triangle for robustness reasons. For small construction projects, around 5 km, the simulation shows that the vertical measurement error from the RTK system is 3 mm and an expected total vertical measurement error is around 8 mm when including the contribution from the local rover. For large construction projects, about 70 km, the corresponding values are 5 mm and 9 mm respectively For these situations, there is much to gain in accuracy if the installation of the rover can be done in a way that the “local effects”, such as reflections and partial blockage is minimized . The contributions from the local effects will, however, vary greatly depending on the particular position and assembly. For regional construction projects the vertical measurement error from the RTK system is 10 mm and an expected total vertical measurement error is around 12 mm.
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| 18. |
- Emardson, Ragne, et al.
(författare)
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Spatial variability in the ionosphere measured with GNSS networks
- 2013
-
Ingår i: Radio Science. ; 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.
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| 19. |
- Emardson, 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/konstnärligt)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. 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. 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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| 20. |
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| 21. |
- Emardson, Ragne, 1969, et al.
(författare)
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Time and Frequency Transfer in an Asynchronous TCP/IP over SDH-network Utilizing Passive Listening
- 2005
-
Ingår i: IEEE Topical meeting on Precise Time and Time Interval 2005.
-
Konferensbidrag (refereegranskat)abstract
- SP, Swedish National Testing and Research Institute together with STUPI have developed a technique for time and frequency transfer over an asynchronous TCP/IP network. The method is based on passive listening to existing data traffic in the network. We use the frame alignment bytes of the SONET/SDH protocol used between routers as references in order to compare standards located at the routers. As a test bed for the experiment, we will use the Swedish university Computer Network (SUNET). A preliminary assessment of the technique in a lab environment will be performed in late 2005.
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| 22. |
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| 23. |
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| 24. |
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| 25. |
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| 26. |
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| 27. |
- Eriksson, Henrik, et al.
(författare)
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Smartphones as Wireless Reflector Tags?
- 2014
-
Rapport (refereegranskat)abstract
- This report investigates the feasibility of using smartphones as wireless reflector tags. A smartphone communicates its GNSS positioning data via peer-to-peer connections to nearby road users to notify its presence. Appropriate use cases are studied based on accident data. Different communication protocols and a pseudo differencing positioning technique are evaluated. Possibilities and obstacles are presented.
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| 28. |
- Hedekvist, Per Olof E, 1967, et al.
(författare)
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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. - 9781557528032 ; 2006
-
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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| 29. |
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| 30. |
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| 31. |
- Jarlemark, Per, et al.
(författare)
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Error Sources in Network RTK
- 2011
-
Ingår i: Proceedings of the 24th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS 2011).
-
Konferensbidrag (refereegranskat)abstract
- 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
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| 32. |
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| 33. |
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| 34. |
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| 35. |
- Jarlemark, Per, et al.
(författare)
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Measurement accuracy in Network-RTK
- 2010
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Ingår i: Bolletino di Geodesia e Scienze Affini. ; 69, s. 2-3
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 36. |
- 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
-
Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 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.
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| 37. |
- Merlone, A., et al.
(författare)
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The MeteoMet project - metrology for meteorology: challenges and results
- 2015
-
Ingår i: Meteorological Applications. - : Wiley. - 1350-4827 .- 1469-8080. ; 22, s. 820-829
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 38. |
- Ning, Tong, 1975, et al.
(författare)
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High-Rate GNSS Techniques for the Detection of Large Seismic Displacements
- 2009
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Ingår i: the IEEE International Geoscience and Remote Sensing Symposium (IGARSS). ; , s. V 359-362
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Detection of the seismic strong motion is of great importancefor earthquake studies. We have investigated the usageof high-rate sampled Global Navigation Satellite System(GNSS) data to measure seismic motion by implementingan industrial robot simulating the displacements close to anearthquake. The motion of the robot is tracked by GlobalPositioning System (GPS) signals. Two baselines-400 m and60 km-from the robot to reference stations are used to processthe observed GPS data. Both methods give similar (within0.5 mm) Root Mean Square (RMS) differences between theestimated and the commanded coordinates. The RMS differencesare approximately 3.5 mm in the east component, 5 mmin the north component, and 7 mm in the vertical component.
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| 39. |
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| 40. |
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| 41. |
- Pendrill, Leslie, et al.
