Ragne Emardson

Time Transfer by Passive Listening Over a 10-Gb/s Optical Fiber

A technique for time and frequency transfer over an asynchronous fiber optical transmission control protocol (TCP)/IP network is being developed in Sweden by SP Measurement Technology together with STUPI. The technique is based on passive listening to existing data traffic at 10 Gb/s in the network. Since the network is asynchronous, intermediate supporting clocks will be located and compared at each router. We detect, with a specially designed high-speed optoelectronic device, a header recognizer, the frame alignment bytes of the synchronous optical network (SONET)/synchronous digital hierarchy (SDH) protocol, as a reference for the supporting clock comparison. The goal of the project is to establish a time transfer system with an accuracy on the nanosecond level. In this paper, we present the results of a time transfer over a distance of 5 km. We have compared two clocks: a cesium clock at the Swedish National Laboratory for time and frequency and a remote rubidium clock. The results of the time transfer with the fiber link have been simultaneously compared to measurements with a Global Positioning System (GPS) carrier phase link in terms of precision and stability. The root-mean-square (rms) difference between the time difference measured with the fiber link and the GPS link is approximately 300 ps. A large part of the difference is due to the heating of the GPS antenna cable, which introduces daily delay variations on the order of 1 ns from peak to peak. For one of the days with small day-to-day variations in temperature, the corresponding rms difference is 72 ps, and the Allan deviation is below 30 ps for averaging times longer than 5 min.

Measurements and Error Sources in Time Transfer Using Asynchronous Fiber Network

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.

Time and frequency transfer in an asynchronous TCP/IP over SDH-network utilizing passive listening

A technique for time and frequency transfer over an asynchronous TCP/IP network is being developed by SP, Swedish National Testing and Research Institute together with STUPI. When implemented, users will be able to compare their clocks by connecting to the system. The technique is based on passive listening to existing data traffic in the network. Since the network is asynchronous, intermediate clocks are located and compared at each router. We use the frame alignment bytes of the SONET/SDH protocol as references in order to compare these clocks. 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 late 2005

Measurement with Persons:A European Network

Abstract: The European ‘Measuring the Impossible’ Network MINET promotes new research activities in measurement dependent on human perception and/or interpretation. This includes the perceived attributes of products and services, such as quality or desirability, and societal parameters such as security and well-being. Work has aimed at consensus about four ‘generic’ metrological issues: (1) Measurement Concepts & Terminology; (2) Measurement Techniques: (3) Measurement Uncertainty; and (4) Decision-making & Impact Assessment, and how these can be applied specifically to the ‘Measurement of Persons’ in terms of ‘Man as a Measurement Instrument’ and ‘Measuring Man.’ Some of the main achievements of MINET include a research repository with glossary; training course; book; series of workshops; think tanks and study visits, which have brought together a unique constellation of researchers from physics, metrology, physiology, psychophysics, psychology and sociology. Metrology (quality-assured measurement) in this area is relatively underdeveloped, despite great potential for innovation, and extends beyond traditional physiological metrology in that it also deals with measurement with all human senses as well as mental and behavioral processes. This is particularly relevant in applications where humans are an important component of critical systems, where for instance health and safety are at stake.

Overall accessibility to traveling by rail for the elderly with and without functional limitations: the whole-trip perspective

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.

Spatial variability in the ionosphere measured with GNSS networks

Traveling ionospheric disturbances (TIDs) appear as medium-scale TIDs at midlatitudes and as polar cap patches at high latitudes. Both can have a negative impact on Global Navigation Satellite Systems (GNSS) measurements, although the amplitude is of tenths of a total electron content unit (TECU), 1 TECU = 1016 el m2. 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 13 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 nighttime than during daytime, while for central Europe, the variability is larger during daytime. At solar maximum, the variability is larger during the months October and November and smaller in June and July.

Uncertainty Evaluation in Multivariate Analysis – A Test Case Study

We have used different multivariate analysis methods to estimate quantities in the fields of food control and atmospheric remote sensing. In order to estimate the uncertainties in these estimates we studied analytical as well as non-parametric numerical methods. The methods have been evaluated by comparison between obtained results and independent sets of measurements. We present one test case from each field, including results, where these methods have been applied. For the food control test case reduced chi-squared

The MeteoMet project–metrology for meteorology : challenges and results

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