HR: 0800h
AN: G21B-0490    [Abstracts]
TI: Investigation of site-dependent GPS errors and monument stability using a short-baseline network of braced monuments
AU: * Hill, E M
EM: ehill@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, United States
AU: Davis, J L
EM: jdavis@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, United States
AU: Elosegui, P
EM: pelosegui@ieec.fcr.es
AF: Institute for Space Sciences, CSIC/IEEC, Barcelona, 08034, Spain
AU: Wernicke, B P
EM: brian@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, United States
AU: Niemi, N A
EM: naniemi@umich.edu
AF: Dept. of Geological Sciences, University of Michigan, Ann Arbor, MI 48109, United States
AU: Malikowski, E
EM: emalikowski@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, United States
AB: A short-baseline network that we have established at Yucca Mountain, southern Nevada, is enabling us to put new constraints on the level at which individual site motion can be detected by continuous GPS stations. We use this network to investigate and quantify aspects of the GPS error budget at a level of precision that would have been hard to imagine only a few years ago. The network consists of three GPS stations (established in 2006) with baseline lengths of ~10, 100, and 1000 meters with respect to site REPO (established in 1999). The four sites together lie along a N-S line, and have nearly identical instrumentation and setup configuration. The site with the shortest baseline to REPO (REP2) has a shallow-braced (to ~1 m depth) monument, while the remaining two sites (REP3 and REP4) and REPO are deep-braced monuments fixed into bedrock to a depth of ~10 m. This setup enables us to investigate processes affecting monument stability in a relatively controlled environment. In addition to the very short baselines, the desert environment of the area further reduces the influence of systematic errors in the results. Furthermore, the network was designed so that baselines to additional BARGEN sites at distances of ~10, 100, and 1000 km allow us to assess baseline-dependent errors over a full five orders of magnitude. Analysis of the data for the short-baseline network, using the GAMIT software, produces baseline time series with a very low level of noise (from tens to hundreds of microns). However, seasonal signals with amplitudes of ~0.1--0.5 mm are clearly discernible in some of the baseline time series, even for the shortest baselines. Surprisingly, these signals are primarily in the horizontal time series and are less evident in the vertical. Values for the RMS scatter of the daily baseline time series about simple models for the seasonal cycle are 0.04--0.16 mm for the east component, 0.06--0.18 mm for the north, and 0.10--0.48 mm for the vertical, with the higher values for the longer baselines. These numbers indicate the high precision of these measurements, but also leave us with the intriguing question regarding the cause of the seasonal signals. We will introduce the experiment, present these results, and discuss various hypotheses for the possible cause of these seasonal signals, including multipath and thermal effects.
DE: 1204 Control surveys
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1241 Satellite geodesy: technical issues (6994, 7969)
DE: 1243 Space geodetic surveys
DE: 1294 Instruments and techniques
SC: Geodesy [G]
MN: 2007 Fall Meeting