Evaluation of the zenithal total delay estimates from BeiDou/GPS combined signals in the frame of the IGS MGEX project

In this study, done in the frame of the MGEX (Multi-GNSS Experiment) project, for 20 selected worldwide stations, and for the whole year of 2015, we compare zenithal total delay (ZTD) estimated values from BeiDou/GPS combined signals, to ZTD estimates from GPS-only signals, and also to ZTD estimates from the IGS analysis center CODE (CODE products), in order to assess the intrinsic accuracies of these ZTD estimates. We used the PANDA software from Wuhan university for all our data processing, with precise orbits (PPP) from the GFZ IGS analysis center. We found that the GPS-only ZTD estimates show a very good agreement with the CODE final ZTD products, but that a systematic negative bias of around 3 mm is showing up between the ZTD estimates from combined GPS/BeiDou data w.r.t. GPS-only data. This indicates that the accuracy of Beidou satellite orbits and clock errors still need to be improved w.r.t. to IGS standards.