HR: 0800h
AN: G41B-0354    [Abstracts]
TI: Impact of thermal expansion of VLBI radio telescopes on the scale of the International Terrestrial Reference Frame
AU: * Collilieux, X
EM: xavier.collilieux@ensg.ign.fr
AF: Institut G‚ographique National - LAREG, 6-8 Avenue Blaise Pascal Champs-Sur-Marne, Marne-La-Vall‚e, 77455 France
AU: Altamimi, Z
EM: altamimi@ensg.ign.fr
AF: Institut G‚ographique National - LAREG, 6-8 Avenue Blaise Pascal Champs-Sur-Marne, Marne-La-Vall‚e, 77455 France
AU: Ray, J
EM: jimr@ngs.noaa.gov
AF: National Geodetic Survey, 1315 East-West Hwy, Silver Spring, MD 20910 United States
AB: Only VLBI and SLR contribute to the definition of the scale of the International Terrestrial Reference Frame (ITRF), due to unresolved systematic effects in the other techniques. The new ITRF version (namely ITRF2004), which will be available before the end of 2005, is based, for the first time, on time series of station positions and Earth Orientation Parameters rather than on global solutions. Analysis of VLBI and SLR submitted times series show significant annual variations in their scales with respect to the ITRF2000. The annual VLBI and SLR scale terms agree reasonably well in phase but the amplitude of the VLBI variation is larger than for SLR. It is now recognized that thermal deformation of VLBI telescope structure affects position estimates at a detectable level. This phenomenon causes variations of the vertical (mostly) position of the VLBI antenna reference points with typical daily and annual signatures, and with a magnitude of a few millimeters. The present study aims to investigate the impact of these VLBI thermal deformations on the reference frame parameters, notably the scale. A simple model of the thermal deformation contribution to VLBI scale will be presented with a special emphasis on annual variations. Comparisons of this model with scale differences between VLBI and SLR derived from available time series reveal a good agreement in annual amplitude and phase so that thermal deformation might be largely responsible for the difference between annual VLBI and SLR scale signals. As a consequence, the use of a thermal deformation model by VLBI analysis centers is strongly advised to decrease the annual signal of VLBI scale changes with respect to ITRF2000.
DE: 1229 Reference systems
DE: 1295 Integrations of techniques
SC: Geodesy [G]
MN: Fall Meeting 2005