GPS Meteorology: Mapping Zenith Wet Delays onto Precipitable Water

TLDR

GPS receiver networks enable remote sensing of atmospheric water vapor. The zenith wet delay measured by GPS receivers is converted to precipitable water by multiplying by a factor that depends on moist‑air refractivity constants and the weighted mean atmospheric temperature, which must be estimated a priori. The transformation error closely matches the error in the predicted mean temperature, and numerical weather models can predict that temperature with an rms relative error below 1 %.

Abstract

Emerging networks of Global Positioning System (GPS) receivers can be used in the remote sensing of atmospheric water vapor. The time-varying zenith wet delay observed at each GPS receiver in a network can be transformed into an estimate of the precipitable water overlying that receiver. This transformation is achieved by multiplying the zenith wet delay by a factor whose magnitude is a function of certain constants related to the refractivity of moist air and of the weighted mean temperature of the atmosphere. The mean temperature varies in space and time and must be estimated a priori in order to transform an observed zenith wet delay into an estimate of precipitable water. We show that the relative error introduced during this transformation closely approximates the relative error in the predicted mean temperature. Numerical weather models can be used to predict the mean temperature with an rms relative error of less than 1%.