Improved empirical coefficients for estimating water vapor weighted mean temperature over Europe for GNSS applications

Abstract

Development of the so-called global navigation satellite system (GNSS) meteorology is based on the possibility of determining a precipitable water vapor (PWV) from a GNSS zenith wet delay (ZWD). Conversion of ZWD to the PWV requires application of water vapor weighted mean temperature (Tm) measurements, which can be done using a surface temperature (Ts) and its linear dependency to the Tm. In this study we analyzed up to 24 years (1994-2018) of data from 49 radio-sounding (RS) stations over Europe to determine reliable coefficients of the Tm - Ts relationship. Their accuracy was verified using 109 RS stations. The analysis showed that for most of the stations, there are visible differences between coefficients estimated for the time of day and night. Consequently, the ETm4 model containing coefficients determined four times a day is presented. For hours other than the primary synoptic hours, linear interpolation was used. However, since this approach was not enough in some cases, we applied the dependence of Tm - Ts coefficients on the time of day using a polynomial (ETmPoly model). This resulted in accuracy at the level of 2.8 ± 0.3 K. We also conducted an analysis of the impact of this model on the PWV GNSS. Analysis showed that differences in PWV reached 0.8 mm compared to other commonly used models.