HR: 09:00h
AN: G31A-05 INVITED     [Abstracts]
TI: The Impact of Source Structure on VLBI Measurements
AU: * Charlot, P
EM: charlot@obs.u-bordeaux1.fr
AF: Observatoire de Bordeaux, BP 89, Floirac, 33270 France
AB: The current limitation of vlbi data analysis is caused predominantly by troposphere and instrumental errors, but also at some level by the extended brightness distribution of the observed radio sources, which are only imperfect fiducial points in the sky at the milliarcsecond scale. Such radio structures give rise to ``structural'' effects in the VLBI measurements, which vary with the length and orientation of the VLBI baselines relative to the source brightness distribution, causing extra ``noise'' for the more extended sources. Temporal evolution of these structures may also result in apparent source position shifts over time when combining observations at several epochs. While these effects have a direct impact on the celestial frame, they also affect at some level Earth rotation and geodetic measurements. This paper will discuss the magnitude of these effects for the sources that are part the International Celestial Reference Frame, especially for those that are routinely used in Earth rotation measurements. It will also review the progress made so far in reducing such errors by including models of source structure in the VLBI data analysis process.
DE: 1229 Reference systems
SC: Geodesy [G]
MN: Fall Meeting 2005