Development of Time-dependent mean Temperature Equations for GPS Meteorology

ABSTRACT The mean temperature is one of the key parameters in computing Precipitable Water Vapor (PWV) from Global Positioning System (GPS) measurements and is usually derived as a function of surface temperature through the use of a mean temperature equation (MTE). In this study, two new types of MTEs were developed as functions solely of the observation time so that the mean temperature can be obtained without surface temperature measurements. To validate the new models, we created one-year time series of GPS-derived PWV using the new MTEs and compared them with the radiosonde-observed PWV. The bias and root-mean-square error were on the other of ~1 mm and ~2 mm, respectively. Keywords: GPS, GPS meteorology, mean temperature equation, precipitable water vapor parameter in translating ZWD into PWV. Bevis et al. (1992) suggested that the mean temperature of the atmosphere can be approximated by the surface temperature. The Bevis model (Bevis et al. 1992) was developed using radiosonde measurements taken at 13 sites in North America. Emardson & Derks (2000) developed a model more suited to the climatic conditions of Europe. Liou et al. (2000) developed a local MTE model in addition to monthly MTEs, based on meteorological observations in Taiwan. Woo (2003) and Ha et al. (2006) developed local MTEs based on radiosonde observations in South Korea. All the MTE models mentioned in this paragraph are given as linear functions of the surface temperature and thus temperature-measuring devices should be co-located at the GPS siteIn this study, we propose two new types of mean temperature models, in which surface temperature measurements are unnecessary. The novel concepts behind the newly developed MTE models are introduced in the following section and validation results through the error analysis of GPS PWV values obtained with new models are described in Section 3.