Tracking requirements for precise ERS-1 orbit determination

Tracking equipment on ERS-1 and alternative tracking concepts are described. Orbit determination error analyses for a 3-day arc of tracking data acquired by global tracking networks are discussed. The orbit is not ideal for the investigation of the global ocean circulation. The Precise Range and Range Rate Experiment (PRARE) tracking is seriously handicapped if not more than the four currently approved systems are deployed. The major error source in computing multirevolution ERS-1 orbits is the Earth gravity field model. To achieve the highest orbit accuracy a tailored gravity model must be derived by processing the tracking data acquired during the first months in orbit. During this initial phase the tracking should be performed by the existing world-wide network of laser stations, augmented by 5 to 15 PRARE systems. Altimeter measurements should be used as tracking data.