Assessing the exchanging satellite attitude quaternions from CNES/CLS and their application in the deep eclipse season

Satellite attitudes that relate to the satellite antenna phase center and wind-up are essential to high-precision Global Navigation Satellite System (GNSS) data processing. However, during eclipse seasons, various attitude strategies are adopted in the different Multi-GNSS Experiment Analysis Centers (MGEX ACs), which may cause inconsistent yaw attitude errors between the network and user ends. Thus, exchanging satellite attitude quaternions are provided by the Centre National d’Etudes Spatiales and Collecte Localisation Satellites (CNES/CLS) to match the corresponding orbit and clock products. In this research, the yaw angle computation method that uses attitude quaternions is given, and the characteristic of the CNES/CLS attitude model is also described in the eclipse seasons. Experiments with CNES/CLS final orbit and clock products are processed to investigate the benefit of attitude quaternions on satellite clock estimation and precise point positioning (PPP). The results demonstrate that the differences between nominal and quaternion yaw angles can reach 360°. Compared with the nominal attitude, the statistic standard deviation (STD) of the clock difference can be reduced by approximately 70% with the attitude quaternions. Regarding kinematic PPP with nominal attitude, a large impact of approximately 20 cm can be found in the position biases. When applying the attitude quaternions, the root mean square (RMS) of the position biases can be significantly reduced and shows an approximately 29% improvement in the up (U) component. Furthermore, if the specific MGEX AC does not provide the attitude quaternions, deleting the eclipsing satellite can obtain a similar position accuracy to that of attitude quaternions strategy when the satellite geometry is strong. However, under the condition of few redundant observations, such as Galileo-only PPP, position performance of attitude quaternions strategy outperforms that of deleting strategy. Therefore, it is hoped that more ACs can provide attitude quaternions to match with corresponding orbit and clock products.