Improved Empirical Coefficients for Estimating Water Vapor Weighted Mean Temperature over Europe for GNSS Applications

Baldysz Baldysz,Nykiel Nykiel

doi:10.3390/rs11171995

Baldysz Baldysz, Nykiel Nykiel

Open Access

https://doi.org/10.3390/rs11171995

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Journal: Remote sensing	Publication Date: Aug 23, 2019
Citations: 7	License type: CC BY 4.0

Affiliation: Gdańsk University of Technology

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.

Highlights

Earth’s atmosphere affects electromagnetic global navigation satellite system (GNSS) signals by delaying their propagation
The possible dependency between Tm − Ts coefficients and the time of day were investigated, e.g., by Mekik and Deniz [19]. They proved that the differences in root mean square error (RMSE) values obtained based on coefficients estimated during day and night are not significant, amounting to about 0.2 K, for RS stations located on the Turkish territory
We considered the impact of our computed coefficients on precipitable water vapor (PWV) calculation at both RS and GNSS stations

Summary

Introduction

Earth’s atmosphere affects electromagnetic global navigation satellite system (GNSS) signals by delaying their propagation. ZHD can be accurately modeled using total air pressure at the GNSS antenna location [9], while Tm can be obtained based on the linear relationship with the surface temperature (Ts): Tm = a · TS + b. This relationship ( named Tm − Ts) was firstly proposed by Bevis et al [1]. In their model, the a (slope) and b (intercept) coefficients were calculated on the basis of 8712 radiosonde profiles made on 13 U.S stations over a two-year period.

Data and Methodology

Results and Discussion

Impact of the New Coefficients on the PWV Estimated at RS Stations

Conclusions