Per Jarlemark - Academia.edu (original) (raw)

Papers by Per Jarlemark

Research paper thumbnail of Time and frequency transfer in an optical fiber network: First results

A technique for time and frequency transfer over an asynchronous fiber-optical TCP/IP network is ... more A technique for time and frequency transfer over an asynchronous fiber-optical 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 Gbit/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 Header Recogniser high-speed optoelectronic device the frame alignment bytes of the SONET/SDH protocol as references for the supporting clock comparison. The goal of the project is to establish a time transfer system with a precision on the ns level. We have performed an assessment of the technique in a lab environment. The root mean square (rms) difference between the values measured with the fiber network technique and using GPS phase observations is approximately 40 ps. Hence, we conclude that the noise contribution from the hardware will not be a limiting factor in the...

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Research paper thumbnail of Analysis of Temporal and Spatial Variations in Atmospheric Water Vapor Using Microwave Radiometry

The amount of atmospheric water vapor is highly variable in both time and space. In this thesis s... more The amount of atmospheric water vapor is highly variable in both time and space. In this thesis some aspects of the variations in the atmospheric water vapor are treated. Short term variations of up to approximately a day in the radio propagation delay due to water vapor has an ...

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Research paper thumbnail of Microwave radiometry for studies of variations in atmospheric water vapor and cloud liquid content

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Research paper thumbnail of A novel approach using parallel Kalman filters in time and frequency estimation

PAMM, 2007

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Research paper thumbnail of Atmospheric modelling in GPS analysis and its effect on the estimated geodetic parameters

Journal of Geodesy, 1999

. Permanently operating Global Positioning System (GPS) receivers are used today, for example, ... more . Permanently operating Global Positioning System (GPS) receivers are used today, for example, in precise positioning and determination of atmospheric water vapour content. The GPS signals are delayed by various gases when traversing the atmosphere. The delay due to water vapour, the wet delay, is difficult to model using ground surface data and is thus often estimated from the GPS

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Research paper thumbnail of Measurements and Error Sources in Time Transfer Using Asynchronous Fiber Network

IEEE Transactions on Instrumentation and Measurement, 2000

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Research paper thumbnail of Time Transfer by Passive Listening Over a 10-Gb/s Optical Fiber

IEEE Transactions on Instrumentation and Measurement, 2000

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Research paper thumbnail of Time and frequency transfer in an optical fiber network: First results

A technique for time and frequency transfer over an asynchronous fiber-optical TCP/IP network is ... more A technique for time and frequency transfer over an asynchronous fiber-optical 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 Gbit/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 Header Recogniser high-speed optoelectronic device the frame alignment bytes of the SONET/SDH protocol as references for the supporting clock comparison. The goal of the project is to establish a time transfer system with a precision on the ns level. We have performed an assessment of the technique in a lab environment. The root mean square (rms) difference between the values measured with the fiber network technique and using GPS phase observations is approximately 40 ps. Hence, we conclude that the noise contribution from the hardware will not be a limiting factor in the...

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Research paper thumbnail of A fiber based frequency distribution system with enchanced output phase stability

2009 IEEE International Frequency Control Symposium Joint with the 22nd European Frequency and Time forum, 2009

ABSTRACT Experimental results on the stability of the output phase of a frequency distribution sy... more ABSTRACT Experimental results on the stability of the output phase of a frequency distribution system from several days of measurement is presented, in addition to a discussion regarding the influence of control loop parameters. The setup handles the issue that the output phase stability of a system depends on perturbations along the transmission length. This is especially critical if the signal is transmitted through optical fiber, at lengths of a few 100 m. An experimental evaluation using a laser based transmitter at a wavelength of 850 nm, and 625 m of multimode fiber where 575 m where placed outdoor, a temperature dependence of 100 ps/degC was detected. To compensate for these slow variations in real time, a setup using two-way transmission, in conjunction with an adjustable optical delay, was constructed. This device is adjusted to induce a delay variation of equal magnitude but opposite direction, in comparison to the delay change of the fiber. Calculating the modified Allan deviation of the transmitted signal, it is apparent that without active compensation, the deviation at tau below 1000 s is comparable to the values from the measurement system without transmission. At longer integration times, however, the slow variations in the fiber transmission will deteriorate the modified ADEV substantially. When activating the dynamic adjustment of pre-delay in the system, the deviation at shorter times will increase with a few dB, however, the modified ADEV decreases continuously with tau, eventually below the values for the uncompensated system. In conclusion, activating a dynamically controlled pre-delay in a fiber based frequency transmission system will induce a small penalty on fast variations of the output phase, however giving a remarkable improvement on slower variations. The usefulness of this added functionality must therefore be determined by the application of the signal.

