GTm-III: a new global empirical model for mapping zenith wet delays onto precipitable water vapour

Abstract

The weighted mean temperature (Tm) is a critical parameter in research of GPS meteorology. Recently, we have established two global Tm models, GTm-I and GTm-Π, using ground-based radiosonde data. These two models, which directly use the location and the day of year to calculate Tm, consider the annual cycle only. In this study, we further take into account the variation characteristics of Tm in semi-annual and diurnal periodicity and estimate the initial phase of each cycle. A more accurate global empirical Tm model called GTm-III is constructed using high-precision Global Geodetic Observing System (GGOS) Atmosphere Tm grid data, and then validated using a new set of Tm grid data, radiosonde data and Constellation Observation System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation data. Results indicate that compared to the existing global Tm models, GTm-III provides Tm estimates of high accuracy on a global scale and the predicted values are close to the true values in every moment of every day.