Evaluation of GPS/BDS-3 Satellite Attitude Products and Impact on Precise Data Processing

Objectives: Satellite attitudes have a significant impact on GNSS (global navigation satellite system) precise data processing. IGS (international GNSS service) analysis centers (ACs) have been publishing satellite attitude products in quaternion form using the ORBEX (ORBit EXchange) format. Methods: The GPS/BDS-3 satellite attitude products from 4 MGEX (multi-GNSS experiment) ACs spanning the year of 2023 are collected. Based on satellite attitude quaternions, the yaw angles of GPS/BDS-3 satellites were computed and compared using corresponding conversion formulas. The differences of yaw angles during the satellite yaw maneuvers were emphatically compared and analyzed. Then, the GPS/BDS-3 precise satellite clock estimation and precise point positioning were conducted using 122 global MGEX tracking stations, the impact of satellite yaw attitude on GPS/BDS-3 precise data processing was investigated by comparing the results using different attitude products. Results: Comparing the quaternion yaw angles from WUM (Wuhan university), GFZ (GeoForschungsZentrum), COD (center for orbit determination in Europe) and CNES (centre national d’etudes spatiales), we can find that different attitude models are adopted by different ACs during yaw maneuvers. The model adopted by GFZ differs significantly from others’, and the yaw angle differences can be up to 180° while abnormal jumps are observed. Except for GPS IIF satellites, the models adopted by WUM and COD are consistent in general. Compared with the nominal attitudes, attitude products can significantly improve the continuity of the GPS/BDS-3 satellite clock estimation and can reduce the standard deviation of the clock quadratic-differences by 85% when opposite yaw directions between the quaternion and nominal attitudes are observed. Kinematic precise point positioning (PPP) experiments show that inconsistent attitude models can cause positioning deviations by affecting the satellite antenna phase center offset and phase wind-up corrections. The attitude products can achieve 31%, 20%, and 28% accuracy improvements for the east, north, and up components, respectively, compared with the nominal attitudes. Conclusions: We recommend that users need to use satellite attitude products matching the corresponding orbit and clock products for GNSS precise data processing.