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

Proceedings of the 2005 IEEE International Frequency Control Symposium and Exposition, 2005., 2005

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Research paper thumbnail of Time transfer using an asynchronous computer network: An analysis of error sources

2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum, 2007

We have performed a time transfer experiment between two atomic clocks, over a distance of approx... more 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

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Research paper thumbnail of Uncertainty Evaluation in Multivariate Analysis – A Test Case Study

Journal of Mathematical Modelling and Algorithms, 2005

We have used different multivariate analysis methods to estimate quantities in the fields of food... more 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

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Research paper thumbnail of Thermal influence on the receiver chain of GPS carrier phase equipment for time and frequency transfer

IEEE International Frequency Control Sympposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 2003. Proceedings of the 2003, 2000

ABSTRACT In this study a temperature controlled environment is used in order to quantify the ther... more ABSTRACT In this study a temperature controlled environment is used in order to quantify the thermal influence on all major parts of state of the art geodetic GPS receiving equipment. Temperature variations, effective as time delay variations, were identified as a dominating error source that degrades the capabilities of carrier phase GPS based time and frequency transfer considerably. For purely code-based measurements with uncertainties in the ns range is temperature rarely an issue. In contrast carrier phase observations offer potentially a two orders of magnitude better accuracy and are therefore suitable for exploiting the characteristics of maser quality clocks. However, the stability of the environment around the receiver equipment defines the achievable accuracy. Four distinct parts of the receiver chain were subject to systematic measurements of the temperature-delay dependency: antenna preamplifier, antenna and clock cables, power distribution devices and geodetic receivers. A temperature controllable climate chamber was deployed with the respective component to follow a long time-constant temperature stepping. Signal through devices were mainly tested in a vector-voltmeter approach. Zero base line GPS processing was used to test receivers. With individual component temperature dependence being far above the expected accuracy of carrier phase based time and frequency transfer it underlines the necessity to include temperature as an important parameter into time/frequency solutions.

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Research paper thumbnail of First results of real-time time and frequency transfer using GPS code and carrier phase observations

IEEE International Frequency Control Sympposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 2003. Proceedings of the 2003, 2000

ABSTRACT We have used code and carrier phase data from the global positioning system (GPS) satell... more ABSTRACT We have used code and carrier phase data from the global positioning system (GPS) satellites to estimate time differences between atomic clocks in near (<10 s) real-time. For some sites we have used data transmitted via Internet connections and TCP/IP, while for other sites data were collected in deferred time, but processed by a Kalman filter-based software as if they were available in real time. Satellite orbit and clock data of different quality have been used. The real-time estimates of time differences of the station clocks have been compared to those estimated from regular postprocessing using accurate satellite orbits and clocks from the international GPS service (IGS). First results show that the standard deviation of the differences between the real-time carrier phase-based and the postprocessing estimates of the clock time differences can be less than 100 ps for baselines of about 1000 km.

