Abstract

Over the last few years a number of significant improvements in the modeling of GPS observations have been identified and implemented within standard high precision analysis packages. These improvements include the transition to absolute antenna phase center models for both satellites and antenna... Show moreOver the last few years a number of significant improvements in the modeling of GPS observations have been identified and implemented within standard high precision analysis packages. These improvements include the transition to absolute antenna phase center models for both satellites and antennas, a transition to the IGS05 reference frame, and the increasing use of mapping functions that are directly related to the current atmospheric state at a station. The COSMIC/UCAR program processes both global and regional GPS networks for atmospheric applications (www.suominet.ucar.edu). We evaluate what impact these processing changes have had on the estimation of precipitable water vapor (PWV) estimates since January of 2007. Switching to the new absolute phase center models creates roughly a 1 mm drop in PWV, with the magnitude of the change dependent on the type of antenna at the station. This switch reduces biases seen between GPS techniques and other measurement methods, including microwave water vapor radiometers and radiosonde comparisons. Effects for both global and regional networks will be presented, including a summary of each major antenna type. We also evaluate the use of ray tracing based on Global Forecast System models to generate time and location specific tropospheric mapping functions. The greatest impact of this direct mapping is seen at polar sites. Finally we will show that using a numerical weather model to estimate the weighted mean temperature of the atmosphere for computing the pi factor to convert zenith wet bending delay to precipitable water vapor has become the standard for climate studies of PWV. The effects of using NWM grids versus surface temperature and Bevis regression on both diurnal and seasonal frequencies will be presented. Show less