Measurements of the Doppler-velocity fluctuations indicated by the radio signals from the Vega ba... more Measurements of the Doppler-velocity fluctuations indicated by the radio signals from the Vega balloons testify to strong turbulence in the nightside as well as the dayside Venus cloud layer. Wind speeds vary by up to 2 m/sec on time scales of 30-100 sec.
Proceedings of the International Astronomical Union, 2012
The IERS Conventions (2010) provides the international standard for models for use in the generat... more The IERS Conventions (2010) provides the international standard for models for use in the generation of celestial reference systems (CRS), terrestrial reference systems (TRS), and the Earth orientation parameters (EOPs) that relate the associated frames. Significant improvements over the previous IERS Conventions (2003) are outlined, and an overview of the latest adopted models and standards is shown. Finally, future plans for the Conventions are provided.
Proceedings of the International Astronomical Union, 2009
In the last years, a fully general relativistic definition of reference systems and of their appl... more In the last years, a fully general relativistic definition of reference systems and of their application to astronomy and geodesy has been passed into Resolutions of the scientific unions, following work of several working groups and of the community at large. In this community, the role of the International Earth Rotation and Reference systems Service (IERS) is to generate the terrestrial and celestial reference systems and the transformation between them, and the IERS Conventions provide the set of models and procedures used in the generation of IERS products. It is therefore essential that the IAU framework for relativity is introduced in the IERS Conventions, and that this is done consistently and completely throughout the document. The paper reviews relativistic aspects in the IERS Conventions and presents recent and on-going work aiming at providing a complete and consistent presentation for a new reference edition of the IERS Conventions, expected to appear in the next year.
Since early eighties, the introduction of new methods for distant time transfer has led to a majo... more Since early eighties, the introduction of new methods for distant time transfer has led to a major improvement in the precision, accuracy, and coverage of world-wide time metrology. All of these methods are based on the use of satellites. Communication between ground stations and satellites is effected through microwave or optical signals according to a one-way or two-way mode.
International Atomic Time TAI gets its stability from some 400 atomic clocks worldwide that gener... more International Atomic Time TAI gets its stability from some 400 atomic clocks worldwide that generate the free atomic scale EA L and its accuracy from a small number of primary frequency standards (PFS) which frequency measurements are used to steer the EAL frequency. Because TAI is computed in "real - time" (every month) and has operational constraints, it is not optimal and the BIPM computes in deferred time another time scale TT(BIPM), which is based on a weighted average of the evaluations of TAI frequency by the PFS. We show that a point has been reached where the stability of atomic time scales, the accuracy of primary frequency standards, and the capabilities of frequency transfer are approximately at a similar level, in the low 10 - 16 in relative frequency. The goal is now to reach and surpass 1x10 - 16 and the three fields are in various stages of advancement towards this aim. We review the stability and accuracy recently achieved by frequency standards, focusing ...
With the present level of accuracy it may be necessary to use space borne atomic clocks to direct... more With the present level of accuracy it may be necessary to use space borne atomic clocks to directly generate TCG, and to start addressing the limitations in the coordinate time transformations.
The BIPM/IAU Joint Committee on relativity for spacetime reference systems and metrology (JCR) ha... more The BIPM/IAU Joint Committee on relativity for spacetime reference systems and metrology (JCR) has worked in collaboration with the IAU Working Group on relativity for celestial mechanics and astrometry (RCMA) on the problems of astronomical relativistic space-time reference frames and the RCMA has proposed to the IAU a consistent framework for defining the barycentric and geocentric celestial reference systems at the first post-Newtonian level. Because new clock technology and space missions will necessitate the application of this framework for time and frequency measurements in the solar system, practical resolutions are proposed by the JCR to the IAU to allow a consistent treatment of these measurements. The paper outlines the conclusions of the work which resulted in the proposed IAU resolutions.
We discuss the use of some new time transfer techniques for computing TAI time links. Precise poi... more We discuss the use of some new time transfer techniques for computing TAI time links. Precise point positioning (PPP) uses GPS dual frequency carrier phase and code measurements to compute the link between a local clock and a reference time scale with the precision of the carrier phase and the accuracy of the code. The time link between any two stations can then be computed by a simple difference. We show that this technique is well adapted and has better short-term stability than other techniques used in TAI. We present a method of combining PPP and two-way time transfer that takes advantage of the qualities of each technique, and shows that it would bring significant improvement to TAI links.
Proceedings of the International Astronomical Union, 2007
Most of the Commission's three 90-minute time slots at the General Assembly were devoted to a... more Most of the Commission's three 90-minute time slots at the General Assembly were devoted to a series of 20 and 50 minute presentations, informally termed “Time and Astronomy”. The first part of the meeting was dedicated to time and general relativity. The second part of the session was dedicated to pulsar timing.