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Research paper thumbnail of A GPS carrier-phase aided clock transport for the calibration of a regional distributed time scale

2009 IEEE International Frequency Control Symposium Joint with the 22nd European Frequency and Time forum, 2009

ABSTRACT Clock transportation is a historically proven time transfer method for the calibration o... more ABSTRACT Clock transportation is a historically proven time transfer method for the calibration of time links and time scales. With the establishment of satellite-based time transfer methods, however, clock transportation has become less attractive especially on long baselines. In order to match for instance the GPS common view time transfer method with calibration uncertainties of a few nanoseconds, it is necessary to transport high quality, expensive clocks such as caesium beam frequency standards. The stability of the clock during transportation and the duration of the transport set the limit of the prediction uncertainty. Being able to measure the clock during transportation instead of predicting it would yield some major advantages: (a) the use of less expensive and small clocks such as rubidium or quartz oscillators for transportation, (b) no need for environmental conditioning of the transported clock, and (c) the duration of the transport is not critical as long as the clock can continuously be measured. One solution to the clock measurement problem during transport is the use of GPS carrier-phase observations as described and evaluated in this paper. It is shown that a calibration uncertainty of less than one nanosecond is potentially achievable.

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Research paper thumbnail of Continuous Real-Time GPS Carrier Phase Based Frequency Transfer on Medium

2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum, 2007

... Technology SP Technical Research Institute of Sweden Box 857, S-501 15 Borås, Sweden {carsten... more ... Technology SP Technical Research Institute of Sweden Box 857, S-501 15 Borås, Sweden {carsten.rieck, per.jarlemark, kenneth.jaldehag}@sp.se ... with slippage between the pulleys, can a fixed ambiguity solution be described with the characteristics of a locked pinion gear. ...

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Research paper thumbnail of Ground-Based GPS Tomography of Water Vapor : Analysis of Simulated and Real Data (3.Application of GPS Data to Atmospheric Science)

Journal of the Meteorological Society of Japan Ser Ii, Mar 25, 2004

ABSTRACT We present the concept, some of the approaches used, and the capabilities of the techniq... more ABSTRACT We present the concept, some of the approaches used, and the capabilities of the technique referred to as GPS tomography. It is used for retrieval of the 3-dimensional distribution of the refractivity due to atmospheric water vapor. We discuss the presently used methods for retrieval of the primary observable in the GPS tomography, the slant path delay, as well as their shortcomings. Comparisons of GPS slant delays to independent data from a microwave radiometer are included. From a tomographic point of view we concentrate on the capabilities to retrieve the vertical structure of the wet refractivity. For this purpose we present and apply two methods for tomographic inversion. Both are based on the Kalman filtering technique, where the expected statistical behavior of the refractivity is utilized. The difference between the two is in the way the covariance matrix of the Kalman filter is constructed. We base our study on simulated and real data from the ground network of 8 GPS receivers operating in Goteborg, Sweden. The results demonstrate that at present the limitations of the GPS tomographic technique are errors in the retrieved wet slant delays and their poor geometric distribution.

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Research paper thumbnail of GPS Tomography: First Results From A Permanent Local Network

We will draw attention to a new technique for retrieval of water vapor fields, which is based on ... more We will draw attention to a new technique for retrieval of water vapor fields, which is based on the use of a small network of GPS receivers, and is referred to as GPS tomography. A subset of the inverse theory utilizing the integrated values of the field distribution is called tomography. To demonstrate the technique we use a permanent local GPS network consisting of 8 stations and located in the G"{o}teborg area (Swe- den). Its baselines range from a few to 15 km. Tomographic results from this network are derived by applying a tomographic method on the measured slant delay values at each site. The method is implemented in the software package LOTTOS (LOcal Tropospheric Tomographic SOftware developed by Alejandro Flores) and is able to produce a tomographic solution of the water vapor induced refractivity in the tropo- sphere. In tropospheric tomography the slant delay values are obtained by combining the estimated zenith delay values with the horizontal gradients. The geometry using GPS is somewhat restricted compared to the classical tomographic approaches where one can choose the direction of the scanning rays. In the case of GPS tomography, we are limited by the satellite constellation and therefore in certain areas of the field that we want to reconstruct some "information gaps" will be present. In order to reduce these uncertainties, additional vertical and horizontal constraints should be included in the solution. Other ways of increasing the information could be: optimization of tomographic grid used, inclusion of more GPS stations and/or additional independent data from GLONASS, GALILEO (in the future), GPS occultation receivers, radioson- des or scanning pointed water vapor radiometers (WVR). We first present simulations of a tomographic solution based on our particular site distribution, sensitivity analyses of the network, as well as some grid optimization results. Impact of GLONASS data inclusion on the water vapor zenith and gradient estimates is studied by comparisons to a WVR. First comparisons of the tomographic results using real data with results from measurements from radiosondes launched in the vicinity the GPS network are also presented. The achievable time resolution of the obtained refractivity profiles can be from some minutes to hours depending on the data availability and the vertical spatial resolution used, which we set to vary within few hundreds of meters.

