HR: 16:45h
AN: G24A-04    [Abstracts]
TI: The Importance of Data Equalization for Reducing 'Repeatable' Errors in High-Rate GPS Positions
AU: * Bilich, A
EM: andria.bilich@noaa.gov
AF: National Geodetic Survey, 325 Broadway St. E/GC2, Boulder, CO 80305, United States
AU: Larson, K M
EM: kristinem.larson@gmail.com
AF: Dept. of Aerospace Engineering Sciences University of Colorado, UCB 429, Boulder, CO 80309, United States
AB: When GPS position solutions are computed stochastically, positioning error that would normally be distributed to the solution residuals instead appears in the position estimates. These errors are often several centimeters in magnitude and can easily disguise any geophysical signal, consequently limiting the applicability of raw high-rate GPS positions to geophysical monitoring. Therefore, these position errors must be mitigated for proper integration of high-rate GPS and real-time seismic data. A good deal of recent high-rate GPS research has centered on mitigating high-rate positioning error at the post-processing analysis stage, i.e. removing errors from position timeseries. Many of these techniques (sidereal filtering, modified sidereal filtering, aspect repeat time adjustment) compute positions on one or more days to develop an error profile, align this error profile with a day of interest, and subtract the error profile. The development of these high-rate error reduction techniques has concentrated on determining the perfect time shift to align the error profile with the day of interest. However, proper determination of repeat period is negated if identical data sources are not used in the least squares adjustment - for the satellite-antenna geometry to repeat between two different solutions, the same satellites must be used to compute those solutions and the same number of biases must be resolved. Therefore, for position errors to be truly repeatable, the same satellites and biases must be used in comparable solutions. This paper addresses data equalization, the process by which GPS data on two separate days are brought into spatial alignment and forced to be truly repeatable. We discuss methods for equalizing data before solving for position, and provide examples of data equalization and its effects on error reduction in high-rate GPS positions. Additional data equalization complications are discussed, including equalizing by data quality and accounting for automated data editing algorithms.
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1241 Satellite geodesy: technical issues (6994, 7969)
DE: 1294 Instruments and techniques
DE: 7200 SEISMOLOGY
SC: Geodesy [G]
MN: 2007 Fall Meeting