Definition of a Terrestrial Reference Frame using IRIS VLBI Observations; Approaching Millimeter Accuracy

Abstract

The data now available from space-based geodetic observing techniques, especially Very- Long-Baseline Interferometry and Satellite Laser ranging, presently allow us to define a terrestrial reference frame with an accuracy of better than two centimeters. Improvements to the observing systems over the next few years may allow accuracies approaching a few millimeters. These unprecedented accuracy levels raise a number of interesting technical and scientific questions concerning the accuracy of the Earth models used to reduce the data. For example, observations of the changes in the lengths of baselines from North America to Europe show 25 to 30% discrepancies from the values given by the Minster- Jordan AMO-2 plate motion model, which is now uniformly adopted for processing the new data. Also, vertical crustal motions expected from glacial rebound not presently included in the data reduction can exceed 1 cm per year at some sites. Existing VLBI observing networks lack the global coverage necessary to realize the potential of the present accuracy levels. In the next few years much effort will need to be directed toward establishing observatories in under-represented portions of the globe, especially the southern hemisphere and the central Asia-Indian ocean regions.