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Research paper thumbnail of Site-Dependent Electromagnetic Effects in High-Accuracy Applications of GNSS

Agu Fall Meeting Abstracts, Dec 1, 2008

Global Navigation Satellite Systems, GNSS are used in many applications demanding millimetre-leve... more Global Navigation Satellite Systems, GNSS are used in many applications demanding millimetre-level accuracy in positioning. Such applications include monitoring of crustal movements. The GNSS technique also facilitates estimates of the tropospheric water vapour content, an important parameter in numerical weather predictions and climate research. The accuracy of estimated parameters is however degraded by many error sources. Some of those are related to the satellite system and the ground-based receivers. During 2006 the International GNSS Service, IGS implemented absolute antenna calibration for both satellite antennas and the different antenna types used at the ground-based stations. The use of such calibration values improves the accuracy as antenna type related errors are mitigated. However, unmodeled error sources still remain since a antenna couples electromagnetically with its surrounding environment. The absolute antenna calibrations, to be implemented by the IGS, will however not compensate for site- dependent effects. To further improve the accuracy, the site-dependent effects and their dependency on the direction of the observation need to be identified and removed in the GNSS data analysis. In this presentation the site-dependent error sources have been studied for the stations in the Swedish permanent GNSS network, SWEPOS, as well as some stations in the global IGS network. Strong similarities in terms of site-dependent effects were found. Differences in the site characteristics, caused by multipath and different antenna surroundings imply that an individual calibration of each station may be required needed. We have developed and evaluated two different methods for calibration of site dependent effects.

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Research paper thumbnail of Media calibration system for deep space missions: preliminary design and technical aspects

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Research paper thumbnail of Time and frequency transfer in an optical fiber network: First results

A technique for time and frequency transfer over an asynchronous fiber-optical TCP/IP network is ... more A technique for time and frequency transfer over an asynchronous fiber-optical 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 Gbit/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 Header Recogniser high-speed optoelectronic device the frame alignment bytes of the SONET/SDH protocol as references for the supporting clock comparison. The goal of the project is to establish a time transfer system with a precision on the ns level. We have performed an assessment of the technique in a lab environment. The root mean square (rms) difference between the values measured with the fiber network technique and using GPS phase observations is approximately 40 ps. Hence, we conclude that the noise contribution from the hardware will not be a limiting factor in the...

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Research paper thumbnail of Analysis of Temporal and Spatial Variations in Atmospheric Water Vapor Using Microwave Radiometry

The amount of atmospheric water vapor is highly variable in both time and space. In this thesis s... more The amount of atmospheric water vapor is highly variable in both time and space. In this thesis some aspects of the variations in the atmospheric water vapor are treated. Short term variations of up to approximately a day in the radio propagation delay due to water vapor has an ...

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Research paper thumbnail of Microwave radiometry for studies of variations in atmospheric water vapor and cloud liquid content

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A novel approach using parallel Kalman filters in time and frequency estimation

PAMM, 2007

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Atmospheric modelling in GPS analysis and its effect on the estimated geodetic parameters

Journal of Geodesy, 1999

. Permanently operating Global Positioning System (GPS) receivers are used today, for example, ... more . Permanently operating Global Positioning System (GPS) receivers are used today, for example, in precise positioning and determination of atmospheric water vapour content. The GPS signals are delayed by various gases when traversing the atmosphere. The delay due to water vapour, the wet delay, is difficult to model using ground surface data and is thus often estimated from the GPS

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Measurements and Error Sources in Time Transfer Using Asynchronous Fiber Network

