HR: 09:10h
AN: G21B-05    [Abstracts]
TI: Rate Difference Between VLBI and GPS Reference Frame Scales
AU: * MacMillan, D S
EM: dsm@leo.gsfc.nasa.gov
AF: NVI, Inc./NASA GSFC, Code 926, Greenbelt, MD 20771 United States
AB: For analysis of VLBI data, we apply different reference frame procedures depending on the problem being investigated. One class of solutions is for determination of the secular variation of site positions. Here we estimate the positions and velocities of sites over their entire histories of observations. To place the solution in a particular reference frame, we apply no-net translation and rotation constraint conditions. In comparisons between VLBI and GPS (JPL) site velocities at 22 colocated sites, both given in their own realizations of the ITRF2000 frame, we have found that GPS vertical rates are an average of 1.5 mm/yr (or about 0.2 ppb/yr) greater than the VLBI vertical rates. GPS baseline length rates of change are also on average about 0.2 ppb/yr greater than the corresponding VLBI baseline length rates. We investigate whether this difference can be explained by reference frame and modeling differences between the two techniques. The discrepancy is examined in the context of choosing the appropriate reference frame for studies at specific sites. For example, we recently investigated whether observed geodetic rates at Ny-Alesund, Svalbard in the Arctic can be explained by effects including post-glacial rebound and present-day ice melting, where the discrepancy between the vertical rates from the two techniques is significant compared to these effects. We also compare VLBI velocities with collocated GPS site velocities from several different GPS analysis centers in order to help resolve the source of the apparent scale rate difference.
DE: 1206 Crustal movements--interplate (8155)
DE: 1229 Reference systems
DE: 1247 Terrestrial reference systems
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting