Accuracy of real-time ZTD against IGS Final product

GNSS remote sensing of the troposphere, called GNSS meteorology, delivers the zenith total delay (ZTD), which can be assimilated into numerical weather prediction (NWP) models, thus improving the quality of forecasts.

Major developments in GNSS, including new constellations, precise real-time satellite products, advanced troposphere mapping functions, have a positive impact on the quality of derived ZTD. However, neither are these achievements combined in a single processing strategy, nor is the impact of other processing parameters on ZTD accuracy analysed. Hadas et al. (2020) investigate the sensitivity of real-time troposphere products on various processing parameters, i.e., functional model, GNSS selection and combination, inter-system weighting, elevation-dependent weighting function, and gradient estimation. They define the advanced strategy dedicated to real-time GNSS meteorology, which combines recommended processing parameters. Although all four GNSSs, i.e. GPS, GLONASS, Galileo and BeiDou can provide real-time ZTD solutions independently, a multi-GNSS solution with intersystem weighting reduces the a posteriori standard deviation of estimated ZTD by up to 37%. The advanced strategy allows to estimate real-time ZTD with accuracy varying from 5.4 to 10.1 mm, which legitimates for assimilation into NWP.

ZTD periodograms (top) and differential peaks in power spectrum between real-time GPS-only and Galileo-only solutions with selected periods of expected orbit-related artificial signals for GPS (green) and Galileo (blue) (bottom).

Hadas and Hobiger (2020) focus on the contribution of Galileo to real-time GNSS meteorology. The slightly worse performance of Galileo-only solution than GPS-only solution over the entire year 2019 is attributed to fewer operational satellites, Galileo outage in July 2019 and missing antenna phase centre corrections for a second Galileo frequency. However, a combined GPS+Galileo solution leads to significantly better results than a GPS-only solution. Processing of nearly twice as much observations decreases the ZTD standard deviation by a factor of 1.5–2.0. The accuracy with respect to the final ZTD products improves by 3.7% to 8.5%. Finally yet importantly, the combined solution suppresses orbit-related artificial signals of high frequency.

For details we refer to:

Hadaś T, Hobiger T., Hodryniec P. (2020): Considering different recent advancements in GNSS on real-time zenith troposphere estimates. GPS Solutions Vol. 24, No. 99, Berlin – Heidelberg 2020, pp. 1-14,

Hadaś T, Hobiger T. (2020): Benefits of Using Galileo for Real-Time GNSS Meteorology. IEEE Geoscience and Remote Sensing Letters, pp. 1-5,

Research have received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 835997 (see also