IEEE Transactions on Instrumentation and Measurement, 2000

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Research paper thumbnail of Time Transfer by Passive Listening Over a 10-Gb/s Optical Fiber

IEEE Transactions on Instrumentation and Measurement, 2000

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Research paper thumbnail of Time and frequency transfer in an optical fiber network: First results

A technique for time and frequency transfer over an asynchronous fiber-optical TCP/IP network is ... more A technique for time and frequency transfer over an asynchronous fiber-optical 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 Gbit/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 Header Recogniser high-speed optoelectronic device the frame alignment bytes of the SONET/SDH protocol as references for the supporting clock comparison. The goal of the project is to establish a time transfer system with a precision on the ns level. We have performed an assessment of the technique in a lab environment. The root mean square (rms) difference between the values measured with the fiber network technique and using GPS phase observations is approximately 40 ps. Hence, we conclude that the noise contribution from the hardware will not be a limiting factor in the...

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Research paper thumbnail of A fiber based frequency distribution system with enchanced output phase stability

2009 IEEE International Frequency Control Symposium Joint with the 22nd European Frequency and Time forum, 2009

ABSTRACT Experimental results on the stability of the output phase of a frequency distribution sy... more ABSTRACT Experimental results on the stability of the output phase of a frequency distribution system from several days of measurement is presented, in addition to a discussion regarding the influence of control loop parameters. The setup handles the issue that the output phase stability of a system depends on perturbations along the transmission length. This is especially critical if the signal is transmitted through optical fiber, at lengths of a few 100 m. An experimental evaluation using a laser based transmitter at a wavelength of 850 nm, and 625 m of multimode fiber where 575 m where placed outdoor, a temperature dependence of 100 ps/degC was detected. To compensate for these slow variations in real time, a setup using two-way transmission, in conjunction with an adjustable optical delay, was constructed. This device is adjusted to induce a delay variation of equal magnitude but opposite direction, in comparison to the delay change of the fiber. Calculating the modified Allan deviation of the transmitted signal, it is apparent that without active compensation, the deviation at tau below 1000 s is comparable to the values from the measurement system without transmission. At longer integration times, however, the slow variations in the fiber transmission will deteriorate the modified ADEV substantially. When activating the dynamic adjustment of pre-delay in the system, the deviation at shorter times will increase with a few dB, however, the modified ADEV decreases continuously with tau, eventually below the values for the uncompensated system. In conclusion, activating a dynamically controlled pre-delay in a fiber based frequency transmission system will induce a small penalty on fast variations of the output phase, however giving a remarkable improvement on slower variations. The usefulness of this added functionality must therefore be determined by the application of the signal.

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

Proceedings of the 2005 IEEE International Frequency Control Symposium and Exposition, 2005., 2005

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Research paper thumbnail of Time transfer using an asynchronous computer network: An analysis of error sources

2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum, 2007

We have performed a time transfer experiment between two atomic clocks, over a distance of approx... more 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

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Uncertainty Evaluation in Multivariate Analysis – A Test Case Study

Journal of Mathematical Modelling and Algorithms, 2005

We have used different multivariate analysis methods to estimate quantities in the fields of food... more 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

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Research paper thumbnail of Thermal influence on the receiver chain of GPS carrier phase equipment for time and frequency transfer

IEEE International Frequency Control Sympposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 2003. Proceedings of the 2003, 2000

ABSTRACT In this study a temperature controlled environment is used in order to quantify the ther... more ABSTRACT In this study a temperature controlled environment is used in order to quantify the thermal influence on all major parts of state of the art geodetic GPS receiving equipment. Temperature variations, effective as time delay variations, were identified as a dominating error source that degrades the capabilities of carrier phase GPS based time and frequency transfer considerably. For purely code-based measurements with uncertainties in the ns range is temperature rarely an issue. In contrast carrier phase observations offer potentially a two orders of magnitude better accuracy and are therefore suitable for exploiting the characteristics of maser quality clocks. However, the stability of the environment around the receiver equipment defines the achievable accuracy. Four distinct parts of the receiver chain were subject to systematic measurements of the temperature-delay dependency: antenna preamplifier, antenna and clock cables, power distribution devices and geodetic receivers. A temperature controllable climate chamber was deployed with the respective component to follow a long time-constant temperature stepping. Signal through devices were mainly tested in a vector-voltmeter approach. Zero base line GPS processing was used to test receivers. With individual component temperature dependence being far above the expected accuracy of carrier phase based time and frequency transfer it underlines the necessity to include temperature as an important parameter into time/frequency solutions.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of First results of real-time time and frequency transfer using GPS code and carrier phase observations

