Impact of individual antenna phase center models and multi-GNSS observations on tropospheric estimates

In this study, we investigate the impact of GNSS antenna calibration models and multi-GNSS observations on the quality of the tropospheric estimates. The accuracy and homogeneity of the Zenith Total Delay (ZTD) time series estimated from ground-based GNSS data strongly depend on the processing strategy. These factors significantly imply the GNSS solution performance; however, their impact on the quality of the derived ZTD series used for climate applications has not been comprehensively investigated.

We analyzed three years of ZTD time series obtained from GNSS data processing and afterward converted integrated water vapor (IWV). Nine different processing strategies distinguished into three groups were employed: the 1st group of solutions was obtained by applying the International GNSS Service (IGS) type mean Phase Center Correction (PCC) models (IGS14); in the 2nd group, PCC models from individual field robot calibration were used; in the 3rd group of solutions, an anechoic chamber calibration was applied. Each group of solutions was processed three times using different GNSS constellations, namely GPS-only, Galileo-only, or combined GPS+Galileo.

The results reveal that the impact of employed GNSS constellations on the accuracy of the ZTD time series is more pronounced than the impact of antenna calibration models. However, the latter factor is also noticeable and thus cannot be neglected. Moreover, validation against climate reanalysis data confirms that all approaches provide high-quality tropospheric delays.

The outcomes also indicate that ZTD estimates obtained with robotic and IGS14 calibrations are closer to that of ERA5 reanalysis than estimates derived when using calibrations in an anechoic chamber. In addition, multi-GNSS-derived tropospheric parameters are more comparable to the benchmark ones from ERA5 than those provided by single-system solutions. The results also depend, among others, on the stations' equipment (receiver and antenna).