in an
IGS/BIPM Pilot Project to Study
Accurate Time and Frequency Comparisons
Using GPS Phase and Code Measurements
The International GPS Service (IGS) and the Bureau International des Poids et Mesures (BIPM) have established a joint Pilot Project for Time and Frequency Comparisons using GPS. The goal of this Pilot Project is to investigate the use of GPS phase and code measurements to improve worldwide availability of accurate time and frequency.
GPS offers the opportunity for highly accurate time and frequency transfer among many remote sites. In their analyses of GPS observations, the IGS Analysis Centers have the potential for determining clock differences with uncertainties well below one nanosecond. These results are comparable to those of the best techniques available. To exploit this potential, however, important technical issues remain to be resolved, which this Pilot Project is investigating.
The Pilot Project is open to all relevant groups, agencies, and individuals. These activities are not intended to limit in any way the freedom of participants to engage in independent research. The objective is to organize and coordinate efforts among groups to achieve the goals of the Project and to share resources, data, and experiences. The Pilot Project is being conducted by a Working Group formed by those responding to this Call for Participation.
It is expected that the goals of the Pilot Project will require activities in a variety of areas, including those listed below. Investigators are invited to participate in one or more areas.
1) Deployment of GPS receivers
In addition to the GPS receivers already installed as part of the IGS global tracking network, other receivers in laboratories having accurate time standards are sought. These should be high-quality geodetic receivers capable of recording and rapidly transmitting dual-frequency code and carrier phase observations. The station configuration and data distribution should conform to IGS standards and appropriate documentation must be filed with the IGS Central Bureau. A log file should be completed and maintained for each IGS station. In addition, due consideration should be given to electronic stability and environmental control. Upgrading of existing tracking stations for better timing performance is also encouraged.
2) GPS data analysis
Strategies for analyzing GPS phase and code observations must be developed, consistent with other IGS products, to allow the routine, accurate characterization of time standards at a large number of independent GPS receiver sites. This work will be done in close cooperation with the IGS Analysis Coordinator. It is expected that regular reports will be issued by participating analysis centers, analogous to those distributed by the IGS for other activities.
3) Analysis of instrumental delays
In order to relate clock estimates derived from GPS data analysis to external timing standards it is necessary to understand the instrumental electronic delays introduced by the associated hardware. Studies are sought to characterize the short-term and long-term sensitivities to environmental changes and to develop calibration methods. Differences for the L1 and L2 frequencies must be considered. Studies of both GPS ground sites as well as the GPS satellites are sought.
4) Time transfer comparisons
Simultaneous, independent time and frequency comparison data are needed to compare with the GPS-derived estimates. Collaborations are sought with groups performing time transfer experiments using a variety of techniques. Close cooperation is expected with the Consultative Committee for Time and Frequency (CCTF) of the Comité International des Poids et Mesures (CIPM).
GPS observational data should be distributed using the IGS hierarchy of data centers and appropriate standards and formats. Analysis reports should be distributed electronically as part of the IGS Reports series. In addition, an e-mail exploder list will be assembled to allow a free exchange of communications among Working Group members and a World Wide Web site will be constructed for the Pilot Project.
The Pilot Project will be conducted by the Working Group formed by this Call for Participation. The operation of the Working Group will be self-directed through consensus of the participants. Subdivision of the Working Group into topical sub-groups may be considered.
The Working Group is co-chaired by:
Dr. Jim Ray (USNO), representing IGS e-mail = jimr@maia.usno.navy.mil Dr. Felicitas Arias, representing BIPM e-mail = farias@bipm.org
It is anticipated that the schedule of activities will be reasonably flexible. However, for planning purposes the following schedule is suggested:
01 Jan. 1998 -- Call for Participation distributed
15 Mar. 1998 -- Responses to Call for Participation due
01 Apr. 1998 -- Establishment of Pilot Project Working Group
01 Jun. 1998 -- Target for publication of first analysis report
Dec. 1998 -- Interim report to IGS Governing Board
Spring 1999 -- Report to Consultative Committee for Time and Frequency
Dec. 1999 -- Report to IGS Governing Board and BIPM
Sep. 2000 -- Workshop
Spring 2001 -- Final report to Consultative Committee for Time and Frequency
Dec. 2001 -- Final report to IGS Governing Board and BIPM
Investigators interested in participating in this Pilot Project are asked to return the following reponse form to Jim Ray at the e-mail address: jimr@maia.usno.navy.mil and to Felicitas Arias at the e-mail address: farias@bipm.org.
Response to CALL FOR PARTICIPATION in an
IGS/BIPM PILOT PROJECT TO STUDY ACCURATE TIME AND FREQUENCY
COMPARISONS USING GPS PHASE AND CODE MEASUREMENTS
Agency or group:
Contact person(s):
E-mail address(es):
Areas of participation:
1) Deployment of GPS receivers: Yes or No
2) GPS data analysis: Yes or No
3) Analysis of instrumental delays: Yes or No
4) Time transfer comparisons: Yes or No
6) other: (please list)
Limitations on participation: (please list any restrictions)
Comments or suggestions:
Please return to jimr@maia.usno.navy.mil and farias@bipm.org.