HR: 10:50h
AN: G41C-03 INVITED     [PDF]
TI: Tropospheric errors in GPS time series
AU: * Niell, A E
EM: aniell@haystack.mit.edu
AF: MIT Haystack Observatory, Off Rte 40, Westford, MA 01886 United States
AB: Errors related to modeling the azimuthally symmetric component of the atmosphere are reflected primarily as errors in the height coordinate and in the atmosphere zenith delay. The use of in situ information about the state of the atmosphere, for example from a global numerical weather model, will reduce the errors in these parameters that are due to atmosphere estimation by a factor of about two compared to a seasonal model for the elevation dependence of the atmosphere delay. In addition to an overall reduction in scatter, the improvements at periods from annual down to diurnal are significant. How much these improvements are realized in the observed position scatter and accuracy depends primarily on the lowest elevation for which observations are included in the analysis. The uncertainty due to the atmosphere parameterization is dependent on the distribution of observations on the sky, and increases with decreasing minimum observed elevation. To be balanced against this, the uncertainties in the height and zenith delay estimates decrease with decreasing minimum observed elevation. Furthermore, the atmosphere error is a strong function of latitude, increasing by a factor of about two from the equator to 60 degrees. At the same time the height precision is decreasing due to the loss of visible satellites in the zenith direction. In order to better assess the optimum analysis strategy I will present error budgets, for minimum elevations from 5 to 15 degrees, for the uncertainties in height both for the atmosphere models currently in use and for the anticipated use of a global Numerical Weather Model.
DE: 1223 Ocean/Earth/atmosphere interactions (3339)
DE: 1229 Reference systems
DE: 1247 Terrestrial reference systems
DE: 1294 Instruments and techniques
SC: Geodesy [G]
MN: 2003 Fall Meeting