HR: 10:50h
AN: G22A-03    [Abstracts]
TI: Is there Utility in Rigorous Combinations of VLBI and GPS EOPs?
AU: Kouba, J
EM: kouba@geod.NRCan.gc.ca
AF: Natural Resources Canada, 458A-615 Booth Street, Ottawa, K1A 0E9 Canada
AU: * Ray, J
EM: jimr@ngs.noaa.gov
AF: National Geodetic Survey, 1315 East-West Hwy, Silver Spring, MD 20910 United States
AU: Altamimi, Z
EM: altamimi@ensg.ign.fr
AF: Institut Geographique National LAREG, 6-8 Avenue Blaise Pascal, Champs-sur-Marne, 77455 France
AB: Combinations of station positions and velocities from independent space geodetic techniques have long been the standard method to realize global terrestrial reference frames. In principle, the particular strengths of one observing method can compensate for weaknesses in others if the combination is properly constructed, suitable weights are found, and accurate colocation ties are available. More recently, the methodology has been extended to combine time series of results at the normal equation level. This allows Earth orientation parameters (EOPs) to be included in a fully consistent way. While the utility of such multi-technique combinations is generally recognized for the reference frame, its benefit for the EOPs is still to be accurately assessed, though it is indispensable for better alignment with the frame. We have studied test combinations of VLBI and GPS time series solutions to assess the effects on combined EOP measurements. One expects any effects to be small, considering that GPS dominates the polar motion estimates due to its relatively dense and uniform global network coverage, high precision, daily sampling, and homogeneity, while VLBI solely observes UT1. Presently, we see no practical method to include the GPS estimates of length-of-day variations due to significant time-varying biases. Nevertheless, there are indications that the stronger reference frame from GPS contributes slightly to improved UT1 results. The situation with polar motion is less clear. The VLBI data contribute only slightly, increasing coherence with geophysical excitations in some spectral bands while decreasing it in others. The effects differ between the X and Y components but are small in both cases. Variations in the combination strategy also affect the assessments at a similar level. Further research is needed to determine an optimal combination strategy that yields the highest quality EOP estimates.
DE: 1200 GEODESY AND GRAVITY
DE: 1223 Ocean/Earth/atmosphere interactions (3339)
DE: 1247 Terrestrial reference systems
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting