MADOCA: Japanese precise orbit and clock determination tool for GNSS

Abstract

The Japan Aerospace Exploration Agency (JAXA) has developed Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis (MADOCA). This tool estimates orbits and clock offsets of multiple GNSS systems (Multi-GNSS), namely GPS, GLONASS, QZSS, Galileo, and BeiDou. The orbit and clock offsets are estimated in both post-processing with iterative weighted least squares and real-time processing with extended Kalman filter (EKF) using observation data collected from the International GNSS Service (IGS) network and our monitoring station network (MGM-net). Since we began the development in 2011, we have improved the MADOCA’s performance by adopting the precise force and measurement models, the original empirical solar radiation pressure (SRP) model, and processing algorithms for stability and reduction of processing time. In the latest annual evaluation of MADOCA products in 2021, the orbit comparison with the IGS final product for the GPS and GLONASS were 2.8 and 8.0 cm (median value of daily 3D-root mean square (RMS)), respectively, and the results of satellite laser ranging (SLR) residual evaluation for the BeiDou and Galileo were 14.6 and 4.9 cm (RMS), respectively, a performance comparable to the products of the IGS Analysis Centers (ACs). QZSS products, in particular, have achieved the world’s highest level of accuracy as 6.4, 10.1, 9.0, and 10.5 cm (RMS) for the QZS-1, -2, -3, and -4 respectively in the SLR residual evaluation. This was achieved by improving and fine-tuning for the original empirical SRP models. Consequently, the position difference in those products’ static precise point positioning (PPP) reached 1.2 cm (3D-RMS). JAXA has made post-processing and real-time MADOCA products publicly available to users and is promoting experiments using MADOCA products in Japan and abroad.