Recent Updates of Multi-GNSS Advanced Demonstration Tool for Orbit and Clock Analysis (MADOCA)

This paper describes the recent developments of Multi-GNSS Advanced Demonstration Tool for Orbit and Clock Analysis (MADOCA) and their evaluation. MADOCA is a software package, which has the capability of estimating orbits and clock offsets of GNSS satellites including QZSS, GPS, GLONASS, Galileo and BeiDou, developed by Japan Aerospace Exploration Agency (JAXA). The joint team named JGX consisting of the Geospatial Information Authority of Japan (GSI) and JAXA has joined the International GNSS Service (IGS) analysis centers on December 2023 and has continually been providing precise orbit and clock offset products generated with MADOCA. We introduced and evaluated three recent improvements; minimum constraint conditions, an accurate yaw-steering model for Galileo satellites and a function to output satellite attitude for precise point positioning (PPP). First, minimum constraint conditions ensure Helmert parameters between a reference coordinate frame and the one realized by the estimated station positions are zero. By incorporating these conditions into estimation process instead of fixing the station positions, it is possible to align the positions to the reference frame without distorting the geometric relationship of satellites and stations. We confirmed appropriate implementation of those conditions to MADOCA while keeping its estimation performance. Second, the attitude model for Galileo satellites published by European GNSS Service Centre (GSC) was introduced, in which the yaw rate of each satellite is kept lower than the conventional nominal yaw-steering model when the elevation angle of the Sun with respect to the orbital plane is low. We confirmed the effect of the GSC model with decrease of orbit estimation errors. Third, we implemented a function to output satellite attitude information which can be directly used for satellite antenna phase center correction and carrier-phase wind-up correction in PPP. We confirmed that the use of the output attitude for PPP reduced carrier-phase residuals.