Kinematic and highly reduced-dynamic LEO orbit determination for gravity field estimation

Kinematic positions of low Earth orbiting satellites equipped with spacebome GPS receivers are widely used as input for subsequent gravity field estimation procedures. Positions relying on reduced-dynamic orbit determination, however, are often considered as inappropriate for this task, because they depend to some extent on the gravity field model underlying the orbit estimation. We review the principles of reduced-dynamic orbit determination and give the mathematical background for a very efficient estimation scheme of reduced-dynamic satellite trajectories using least-squares methods. Simulated as well as real data from the CHAMP GPS receiver are used to show the equivalence of kinematic and reduced-dynamic orbits in the kinematic limit and to present a highly reduced-dynamic orbit determination scheme as an alternative to kinematic point positioning.