HR: 08:00h
AN: G21A-01 INVITED     [PDF]
TI: Requirements for Improved Definitions and Realizations of the ITRF Origin and Geocenter Motion
AU: * Ray, J
EM: jimr@ngs.noaa.gov
AF: National Geodetic Survey, 1315 East-West Hwy, Silver Spring, MD 20910 United States
AU: * Ray, J
EM: jimr@ngs.noaa.gov
AF: Bureau International des Poids et Mesures, Pavillon de Breteuil, Sevres, F-92312 France
AU: Petit, G
EM: gpetit@bipm.org
AF: Bureau International des Poids et Mesures, Pavillon de Breteuil, Sevres, F-92312 France
AU: Altamimi, Z
EM: altamimi@ensg.ign.fr
AF: Institut Geographique National, 6-8 Avenue Blaise Pascal, Cite Descartes, Marne-la-Vallee, F-77455 France
AB: The International Terrestrial Reference Frame (ITRF) currently assumes a framework of points rigidly attached to a hypothetical solid Earth surface wherein the points move only due to linear tectonic motions and accurately predictable tidal (periodic) effects. The ITRF origin is specified as coincident with the the geocenter, the center of mass of the entire Earth system, and is realized by long-term dynamical solutions of satellite laser ranging (SLR) data. Within this otherwise secular framework, small relative motions of the geocenter and the ITRF origin due to large-scale mass redistributions within the Earth system can be treated empirically as pure translations if the ITRF retains its rigidity. This approach has been used in analyses of SLR, DORIS, and GPS data to demonstrate "geocenter motions" at the few-mm level, roughly consistent with models for geophysical fluid variations. Effects are most significant at semi-diurnal and diurnal tidal periods, and at seasonal timescales. However, differences among observing techniques and analysis groups imply that important systematic errors remain, and insufficiently robust data exist to accurately quantify the expected geophysical mass effects. These realities complicate efforts to observationally realize a reliable time series of geocenter motions. Difficulties apply at a conceptual level, as well. For instance, the assumption of ITRF rigidity is inconsistent with the actual surface deformations expected due to large-scale mass motions. The International Earth Rotation and Reference Systems Service is considering more accurate definitions and specifications to provide a more consistent framework for the expression of measured ITRF quantities, including satellite orbits and Earth orientation.
DE: 1223 Ocean/Earth/atmosphere interactions (3339)
DE: 1229 Reference systems
DE: 1241 Satellite orbits
DE: 1244 Standards and absolute measurements
DE: 1247 Terrestrial reference systems
SC: Geodesy [G]
MN: 2003 Fall Meeting