From: Pascal Willis Date: 14 Apr 1999 18:57:16 Subject: [IGEXMail-0290] message from IGEX-98 Steering Committee (plans for the future) ****************************************************************************** IGEX Electronic Mail 14-Apr-1999 18:57:16 Message No 0290 ****************************************************************************** Author: Pascal Willis Subject: message from IGEX-98 Steering Committee (plans for the future) Dear contributors to the IGEX-98 experiment, dear colleagues, The official end of the extended IGEX-98 campaign is approaching rapidly. IGEX-98 was a success beyond expectation, and there is a growing and important scientific user community, in particular in the field time and frequency transfer, urging us to continue with the IGEX-like activities. -------------------------------------------------------------------------- THIS WHY THE IGEX-98 STEERING COMMITTEE REQUESTS YOU TO CONTINUE WITH YOUR IGEX-98 ACTIVITIES ON A BEST EFFORT BASIS AT LEAST UNTIL THE 1999 IGEX WORKSHOP ON SEPTEMBER 13-14 IN NASHVILLE U.S.A., WHERE A CONCRETE PROPOSAL FOR A MORE PERMANENT CONTINUATION OF THE IGEX-98 WILL BE PRESENTED BY THE IGEX STEERING COMMITTEE. -------------------------------------------------------------------------- Before commenting this request, please allow us to express our sincere thanks to all individuals and all institutions, who/which made the IGEX-98 a great success. As a matter of fact, the IGEX-98 campaign has exceeded its initial goals and also its original duration: It is now possible to obtain precise GLONASS orbits from four different analysis groups working with three different software packages using data from the global IGEX-98 GPS/GLONASS tracking network. Several people and institutions already have expressed their willingness to continue their IGEX-98 commitments (for data acquisition, data archiving and data analysis). Other groups have expressed their vital interest in a continuation of the IGEX activities, in particular in the uninterrupted availability of precise GLONASS orbits referring to the IGS realization of the ITRF. As a matter of fact, the IGEX steering committee recently received a letter from Dr. Quinn, Head of Bureau International des Poids et Mesures, expressing the timing community's greatest interest in continuing to receive precise GLONASS orbits (letter attached to this e-mail). There are thus strong arguments to continue the IGEX-98 activities after April 17, 1999 on a more permanent, currently a "best effort" basis. We request you in particular to - continue GLONASS/GPS data acquisition for all dual-frequency GPS/GLONASS instruments - continue SLR tracking of GLONASS satellites (on a reduced scale to be established at the next ILRS Governing Board Meeting) - continue archiving GPS/GLONASS data - continue GLONASS precise orbit computations - complete the scientific investigations you want to present at the IGEX-Workshop in September Regarding single-frequency data collection we propose to apply the following policy: - The current number and distribution of dual-frequency receivers allows for a precise orbit computation without the inclusion of single-frequency data. The single-frequency data set collected during the official IGEX-98 campaign is probably sufficient for all special investigations one might have in mind. - Proposal: Single frequency data is considered useful for validation purposes and for special studies. If there are, however, budgetary or other reasons for a station to discontinue single-frequency operation, this would be acceptable and of no harm at the present stage of the IGEX-experiment. As stated above, the IGEX-98 steering committee considers it appropriate to move from the campaign-type to a more permanent organization. It will take some time, however, to achieve such a goal. Also, such an organization should involve more than just the IGEX steering committee. We believe that it would be most appropriate that a proposal for a more permanent IGEX-continuation should be presented by the IGEX steering committee at the IGEX-Workshop of September in Nashville, where the proposal can be discussed and accepted as a resolution. Such a proposal must be based on your input. We therefore propose the following procedure: - The IGEX steering committee sends out end of April a questionnaire concerning the continuation of the IGEX-98. - IGEX Steering Committee informs the IGS Governing Board on the June 7, 1999 IGS Governing Board Meeting - Proposal for a future IGEX organization prepared by the IGEX steering committee in June/July - Proposal finalized at the IGEX Steering Committee meeting in July (at the IUGG meeting in Birmingham). - Proposal distributed through IGEXMail and IGSMail in August. - Reviewed proposal should be discussed, modified, and adopted as a resolution at the IGEX Workshop in Nashville - IGEX steering committee presents the proposal to the next IGS Governing Board Meeting for approval. We would like to thank you very much in advance for your collaboration. On behalf of the IGEX-98 steering committee Pascal Willis, Chair IGEX-98 =========================================================================== Attachment: Letter by Dr. T.J. Quinn, Director of BIPM =========================================================================== Dear Colleagues, The International GLONASS Experiment (IGEX-98), which has been in progress for about six months, has been well received by the international time metrology community, as the results of this experiment contribute greatly to the research on the best use of the GLONASS constellation for international time transfer. The international time scales - International Atomic Time (TAI) and Coordinated Universal Time (UTC) - are based on data from some 220 atomic clocks located in about 50 time laboratories around the world. Today, the sole method of comparing these clocks to provide data for TAI is the GPS C/A-code common-view technique. The performance of this technique barely covers present needs, and will be not sufficient in the near future to compare the new generation of clocks. This is why the time metrology community is engaged in a number of studies of new time transfer techniques, among which is the use of GLONASS or combined GPS and GLONASS systems. The first tests of the GLONASS precise code time transfer show a significant improvement in performance. Also the availability of GLONASS precise code on two frequencies allows measurements of the ionosphere. In order to take full advantage of GLONASS capabilities for intercontinental time transfer, however, the use of post-processed precise ephemerides is necessary, as it is for GPS. An uncertainty of about 2 ns or better is expected for intercontinental GLONASS time transfer when using precise ephemerides, and only about 10 ns when using broadcast ephemerides. The large participation and excellent results of the IGEX-98 campaign raise the question of transforming this experiment into a permanent service. The Bureau International des Poids et Mesures (BIPM) strongly supports the creation of such a permanent service. The BIPM is already routinely using GPS precise ephemerides produced by IGS. Permanently available GLONASS precise ephemerides would greatly contribute to the diversification of time transfer methods used for the construction of TAI. I congratulate you on the excellent manner in which the IGEX-98 experiment has been conducted and wish you every success in the future. Yours sincerely T. J. QUINN To IGEX-98 Steering Committee: Pascal Willis, - IGN, Chair Gerhard Beutler - AIUB Werner Gurtner - AIUB Ruth Neilan - JPL Guenther Hein - UbM Jim Slater - NIMA ---------------------------------------------------------------------- Pascal Willis ---------------------------------------------------------------------- Institut Geographique National ENSG/LAREG Phone: 33-(0)1-6415-3254 6-8 Avenue Blaise Pascal FAX: 33-(0)1-6415-3253 Cite Descartes, Champs-sur-Marne Email: pascal.willis@ensg.ign.fr 77455 Marne-la-Vallee, France WWW: http://lareg.ensg.ign.fr ----------------------------------------------------------------------