HR: 09:45h
AN: G51D-08    [Abstracts]
TI: Can a high resolution Numerical Weather Model (NWM) improve site positions?
AU: * Niell, A E
EM: aniell@haystack.mit.edu
AF: MIT Haystack Observatory, Off Rte 40, Westford, MA 01886 United States
AU: Leidner, S M
EM: mleidner@aer.com
AF: AER, Inc., 131 Hartwell Ave, Lexington, ma 02421 United States
AB: In recent years, NWM-based mapping functions have utilized global gridded NWMs with horizontal resolutions of 50km to 200km. These have resulted in significant improvement in estimates of the hydrostatic component of the delay and estimated site positions, while little or no improvement has been realized in estimates of the wet component. This lack of improvement has been attributed to the much smaller horizontal scale for variation in the water vapor distribution ($<$1-5 km) than is represented in the global NWM (50-200 km). We have begun an investigation to 1) see if mapping functions derived from a high-resolution numerical weather model can improve the wet delay component, and 2) evaluate site position errors as a function of NWM resolution. Eventually we will look at the effects of time-varying azimuthal asymmetry, since NWMs can provide a full 4-dimensional (three spatial dimensions, plus time) picture of the distribution of mass in the atmosphere. As a first step, however, we report preliminary results using only symmetric mapping functions. Using radiosonde profiles as "truth" for calculating the mapping functions, we will evaluate site position errors (bias and RMS) for mapping functions calculated from MM5 runs at four horizontal resolutions, from 81 km down to 3 km. For our evaluation, we use the eight globally distributed sites of the CONT02 VLBI observation sessions which covered fifteen successive days in 2002 October. The effective site position errors will be calculated for the GPS constellation specific to each site. We anticipate that the results will provide guidance on the minimum resolution required for NWM-derived azimuthally symmetric mapping functions.
DE: 1294 Instruments and techniques
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting