| Date: | 1996-12-31 15:00:00 | |
| Sender: | Jim Ray <[Mailed Jim Ray (NOAA 301-713-2850) <jimr@ray.grdl.noaa.gov>]> | |
| Subject: | [SLR-Mail] No. 39: IERS Geocenter Analysis Campaign | |
| Author: | Jim Ray | |
| Content: | ******************************************************************************** SLR Electronic Mail 1996-12-31 15:00:00 UTC Message No. 39 ******************************************************************************** Author: Jim Ray Subject: IERS Geocenter Analysis Campaign Mailer: Elm [revision: 72.14] ============================================================================== INTERNATIONAL EARTH ROTATION SERVICE (IERS) SERVICE INTERNATIONAL DE LA ROTATION TERRESTRE CALL FOR PARTICIPATION IN AN IERS ANALYSIS CAMPAIGN TO INVESTIGATE MOTIONS OF THE GEOCENTER ============================================================================== Background ---------- Analyses of satellite tracking data have provided persuasive evidence that the coordinate frame formed by the tracking stations attached to the Earth´s crust moves detectably relative to the Earth´s center of mass. This translational motion, when viewed from a crust-fixed frame, is known as ”geocenter motion” and is caused by the mass movement of planetary fluids, primarily the atmosphere and oceans. It apparently has a total magnitude of up to a few centimeters and consists of two components. The tidal variations have mostly diurnal and semi-diurnal periods and are predominantly caused by oceanic motions; the non-tidal geocentric motions are thought to be due primarily to atmospheric mass motions, ocean circulation, and surface water storage. The IERS is charged with maintaining a geocentric terrestrial reference frame, including the effect of the atmospheric and oceanic masses. Currently the International Terrestrial Reference Frame (ITRF) gives coordinates of stations relative to the position of the Earth´s center of mass averaged over about 20 years of SLR observations. In order to provide improved accuracy for instantaneous geocentric coordinates, it has been proposed that the IERS collect and distribute tabulated results for geocenter motions, analogous to the Earth orientation service already provided by the IERS. To better understand this phenomenon and the capabilities of the various satellite-tracking techniques, the IERS Working Group on the ITRF Datum is organizing this Analysis Campaign to collect appropriate products from interested space geodetic data analysis centers and geophysical data analysis centers, and to compare the results. While it is likely that the results of this Campaign will strongly influence any future IERS activity to regularly monitor geocenter motions, participation in this Campaign does not obligate a participant to contribute to any future operational activities. This Campaign does not request the collection of any new observational data not already being collected for other purposes. For further information on the ITRF and the IERS Working Group on the ITRF Datum, please refer to the www site http://schubert.ign.fr:8000/CIAG/WITRF/index.WITRF.html. Areas of participation ---------------------- This Call for Participation seeks collaborators in the following areas. Investigators are invited to participate in one or more areas. In order to facilitate intercomparison of results, guidelines have been developed for certain common elements. The guidelines document is available anonymously at ftp://ray.grdl.noaa.gov/pub/gc-iers.guide. 1) Analysis of satellite-tracking data Observations of the Earth´s center of mass are inferred by analyzing the dynamics of satellite orbits. To date, the most thorough studies of geocenter motion have been made by researchers at the Center for Space Research using observations of LAGEOS, and historically these solutions have been used to realize the origin of the ITRF. Recently, GPS and DORIS have demonstrated similar sensitivities for detecting geocenter motions, although different time resolutions probably apply. Satellite analysis results are sought from all techniques (not only SLR, GPS, and DORIS used by the IERS) to address either or both of the following types of geocenter motion: 1.a) Tidal geocenter variations 1.b) Non-tidal geocenter variations For the study of non-tidal geocenter motions, it is planned that the comparison campaign will cover about 2.5 years of observations with sampling intervals of 1 week or longer. Data products to be compared will include time series of sets of site coordinates (using the SINEX format). 2) Analysis of atmospheric, oceanic, and/or other geophysical data In order to investigate the relationship between observed geocenter motions and the likely sources of geophysical excitation, analogous products are sought from analyses of atmospheric, oceanic, and/or other fluid mass movements: 2.a) Tidal oceanic geocenter variations 2.b) Non-tidal atmospheric geocenter variations 2.c) Non-tidal oceanic geocenter variations 2.d) Effects of other fluid motions on the geocenter Calculations of the integrated effects on the geocenter are sought for: tidal oceanic variations, non-tidal atmospheric mass motions, non-tidal oceanic currents, and/or any other geophysically significant fluid motions. For the study of non-tidal geocenter motions, the comparison campaign will correspond to the same 2.5 year period as in 1.b). 3) Comparison of analysis products The analysis products from 1) and 2) above will be compared and analyzed in parallel by several centers. Publication of results ---------------------- Splinter meetings will probably be organized in conjunction with the EGS XXII General Assembly in Vienna (21-25 Apr. 1997) and/or the Spring ´97 AGU Meeting in Baltimore (27-30 May 1997) to discuss the status of activities among the Campaign participants. It is expected that a special session will be convened at the Fall ´97 AGU Meeting in San Francisco (Dec. 1997) to present the final results of the Campaign. Reports and analyses from all participants in this Campaign will be collected and published as an IERS Technical Note. If warranted, a group journal paper(s) may also be recommended to summarize the significant results that emerge. Participants in this Campaign will not be under any obligation to contribute to any such journal papers. Schedule -------- It is anticipated that the schedule of activities will be reasonably flexible. However, for planning purposes the following schedule is suggested: 01 Jan. 1997 -- Call for Participation released 15 Feb. 1997 -- responses from interested participants due 21 Apr. 1997 -- start of EGS XXII General Assembly, Vienna 27 May 1997 -- start of Spring ´97 AGU Meeting, Baltimore 01 Jul. 1997 -- submittal of analysis products from satellite, atmospheric, and oceanic data 31 Oct. 1997 -- submittal of first round comparison results 08 Dec. 1997 -- start of Fall ´97 AGU Meeting, San Francisco later -- review of results by IERS Directing Board Response form ------------- Investigators who are interested in participating in this Analysis Campaign are requested to return the following reponse form by 15 Feb. 1997 to Jim Ray chairman, IERS Working Group on the ITRF Datum e-mail: jimr@ray.grdl.noaa.gov All participants will be included in an e-mail exploder list at geoc@ray.grdl.noaa.gov. The guidelines document for the Analysis Campaign is available anonymously at ftp://ray.grdl.noaa.gov/pub/gc-iers.guide. ------------------------------------------------------------------------------ Response to CALL FOR PARTICIPATION in IERS ANALYSIS CAMPAIGN to INVESTIGATE MOTIONS OF THE GEOCENTER Agency or group: Contact person(s): E-mail address(es): Areas of participation: 1) Analysis of satellite-tracking data: Y or N (if Y, give technique) a) Tidal geocenter variations: Y or N b) Non-tidal geocenter variations: Y or N 2) Analysis of atmospheric and/or oceanic effects on geocenter: a) Tidal oceanic: Y or N b) Non-tidal atmospheric: Y or N c) Non-tidal oceanic: Y or N d) Effects of other fluid motions: Y or N 3) Comparison of analysis products: Y or N Limitations on participation: (please list any restrictions) Comments or suggestions: Please return to jimr@ray.grdl.noaa.gov, preferably by 15 Feb. 1997 ============================================================================== [Mailed From: Jim Ray (NOAA 301-713-2850) ******************************************************************************** |