An assessment of estimates of integrated water vapor from ground-based GPSdata

A network of ground-based Global Positioning System (GPS) receivers is used to continuously obtain information on variations in the integrated water v apor (IWV) in the atmosphere. We use GPS data from 1996-1998 to compare the IWV estimates with radiosonde data. The spatial correlation of estimation errors is important when the GPS results are to be used in assimilation mod els. We study and model this effect by comparing the horizontal correlation s of the IWV time series derived from the radiosonde network and the GPS da ta analysis. Under ideal conditions this method separates the IWV features from the underlying correlation function for the estimation errors in the G PS data. A sparse radiosonde network limits the quality of the obtained res ults. We foresee continued studies including more data and simulations of t he errors associated with the GPS technique.