Kinematic GPS positioning of LEO satellites using ionosphere-free single frequency measurements

A method for kinematic point positioning of satellites in low Earth orbit (LEO) based on single frequency GPS measurements is discussed. It makes use of a ionosphere-free combination (GRAPHIC) of C/A code and L1 phase observations and can thus be employed with the majority of non-geodetic spaceborne GPS receivers. Other than dynamical Kalman filter schemes estimating position, velocity and clock parameters along with a set of biases for all tracked channels, a purely kinematic approach is examined in this study. It comprises a global adjustment of positions, clock offsets and pass-by-pass biases from the observations. As such, it is free of any assumptions on the motion of the user vehicle and can be applied for free-flying as well as maneuvering spacecraft. Sample results are shown for LEO GPS data collected with a low-cost single frequency receiver in a signal simulator test bed as well as flight data from the CHAMP mission. In both cases, a purely kinematic 3D position accuracy of 1-1.5 m could be demonstrated in comparison with concise reference trajectories. (C) 2003 Editions scientitiques et medicales Elsevier SAS. All rights reserved.