Tropospheric refraction and its influence through Zenith Total Path Delay at different IGS stations

Abstract

The propagation of the Global Navigation Satellite System (GNSS) signals through the atmosphere is affected by the electron content in the ionosphere and the air density in the electrically neutral troposphere, thus causing a signal delay and leading to errors in the GNSS observations and the estimated positions. Our research has been conducted related to the influence of the tropospheric layer of the Earth's atmosphere on signals at geodetic observation stations in the zenith direction. Since tropospheric refraction cannot be directly estimated, the signal delay has been quantified by applying several developed models. As the lowest layer of the atmosphere, the average height of the troposphere is approximately ten kilometers, and it is variable concerning the latitude of the measuring station and seasonal conditions. The tropospheric delay of the GNSS signal - Zenith Total Delay (ZTD), was analyzed on the examples of three International GNSS Service (IGS) stations at different latitudes. Two epochs in July 2022 and January 2023 for each IGS station are considered regarding seasonal differences in the atmospheric parameters. It was found that at each of the IGS stations, there is an oscillation of the ZTD amplitude with a half-day period. Different patterns were distinguished at each station, depending on the station latitude and epoch, i.e., summer or winter atmospheric conditions. For example, a random walk signal was dominant at the ROAG, San Fernando IGS station.