IEEE International Frequency Control Sympposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 2003. Proceedings of the 2003, 2000

ABSTRACT We have used code and carrier phase data from the global positioning system (GPS) satell... more ABSTRACT We have used code and carrier phase data from the global positioning system (GPS) satellites to estimate time differences between atomic clocks in near (<10 s) real-time. For some sites we have used data transmitted via Internet connections and TCP/IP, while for other sites data were collected in deferred time, but processed by a Kalman filter-based software as if they were available in real time. Satellite orbit and clock data of different quality have been used. The real-time estimates of time differences of the station clocks have been compared to those estimated from regular postprocessing using accurate satellite orbits and clocks from the international GPS service (IGS). First results show that the standard deviation of the differences between the real-time carrier phase-based and the postprocessing estimates of the clock time differences can be less than 100 ps for baselines of about 1000 km.

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Research paper thumbnail of A GPS carrier-phase aided clock transport for the calibration of a regional distributed time scale

2009 IEEE International Frequency Control Symposium Joint with the 22nd European Frequency and Time forum, 2009

ABSTRACT Clock transportation is a historically proven time transfer method for the calibration o... more ABSTRACT Clock transportation is a historically proven time transfer method for the calibration of time links and time scales. With the establishment of satellite-based time transfer methods, however, clock transportation has become less attractive especially on long baselines. In order to match for instance the GPS common view time transfer method with calibration uncertainties of a few nanoseconds, it is necessary to transport high quality, expensive clocks such as caesium beam frequency standards. The stability of the clock during transportation and the duration of the transport set the limit of the prediction uncertainty. Being able to measure the clock during transportation instead of predicting it would yield some major advantages: (a) the use of less expensive and small clocks such as rubidium or quartz oscillators for transportation, (b) no need for environmental conditioning of the transported clock, and (c) the duration of the transport is not critical as long as the clock can continuously be measured. One solution to the clock measurement problem during transport is the use of GPS carrier-phase observations as described and evaluated in this paper. It is shown that a calibration uncertainty of less than one nanosecond is potentially achievable.

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Research paper thumbnail of Continuous Real-Time GPS Carrier Phase Based Frequency Transfer on Medium

2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum, 2007

... Technology SP Technical Research Institute of Sweden Box 857, S-501 15 Borås, Sweden {carsten... more ... Technology SP Technical Research Institute of Sweden Box 857, S-501 15 Borås, Sweden {carsten.rieck, per.jarlemark, kenneth.jaldehag}@sp.se ... with slippage between the pulleys, can a fixed ambiguity solution be described with the characteristics of a locked pinion gear. ...

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Research paper thumbnail of Ground-Based GPS Tomography of Water Vapor : Analysis of Simulated and Real Data (3.Application of GPS Data to Atmospheric Science)

Journal of the Meteorological Society of Japan Ser Ii, Mar 25, 2004

ABSTRACT We present the concept, some of the approaches used, and the capabilities of the techniq... more ABSTRACT We present the concept, some of the approaches used, and the capabilities of the technique referred to as GPS tomography. It is used for retrieval of the 3-dimensional distribution of the refractivity due to atmospheric water vapor. We discuss the presently used methods for retrieval of the primary observable in the GPS tomography, the slant path delay, as well as their shortcomings. Comparisons of GPS slant delays to independent data from a microwave radiometer are included. From a tomographic point of view we concentrate on the capabilities to retrieve the vertical structure of the wet refractivity. For this purpose we present and apply two methods for tomographic inversion. Both are based on the Kalman filtering technique, where the expected statistical behavior of the refractivity is utilized. The difference between the two is in the way the covariance matrix of the Kalman filter is constructed. We base our study on simulated and real data from the ground network of 8 GPS receivers operating in Goteborg, Sweden. The results demonstrate that at present the limitations of the GPS tomographic technique are errors in the retrieved wet slant delays and their poor geometric distribution.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of GPS Tomography: First Results From A Permanent Local Network