(författare)
-
Psychometric measurement and decision-making of accessibilityin public transport for older persons with functional limitations
- 2014
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Vulnerable travellers face challenges in the transport environment potentially leading to decreased mobility. A research goal is to find out how to improve railway accessibility by reducing barriers for persons with functional limitations. A method for measuring accessibility has earlier been developed where travel barriers are assigned different weights based on persons’ functional ability and travel behaviour. The more weight placed on a certain barrier, the less accessible and thus less probable a particular journey will be. In the present work, these travel-barrier weights are analysed psychometrically based on the replies to questions about ease or difficulty of accessing travel with various barriers in responses given by 162 older long-distance travellers. An invariant measure theory approach (Rasch) is employed that allows (i) transformation of ordinal questionnaire data onto a quantitative interval scale; and (ii) separate measures of barrier level of challenge and person capability. A principal component analysis revealed three main clusters: 1) mainly ergonomically related questions; 2) mainly informational/cognitive; while cluster 3) is a mix of these two. Correlations are investigated between perceived accessibility and functional ability, and between person capability and functional ability. Independent sources of measurement uncertainty (e.g. under-estimation of scores) are distinguished from separate estimates of task challenge and individual travel capability. These independent sources are accounted for in estimates of reliability and validity of the various measures.
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| 42. |
- Steinmetz, Erik, et al.
(författare)
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Collision-Aware Communication for Intersection Management of Automated Vehicles
- 2018
-
Ingår i: IEEE Access. - 2169-3536. ; 6, s. 77359-77371
-
Tidskriftsartikel (refereegranskat)abstract
- Intersection management of automated vehicles relies on wireless communication, whereby communication resources should be allocated to vehicles while maintaining safety. We present a collision-aware resource allocation (CARA) strategy for coordination of automated and connected vehicles by a centralized intersection manager. The proposed strategy is based on a self-triggered approach and proactively reduces the risk of channel congestion by only assigning communication resources to vehicles that are in critical configurations, i.e., when there is a risk for a future collision. Compared with collision-agnostic communication strategies, typically considered for automated intersection management, the CARA strategy aims to bridge the gap between control, sensing, and communication. It is shown to significantly reduce the required amount of communication (albeit with a slight increase in the control cost), without compromising safety. Furthermore, control cost can be reduced by allowing more frequent communication, which we demonstrate through a trade-off analysis between control performance and communication load. Hence, CARA can operate in communication-limited scenarios, but also be modified for scenarios where the control cost is of primary interest.
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| 43. |
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| 44. |
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| 45. |
- Steinmetz, Erik M, 1984, et al.
(författare)
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Assessment of GPS derived speed for verification of speed measuring devices
- 2014
-
Ingår i: Int. J. of Instrumentation Technology. - 2043-7862. ; 1, 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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| 46. |
- Steinmetz, Erik, et al.
(författare)
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Theoretical Limits on Cooperative Positioning in Mixed Traffic
- 2019
-
Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers Inc.. - 2169-3536. ; 7, s. 49712-49725
-
Tidskriftsartikel (refereegranskat)abstract
- A promising solution to meet the demands on accurate positioning and real-time situational awareness in future intelligent transportation systems (ITSs) is cooperative positioning, where vehicles share sensor information over the wireless channel. However, the sensing and communication technologies required for this will be gradually introduced into the market, and it is, therefore, important to understand what performance we can expect from cooperative positioning systems as we transition to a more modern vehicle fleet. In this paper, we study what effects a gradual market penetration has on cooperative positioning applications, through a Fisher information analysis. The simulation results indicate that solely introducing a small fraction of automated vehicles with high-end sensors significantly improves the positioning quality but is not enough to meet the stringent demands posed by safety critical ITS applications. Furthermore, we find that retrofitting vehicles with low-cost satellite navigation receivers and communication have marginal impact when the positioning requirements are stringent and that the longitudinal road position can be estimated more accurately than lateral. © 2013 IEEE.
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| 47. |
- Sundling, Catherine, et al.
(författare)
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Measurements of perception : Accessability to railway transport system for travelers with and without functional limitations
- 2011
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Ingår i: Metrologie 2011. - Paris, France : Collège Francais de Métrologie. ; , s. 1-6
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- New methods are developed to measure the extent to which rail passengers, especially those with functional limitations, can access transport systems as a part of the whole trip. Measurement with persons is central in determining interdisciplinary commonalities and differences in (i) terminology; (ii) measurement methods; (iii) measurement uncertainty, and (iv) decision making. Metrological concepts are adapted in novel ways to be able to measure the constructs accessibility and usability in railway transport systems for travelers with and without functional limitations. A multiplicative accessibility measure is defined that represents the different barriers persons can face when travelling. Our first action concerns the measurement of measure improvement actions to the railway system and travel.
