HR: 16:30h
AN: G24A-03 INVITED    [Abstracts]
TI: Accuracy assessment of high-rate GPS measurements for seismology
AU: * Elosegui, P
EM: pelosegui@ice.csic.es
AF: Institute for Space Sciences, CSIC/IEEC, Barcelona, 08034, Spain
AU: Davis, J L
EM: jdavis@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, United States
AU: Ekström, G
EM: ekstrom@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, United States
AB: Analysis of GPS measurements with a controlled laboratory system, built to simulate the ground motions caused by tectonic earthquakes and other transient geophysical signals such as glacial earthquakes, enables us to assess the technique of high-rate GPS. The root-mean-square (rms) position error of this system when undergoing realistic simulated seismic motions is 0.05~mm, with maximum position errors of 0.1~mm, thus providing "ground truth" GPS displacements. We have acquired an extensive set of high-rate GPS measurements while inducing seismic motions on a GPS antenna mounted on this system with a temporal spectrum similar to real seismic events. We found that, for a particular 15-min-long test event, the rms error of the 1-Hz GPS position estimates was 2.5~mm, with maximum position errors of 10~mm, and the error spectrum of the GPS estimates was approximately flicker noise. These results may however represent a best-case scenario since they were obtained over a short (~10~m) baseline, thereby greatly mitigating baseline-dependent errors, and when the number and distribution of satellites on the sky was good. For example, we have determined that the rms error can increase by a factor of 2--3 as the GPS constellation changes throughout the day, with an average value of 3.5~mm for eight identical, hourly-spaced, consecutive test events. The rms error also increases with increasing baseline, as one would expect, with an average rms error for a ~1400~km baseline of 9~mm. We will present an assessment of the accuracy of high-rate GPS based on these measurements, discuss the implications of this study for seismology, and describe new applications in glaciology.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1241 Satellite geodesy: technical issues (6994, 7969)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 1294 Instruments and techniques
DE: 7212 Earthquake ground motions and engineering seismology
SC: Geodesy [G]
MN: 2007 Fall Meeting