Auto-BAHN: Software for near real-time GPS orbit and clock computations

The Auto-BAHN software under development at Newcastle University aims to incorporate a near real-time capability for GPS orbits and clocks into the GPS software BAHN, currently in operational use for IGS related activities at ESOC/ESA. As a first step the deterministic least-squares batch processor in BAHN has been replaced by an Extended Kalman Filter facilitating continuous computation of GPS satellite orbits and clocks and other receiver and satellite parameters. In this paper the underlying methodology behind the Extended Kalman Filter approach is introduced as required to handle GPS phase and code data from a global network of GPS tracking stations. In addition, details are presented about the replacement of global, arc-dependent and epoch-dependent deterministic parameters by stochastic processes. Current accuracies for the GPS orbits and clocks achieved with Auto-BAHN are illustrated through comparisons with IGS final solutions.