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| 48. |
- Sundling, Catherine, et al.
(författare)
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New perspective on the accessibility of railway transport for the vulnerable traveller
- 2013
-
Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 459:1
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Tidskriftsartikel (refereegranskat)abstract
- Vulnerable travellers experience various problems in the transport environment. These may reduce public travel confidence and consequently lead to decreased mobility. A goal of our research is to find out how to improve the accessibility to railway travelling, especially, for persons with functional limitations. By reducing barriers, the ability of travelling would be improved, and consequently allow for more flexible travel behaviors. In order to develop a model and a method of measurement for accessibility, we (a) constructed a reference group of representative ‘typical older persons’ (65-85 years) from questionnaire data, and (b) developed an accessibility measure for persons with functional limitations. In this measure barriers have different weights for the different persons depending on their functional ability and travel behavior. This gives the probability of facing a certain barrier when travelling to a certain destination; that is, a measure of accessibility for the individual. The more weight placed on a certain barrier, the less probable it is that the particular journey will take place. These weights will be obtained in forthcoming research on the perception of a set of various travel scenarios representing barriers.
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| 49. |
- Sundling, Catherine, 1962-
(författare)
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Overall Accessibility of Public Transport for Older Adults
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is based on four studies that explore accessibility for older adults during whole trips by public transport. The overall goal was to gain knowledge of the interrelationships among key variables and to develop a conceptual model of the overall accessibility of public transport. More specifically, the research goals were: (a) to explore links among the key variables postulated to be involved in overall accessibility and to explore the links between these variables and railway accessibility; (b) to gain a deeper understanding of links between critical incidents in traveling and travel behavior decisions; and (c) to develop a conceptual model of overall accessibility. The key variables contributing to overall accessibility are functional ability (depending partly on the person’s functional limitation or disease), travel behavior, and barriers encountered during whole-trip traveling involving train. Respondents with more than one functional limitation or disease reported lower functional ability than did those with only one such limitation and respondents with low functional ability were less frequent travelers than were those with high functional ability. Frequent travelers reported railway accessibility to be better than did those who traveled less frequently. The main barriers were ticket cost and poor punctuality, but respondents with the lowest functional ability attributed the barriers encountered to their own health. The critical incidents most frequently reported were found in the categories “physical environment onboard vehicles” and “physical environment at stations or stops”, as well as in the “pricing and planning during ticketing” phase of the trip. Five themes of reactions to critical incidents were identified that had resulted in behavior change: firm restrictions, unpredictability, unfair treatment, complicated trips, and earlier adverse experiences. A conceptual model of overall accessibility was developed, grounded in the empirical research results. This model is summarized in the following propositions: Overall accessibility is a reciprocal relationship among the barriers/facilitators encountered, functional ability, and travel behavior. Accessibility emerges in the person–environment interaction. To understand accessibility, past experiences and future expectations should both be considered, because both will guide travel decisions.
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| 50. |
- Sundling, Catherine, et al.
(författare)
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Overall Accessibility to Traveling by Rail for the Elderly with and without Functional Limitations : The Whole-Trip Perspective
- 2014
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Ingår i: International Journal of Environmental Research and Public Health. - : MDPI AG. - 1661-7827 .- 1660-4601. ; 11:12, s. 12938-12968
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Tidskriftsartikel (refereegranskat)abstract
- Elderly persons’ perceived accessibility to railway traveling depends on their functional limitations/diseases, their functional abilities and their travel behaviors in interaction with the barriers encountered during whole trips. A survey was conducted on a random sample of 1000 city residents (65–85 years old; 57% response rate). The travels were perceived least accessible by respondents with severely reduced functional ability and by those with more than one functional limitation/disease (e.g., restricted mobility and chronic pain). Those who traveled “often”, perceived the accessibility to be better than those who traveled less frequently. For travelers with high functional ability, the main barriers to more frequent traveling were travel costs and low punctuality. For those with low functional ability, one’s own health was reported to be the main barrier. Our results clarify the links among existing functional limitations/functional abilities, the barriers encountered, the travel behavior, and the overall accessibility to traveling. By operationalizing the whole-trip concept as a chain of events, we deliver practical knowledge on vulnerable groups for decision-making to improve the transport environment for all.
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