Estimation And Applications Of The Ultra-rapid GNSS Precise Clock Correction

The Global Navigation Satellite System(GNSS)provides navigation,positioning and timing services in all-time,all-weather and with high precision.It plays a more and more important role in the construction of national economy,the research of earth science,modern military struggle and other fields.The ultra-rapid or real-time GNSS precise orbit and clock products are needed in many applications,such as real-time Precise Point Positioning(PPP)and near real-time Precise Orbit Determination(POD)for Low Earth Orbit(LEO)satellites.The International GNSS Service(IGS)can offer ultra-rapid ephemeris product,the accuracy of predicted orbit is high.However,the accuracy of predicted clock is too low to satisfy the requirement of rapid precise positioning and orbit determination.This paper focuses on the GNSS ultra-rapid precise satellite clock correction estimation and application,discussing the method of clock correction estimation based on IGS ultra-rapid predicted orbit.Moreover,the performance of estimated ultra-rapid satellites clock product on determining the precise station positions and LEO satellite orbits is demonstrated.The main work and contributions of this paper include the following three aspects:First,the method of GNSS ultra-rapid precise satellite clock correction estimation is studied.This method estimates GPS ultra-rapid precise satellite clock correction using the zero-difference observations of global stations,based on the IGS ultra-rapid predicted orbit products.The results show that the accuracy of estimated ultra-rapid clock products is about 0.1 ns,which is better than that of IGS real-time clock products.Second,the performance of estimated ultra-rapid clock on determining station position using PPP method is demonstrated.Firstly,the method and process of PPP are given.Secondly,the performance of five types of products(final,rapid,ultra-rapid,realtime and the estimated clock products)for static and kinematic PPP is investigated.The results show that,the positioning accuracy of estimated clock products is equivalent to that of IGS final products,and significantly better than that of IGS ultra-rapid products.Third,the method of near real-time precise orbit and baseline determination for formation flying satellites are studied and implemented.The near real-time precise orbit and baseline of LEOs are obtained using the estimated GPS clock and IGS ultra-rapid predicted orbit products.The results show that,the single-satellite orbit accuracy of GRACE satellites is better than 4 cm(3D-RMS)using this method above.It is also shown that the orbit accuracy is equivalent to that of IGS final product,but better than that of IGS ultra-rapid and real-time products.The inter-satellite baseline accuracy is about 1 mm,which is better than that of ultra-rapid products.