Proceedings of the International Astronomical Union, 2010
Dr R. N. Manchester and Dr M. Hosokawa have been elected as, respectively, the new President and ... more Dr R. N. Manchester and Dr M. Hosokawa have been elected as, respectively, the new President and Vice-President of the Commission for the next term, 2009-2012. Concerning the Organizing Committee (OC) Members, we welcome as new members: Felicitas Aris (BIPM, France), Philip Tuckey (LNE-SYRTE, France), Vladimir Zharov (MSU, Russia), and Shougang Zhang (NTSC, China) and we acknowledge the outgoing members: Demetrios Matsakis, Gerard Petit, Mizuhiko Hosokawa, Sigfrid Leschiutta and Zao-Cheng Zhai. P. Defraigne remains on the OC as immediate Past-President.
EFTF-2010 24th European Frequency and Time Forum, 2010
This paper reviews the requirements on GNSS receiver setups for precise time and frequency transf... more This paper reviews the requirements on GNSS receiver setups for precise time and frequency transfer; these concern the receiver itself, the GNSS measurements, the antenna and cables used in the full setup. Concerning the receiver, we show that for a high level scientific use of a GNSS receiver within the frame of timing applications, it is essential that certain time delay related parameters be described in detail by the manufacturer.
2011 Joint Conference of the IEEE International Frequency Control and the European Frequency and Time Forum (FCS) Proceedings, 2011
Measurements from Global Navigation Satellite Systems (GNSS) have been used since the eighties to... more Measurements from Global Navigation Satellite Systems (GNSS) have been used since the eighties to perform precise and accurate Time and Frequency Transfer (TFT). Two main approaches are used presently: the Common View or All in View based on the Common GPS GLONASS Time Transfer Standard (CGGTTS) and the Precise Point Positioning (PPP). Concerning the CGGTTS approach, in order to allow the use of GLONASS data from geodetictype receivers providing only raw data in RINEX format, the R2CGGTTS software developed initially for GPS at the Royal Observatory of Belgium (ROB) was updated. The GLONASS navigation files are used for the determination of satellite clocks and positions, and the computation procedure to get the CGGTTS data from the pseudorange measurements is applied similarly as for the GPS satellites. In parallel, we also upgraded the PPP software Atomium developed at the ROB to allow the use of the Russian GLONASS constellation. The clock solution is then obtained through the analysis of dual-frequency carrier-phase and pseudorange measurements. This study combines GPS and GLONASS observations in PPP in order to determine the added value of the GLONASS data in geodetic time transfer.
We review the stability and accuracy achieved by the reference atomic time scales TAI and TT(BIPM... more We review the stability and accuracy achieved by the reference atomic time scales TAI and TT(BIPM). We show that they presently are at the level of a few 10 −16 in relative value, based on the performance of primary standards, of the ensemble time scale and of the time transfer techniques. We consider how the 1 × 10 −16 value could be reached or superseded and which are the present limitations to attain this goal.
It is well known that two timescales, one based on the Earth's rotation and generically called Un... more It is well known that two timescales, one based on the Earth's rotation and generically called Universal Time, and the other based on the Earth's orbital motion and generically called Ephemeris Time, diverge. The divergence is explained mostly by a secular slowing down of the Earth's rotation due to tidal braking. This paper investigates the question whether relativistic time dilation plays any role in this divergence, as it has sometimes been proposed. After a detailed analysis from the point of view of general relativity, we demonstrate that relativistic time dilation does not influence the divergence in question. We conclude that there is no reason to refute the present understanding of the secular variation of Earth's rotation.
Concerning the problem of astronomical relativistic space-time reference frames suggestions for I... more Concerning the problem of astronomical relativistic space-time reference frames suggestions for IAU-recommendations are given. New clock technology and space missions will necessitate the application of the framework for time and frequency measurements in the solar system. Practical recommendations are suggested to allow a consistent treatment of these measurements.
AbstractReviewing calibration results over the history since early 1980's among several lab... more AbstractReviewing calibration results over the history since early 1980's among several labs shows very mixed results. The best stabilities of GPS receivers, as given by calibrations, are of the order of a few nanoseconds or better over a year, though many results are quite ...
The Bureau International des Poids et Mesures (BIPM) is in charge of producing International Atom... more The Bureau International des Poids et Mesures (BIPM) is in charge of producing International Atomic Time TAI. In this aim, it uses clock data from more than 60 laboratories spread worldwide. For two decades, GPS has been an essential tool to link these clocks, and products from the International GNSS Service (IGS) have been used to improve the quality of
Measurements of the Doppler-velocity fluctuations indicated by the radio signals from the Vega ba... more Measurements of the Doppler-velocity fluctuations indicated by the radio signals from the Vega balloons testify to strong turbulence in the nightside as well as the dayside Venus cloud layer. Wind speeds vary by up to 2 m/sec on time scales of 30-100 sec.
