HR: 11:50h
AN: G41C-07    [PDF]
TI: Development of an in situ Antenna and Multipath Calibration System for GPS Geodesy
AU: * Park, K
EM: kdpark@kao.re.kr
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 United States
AU: * Park, K
EM: kdpark@kao.re.kr
AF: Korea Astronomy Observatory, 61-1 Hwaam-dong Yuseong-gu, Daejeon, 305-348 Korea, Republic of
AU: Elosegui, P
EM: pelosegui@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 United States
AU: Davis, J L
EM: jdavis@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 United States
AU: Corey, B E
EM: bec@haystack.mit.edu
AF: MIT Haystack Observatory, Off Route 40, Westford, MA 01886 United States
AU: Niell, A E
EM: aen@haystack.mit.edu
AF: MIT Haystack Observatory, Off Route 40, Westford, MA 01886 United States
AU: Jarlemark, P O
EM: per.jarlemark@sp.se
AF: SP Swedish National Testing and Research Institute, Box 857 SE-501 15, Boras, 00000-0000 Sweden
AU: Normandeau, J E
EM: jnormandeau@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 United States
AU: Meertens, C E
EM: chuckm@ucar.edu
AF: UNAVCO Facility, P.O. Box 3000, Boulder, CO 80307 United States
AU: Andreatta, V A
EM: victoria@ucar.edu
AF: UNAVCO Facility, P.O. Box 3000, Boulder, CO 80307 United States
AB: Geophysical applications of the Global Positioning System (GPS) for studies such as global sea level change and glacial isostatic adjustment require very high accuracy ($\sim$1 mm/year) determinations of site velocity, especially of its vertical component. However, site-dependent errors such as antenna phase-center variations, multipath, and scattering can have a significant effect on high-precision GPS applications. Despite the many efforts devoted by investigators to the calibration of those site-dependent errors, determination of these errors has proven to be elusive, since no method has been developed to measure these effects accurately in situ. We have designed and constructed a prototype antenna and multipath calibration system (AMCS) to obtain such in situ corrections. The AMCS consists of a parabolic antenna that is relatively free from these site-dependent errors. We obtain phase corrections for these errors by forming the difference between the carrier-beat phase from the GPS antenna to be calibrated and the AMCS antenna. Preliminary ``sky maps" of the antenna phase and multipath contributions show root-mean-square (RMS) phase variations that are a factor of ten or more greater than the AMCS noise system we expected. To explore the source of this noise, we acquired observations over small (few degrees) patches of the sky. From the analysis of these experiments, we conclude that the source of the phase variations is antenna and multipath errors that vary $\sim$5 mm over small changes in satellite direction. Thus, for example, differences of 1$^\circ$ in elevation angle can result in several mm variations in phase. Similarly, small variations in azimuth angle can also result in significant phase variations. We have also observed day-to-day mm-level changes in the calibration. We hypothesize that these phase variations are due to changes in multipath caused by changes in the local electromagnetic environment associated with, e.g., weather.
DE: 1200 GEODESY AND GRAVITY
DE: 1243 Space geodetic surveys
DE: 1294 Instruments and techniques
DE: 1645 Solid Earth
DE: 6914 Electromagnetic noise and interference
SC: Geodesy [G]
MN: 2003 Fall Meeting