The impact of non-nominal yaw attitudes of GPS satellites on kinematic PPP solutions and their mitigation strategies

The yaw attitudes of Global Positioning System (GPS) satellites are critical to both satellite antenna phase centres and the phase wind-up corrections. However, the nominal yaw attitude of GPS satellites can barely be maintained during eclipse seasons. Thus, several yaw attitude models have been developed by the International GNSS Service Analysis Centres (IGS ACs) to avoid positioning degradation caused by non-nominal yaw attitudes. Based on the analysis of the strategy of each AC, the modelled yaw attitude is compared with the nominal one, and the residuals of Precise Point Positioning (PPP) are investigated to evaluate the influence of non-nominal attitudes with over one year of observable data collected from 15 IGS stations. The results suggest that non-nominal attitudes of BLOCK II/IIA satellites have the largest impact of about 20-30 cm, and their positioning accuracy can be improved by 20%-30% with the corresponding yaw attitude model. Similar results have also been demonstrated with BLOCK IIR and BLOCK IIF satellites. Furthermore, compared with the strategy of directly deleting the data for the eclipsing seasons, PPP with the yaw-attitude model achieves better results by about 30% when the satellite geometry is relatively poor.