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Galileo: following the trail of the dragon-ships
Ancient manuscripts record Viking navigators relied on 'sunstones' to find their way - archaeologists believe these may have been polarising crystals to pinpoint the Sun even in overcast skies.
By contrast, Belgian frigate Leopold I-F930, participating in the end-of-year trials, carried the most up-to-date equipment possible, with multiple Galileo receivers for both its public Open Service (OS) and secure Public Regulated Service (PRS).
"Galileo is in a transition between its In-Orbit Validation (IOV) phase and follow-on Full Operational Capability phase," explains Miguel Manteiga Bautista, head of ESA's Global Navigation Satellite System (GNSS) Security Office.
"This means we are engaging in all kinds of experimental demonstrations of all Galileo services, in particular PRS, which offers the most highly accurate positioning and timing performance, but with access strictly restricted to authorised users."
The frigate sailed first from the Dutch marine base of Den Helder on 4 December 2013 to Stavanger in Norway. From there it progressed north in very rough seas with 10 m-high waves, coming close to the Arctic circle on 17 December - a first for Galileo PRS observations - before heading home.
The testing provided tangible in-situ evidence of Galileo signal stability across both its operating frequencies up at high latitudes, equalling low satellite elevations in the local sky.
Following the completion of earlier road, then flight, testing last summer and autumn, the last challenge for Galileo's IOV phase was to engage in a long-term maritime trial into high latitudes.
The testing was performed as part of the 'PRS Participants to IOV' project jointly managed by ESA and the European Commission, in collaboration with the European GNSS Office Agency and several Member States possessing PRS test receiver technology.
The trials were performed by the Royal Military Academy of the Belgian Ministry of Defence, the UK Space Agency in collaboration with satnav-specialist company Nottingham Scientific Ltd and ESA, serving to ensure PRS signals were available whenever the four Galileo satellites currently in orbit came into view.
A dual test setup was fitted to the frigate at Den Helder. Belgium connected a PRS receiver and an OS receiver, both manufactured in Belgium by Septentrio NV, to a common antenna. The PRS receiver recorded raw PRS measurements on both frequencies while the OS receiver logged data from openly available Galileo, GPS and Glonass signals at one-second intervals.
Nottingham Scientific installed its Ultra system configured to record radio-frequency samples, allowing the detailed post-processing of Galileo OS and PRS signals.
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