Proceedings of the International Astronomical Union, 2012
The IERS Conventions (2010) provides the international standard for models for use in the generat... more The IERS Conventions (2010) provides the international standard for models for use in the generation of celestial reference systems (CRS), terrestrial reference systems (TRS), and the Earth orientation parameters (EOPs) that relate the associated frames. Significant improvements over the previous IERS Conventions (2003) are outlined, and an overview of the latest adopted models and standards is shown. Finally, future plans for the Conventions are provided.
Proceedings of the International Astronomical Union, 2009
In the last years, a fully general relativistic definition of reference systems and of their appl... more In the last years, a fully general relativistic definition of reference systems and of their application to astronomy and geodesy has been passed into Resolutions of the scientific unions, following work of several working groups and of the community at large. In this community, the role of the International Earth Rotation and Reference systems Service (IERS) is to generate the terrestrial and celestial reference systems and the transformation between them, and the IERS Conventions provide the set of models and procedures used in the generation of IERS products. It is therefore essential that the IAU framework for relativity is introduced in the IERS Conventions, and that this is done consistently and completely throughout the document. The paper reviews relativistic aspects in the IERS Conventions and presents recent and on-going work aiming at providing a complete and consistent presentation for a new reference edition of the IERS Conventions, expected to appear in the next year.
Since early eighties, the introduction of new methods for distant time transfer has led to a majo... more Since early eighties, the introduction of new methods for distant time transfer has led to a major improvement in the precision, accuracy, and coverage of world-wide time metrology. All of these methods are based on the use of satellites. Communication between ground stations and satellites is effected through microwave or optical signals according to a one-way or two-way mode.
International Atomic Time TAI gets its stability from some 400 atomic clocks worldwide that gener... more International Atomic Time TAI gets its stability from some 400 atomic clocks worldwide that generate the free atomic scale EA L and its accuracy from a small number of primary frequency standards (PFS) which frequency measurements are used to steer the EAL frequency. Because TAI is computed in "real - time" (every month) and has operational constraints, it is not optimal and the BIPM computes in deferred time another time scale TT(BIPM), which is based on a weighted average of the evaluations of TAI frequency by the PFS. We show that a point has been reached where the stability of atomic time scales, the accuracy of primary frequency standards, and the capabilities of frequency transfer are approximately at a similar level, in the low 10 - 16 in relative frequency. The goal is now to reach and surpass 1x10 - 16 and the three fields are in various stages of advancement towards this aim. We review the stability and accuracy recently achieved by frequency standards, focusing ...
With the present level of accuracy it may be necessary to use space borne atomic clocks to direct... more With the present level of accuracy it may be necessary to use space borne atomic clocks to directly generate TCG, and to start addressing the limitations in the coordinate time transformations.
The BIPM/IAU Joint Committee on relativity for spacetime reference systems and metrology (JCR) ha... more The BIPM/IAU Joint Committee on relativity for spacetime reference systems and metrology (JCR) has worked in collaboration with the IAU Working Group on relativity for celestial mechanics and astrometry (RCMA) on the problems of astronomical relativistic space-time reference frames and the RCMA has proposed to the IAU a consistent framework for defining the barycentric and geocentric celestial reference systems at the first post-Newtonian level. Because new clock technology and space missions will necessitate the application of this framework for time and frequency measurements in the solar system, practical resolutions are proposed by the JCR to the IAU to allow a consistent treatment of these measurements. The paper outlines the conclusions of the work which resulted in the proposed IAU resolutions.
We discuss the use of some new time transfer techniques for computing TAI time links. Precise poi... more We discuss the use of some new time transfer techniques for computing TAI time links. Precise point positioning (PPP) uses GPS dual frequency carrier phase and code measurements to compute the link between a local clock and a reference time scale with the precision of the carrier phase and the accuracy of the code. The time link between any two stations can then be computed by a simple difference. We show that this technique is well adapted and has better short-term stability than other techniques used in TAI. We present a method of combining PPP and two-way time transfer that takes advantage of the qualities of each technique, and shows that it would bring significant improvement to TAI links.
Proceedings of the International Astronomical Union, 2007
Most of the Commission's three 90-minute time slots at the General Assembly were devoted to a... more Most of the Commission's three 90-minute time slots at the General Assembly were devoted to a series of 20 and 50 minute presentations, informally termed “Time and Astronomy”. The first part of the meeting was dedicated to time and general relativity. The second part of the session was dedicated to pulsar timing.