We will draw attention to a new technique for retrieval of water vapor fields, which is based on ... more We will draw attention to a new technique for retrieval of water vapor fields, which is based on the use of a small network of GPS receivers, and is referred to as GPS tomography. A subset of the inverse theory utilizing the integrated values of the field distribution is called tomography. To demonstrate the technique we use a permanent local GPS network consisting of 8 stations and located in the G"{o}teborg area (Swe- den). Its baselines range from a few to 15 km. Tomographic results from this network are derived by applying a tomographic method on the measured slant delay values at each site. The method is implemented in the software package LOTTOS (LOcal Tropospheric Tomographic SOftware developed by Alejandro Flores) and is able to produce a tomographic solution of the water vapor induced refractivity in the tropo- sphere. In tropospheric tomography the slant delay values are obtained by combining the estimated zenith delay values with the horizontal gradients. The geometry using GPS is somewhat restricted compared to the classical tomographic approaches where one can choose the direction of the scanning rays. In the case of GPS tomography, we are limited by the satellite constellation and therefore in certain areas of the field that we want to reconstruct some "information gaps" will be present. In order to reduce these uncertainties, additional vertical and horizontal constraints should be included in the solution. Other ways of increasing the information could be: optimization of tomographic grid used, inclusion of more GPS stations and/or additional independent data from GLONASS, GALILEO (in the future), GPS occultation receivers, radioson- des or scanning pointed water vapor radiometers (WVR). We first present simulations of a tomographic solution based on our particular site distribution, sensitivity analyses of the network, as well as some grid optimization results. Impact of GLONASS data inclusion on the water vapor zenith and gradient estimates is studied by comparisons to a WVR. First comparisons of the tomographic results using real data with results from measurements from radiosondes launched in the vicinity the GPS network are also presented. The achievable time resolution of the obtained refractivity profiles can be from some minutes to hours depending on the data availability and the vertical spatial resolution used, which we set to vary within few hundreds of meters.

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Research paper thumbnail of Site-Dependent Electromagnetic Effects in High-Accuracy Applications of GNSS

Agu Fall Meeting Abstracts, Dec 1, 2008

Global Navigation Satellite Systems, GNSS are used in many applications demanding millimetre-leve... more Global Navigation Satellite Systems, GNSS are used in many applications demanding millimetre-level accuracy in positioning. Such applications include monitoring of crustal movements. The GNSS technique also facilitates estimates of the tropospheric water vapour content, an important parameter in numerical weather predictions and climate research. The accuracy of estimated parameters is however degraded by many error sources. Some of those are related to the satellite system and the ground-based receivers. During 2006 the International GNSS Service, IGS implemented absolute antenna calibration for both satellite antennas and the different antenna types used at the ground-based stations. The use of such calibration values improves the accuracy as antenna type related errors are mitigated. However, unmodeled error sources still remain since a antenna couples electromagnetically with its surrounding environment. The absolute antenna calibrations, to be implemented by the IGS, will however not compensate for site- dependent effects. To further improve the accuracy, the site-dependent effects and their dependency on the direction of the observation need to be identified and removed in the GNSS data analysis. In this presentation the site-dependent error sources have been studied for the stations in the Swedish permanent GNSS network, SWEPOS, as well as some stations in the global IGS network. Strong similarities in terms of site-dependent effects were found. Differences in the site characteristics, caused by multipath and different antenna surroundings imply that an individual calibration of each station may be required needed. We have developed and evaluated two different methods for calibration of site dependent effects.

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Research paper thumbnail of Media calibration system for deep space missions: preliminary design and technical aspects

Bookmarks Related papers MentionsView impact