GNSS Orbit Determination and Time Synchronization

This chapter discusses the generation of precise orbit and clock information using ground- or space-based observations. Evidently, orbit determination and time synchronization (ODTS) is an integral part of the control system of any global or regional navigation satellite system (GNSS/RNSS) provider, where the motion of the satellites and the variation of their clock must be continuously observed, predicted, and distributed to the user as part of the navigation message. Key aspects of batch and sequential estimation methods in the context of orbit and clock determination are presented. The chapter provides an overview of representative ODTS systems and the various types of GNSS orbit and clock products made available to users in postprocessing or real time. It also discusses strategies for validating the precision and accuracy of these products as a contribution to GNSS performance monitoring and product quality control