Proceedings of the International Astronomical Union, 2010
Dr R. N. Manchester and Dr M. Hosokawa have been elected as, respectively, the new President and ... more Dr R. N. Manchester and Dr M. Hosokawa have been elected as, respectively, the new President and Vice-President of the Commission for the next term, 2009-2012. Concerning the Organizing Committee (OC) Members, we welcome as new members: Felicitas Aris (BIPM, France), Philip Tuckey (LNE-SYRTE, France), Vladimir Zharov (MSU, Russia), and Shougang Zhang (NTSC, China) and we acknowledge the outgoing members: Demetrios Matsakis, Gerard Petit, Mizuhiko Hosokawa, Sigfrid Leschiutta and Zao-Cheng Zhai. P. Defraigne remains on the OC as immediate Past-President.
EFTF-2010 24th European Frequency and Time Forum, 2010
This paper reviews the requirements on GNSS receiver setups for precise time and frequency transf... more This paper reviews the requirements on GNSS receiver setups for precise time and frequency transfer; these concern the receiver itself, the GNSS measurements, the antenna and cables used in the full setup. Concerning the receiver, we show that for a high level scientific use of a GNSS receiver within the frame of timing applications, it is essential that certain time delay related parameters be described in detail by the manufacturer.
2011 Joint Conference of the IEEE International Frequency Control and the European Frequency and Time Forum (FCS) Proceedings, 2011
Measurements from Global Navigation Satellite Systems (GNSS) have been used since the eighties to... more Measurements from Global Navigation Satellite Systems (GNSS) have been used since the eighties to perform precise and accurate Time and Frequency Transfer (TFT). Two main approaches are used presently: the Common View or All in View based on the Common GPS GLONASS Time Transfer Standard (CGGTTS) and the Precise Point Positioning (PPP). Concerning the CGGTTS approach, in order to allow the use of GLONASS data from geodetictype receivers providing only raw data in RINEX format, the R2CGGTTS software developed initially for GPS at the Royal Observatory of Belgium (ROB) was updated. The GLONASS navigation files are used for the determination of satellite clocks and positions, and the computation procedure to get the CGGTTS data from the pseudorange measurements is applied similarly as for the GPS satellites. In parallel, we also upgraded the PPP software Atomium developed at the ROB to allow the use of the Russian GLONASS constellation. The clock solution is then obtained through the analysis of dual-frequency carrier-phase and pseudorange measurements. This study combines GPS and GLONASS observations in PPP in order to determine the added value of the GLONASS data in geodetic time transfer.
We review the stability and accuracy achieved by the reference atomic time scales TAI and TT(BIPM... more We review the stability and accuracy achieved by the reference atomic time scales TAI and TT(BIPM). We show that they presently are at the level of a few 10 −16 in relative value, based on the performance of primary standards, of the ensemble time scale and of the time transfer techniques. We consider how the 1 × 10 −16 value could be reached or superseded and which are the present limitations to attain this goal.
It is well known that two timescales, one based on the Earth's rotation and generically called Un... more It is well known that two timescales, one based on the Earth's rotation and generically called Universal Time, and the other based on the Earth's orbital motion and generically called Ephemeris Time, diverge. The divergence is explained mostly by a secular slowing down of the Earth's rotation due to tidal braking. This paper investigates the question whether relativistic time dilation plays any role in this divergence, as it has sometimes been proposed. After a detailed analysis from the point of view of general relativity, we demonstrate that relativistic time dilation does not influence the divergence in question. We conclude that there is no reason to refute the present understanding of the secular variation of Earth's rotation.
Concerning the problem of astronomical relativistic space-time reference frames suggestions for I... more Concerning the problem of astronomical relativistic space-time reference frames suggestions for IAU-recommendations are given. New clock technology and space missions will necessitate the application of the framework for time and frequency measurements in the solar system. Practical recommendations are suggested to allow a consistent treatment of these measurements.
AbstractReviewing calibration results over the history since early 1980's among several lab... more AbstractReviewing calibration results over the history since early 1980's among several labs shows very mixed results. The best stabilities of GPS receivers, as given by calibrations, are of the order of a few nanoseconds or better over a year, though many results are quite ...
The Bureau International des Poids et Mesures (BIPM) is in charge of producing International Atom... more The Bureau International des Poids et Mesures (BIPM) is in charge of producing International Atomic Time TAI. In this aim, it uses clock data from more than 60 laboratories spread worldwide. For two decades, GPS has been an essential tool to link these clocks, and products from the International GNSS Service (IGS) have been used to improve the quality of
Uploads
Papers by Gerard Petit