Assessment of IDS contribution to ITRF2020

We examine DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) position time series processed by the IDS (International DORIS Service) within “ids21wd02” reprocessing, serving as an official input into the newest International Terrestrial Reference Frame, namely ITRF2020. The ids21wd02 set includes the North, East and Up coordinate time series of the 201 stations located at the 87 DORIS sites since 1993.0. These coordinate time series were delivered by the IDS as a byproduct of the IDS contribution to the 2020 realization of ITRF (International Terrestrial Reference Frame). From a number of 201 stations distributed globally, we choose a number of 115 sites, whose time series are longer than 5 years.  Position time series are carefully pre-processed by means of removing outliers and offsets. To reliably describe the DORIS position time series, we use a time series model of long-term non-linear signal, linear trend, seasonal oscillations and a stochastic part. Both deterministic and stochastic components are determined using maximum likelihood estimation. Our analysis is performed in three different ways. Firstly, we search for a preferred noise model and demonstrate, that there is an ongoing improvement of noise parameters over years. This is related to the persisting improvement in background models, antenna types, etc. Then, both deterministic and stochastic parameters are compared to the ITRF2014 IDS solution, to find the usefulness of a newly applied models or strategies, especially to prove an impact of the new C STAREC antenna type. Finally, we compare DORIS position time series to the GPS (Global Positioning System) position time series for a number of 267 co-located stations (official input of International GNSS Service into ITRF2020); both deterministic and stochastic components are compared, with a special attention paid to the differences of velocities and their errors, as they are employed for kinematic reference frames realization or in geodynamical interpretations.