A Global Conversion Factor Model for Mapping Zenith Total Delay onto Precipitable Water

The conversion factor is a key parameter for converting zenith wet delays (ZWD) into precipitable water vapour (PWV) with a mean value of 0.15, and the traditional method of calculating it is to model the weighted average temperature in the process of conversion factor calculation. Here, we overcome the dependence on high-precision atmospheric weighted average temperature for mapping ZWD onto PWV and build a global non-meteorological parametric model for conversion factor G pi model by using the gridded data of global conversion factor time series from 2006 to 2013 provided by the Global Geodetic Observing System (GGOS) Atmosphere. Internal and external accuracy tests were performed using data from four times (UTC 00:00, 06:00, 12:00, and 18:00) per day throughout 2012 and 2014 as provided by the GGOS Atmosphere, and the statistical average root-mean-square (RMS) and mean absolute errors (MAE) on a global scale are 0.0031/0.0026 and 0.0030/0.0026, respectively, which only account for 1.5-2% of the conversion factor value. In addition, the observed GPS data are also used to validate the established G pi model, and the RMS of the PWV differences between the established model and the observed meteorological data was less than 3.2 mm. The results show that the established G pi model has a high accuracy, which can be used to calculate the PWV value where no observed meteorological parameters are available.