There are still yawning gaps in our interconnected world: many smaller vessels on the high seas, unable to afford or unwilling to use conventional satellite communications equipment, can still find themselves isolated. ESA is part of an ambitious effort to upgrade an existing VHF system to provide wide bandwidth two-way communications across the seas.
Google your nearest port and you will find a live map depicting ship movements. Such maps are based on the VHF-based Automatic Identification System (AIS): all commercial vessels above 300 gross tonnes and larger passenger ships are mandated to carry AIS transponders that continuously broadcast their identification and navigation data.
As well as serving as the maritime equivalent of air traffic control, AIS can also be used to send messages ship-to-ship and ship-to-shore. But it has a fundamental limitation: VHF radio signals are limited to line-of-sight horizontal range, in practice about 9 km for the smallest boats, extending up to 100 km for high-mounted antennas on the largest ships.
“Once these small vessels left sight of port, or other ships, they were on their own,” explains communication system engineer Nader Alagha. “At least that was the case until 2010, when ESA demonstrated the detection and decoding of AIS signals from satellites in orbit, which is now being followed up by commercial companies through a system called SAT-AIS, thus extending AIS coverage to deep-sea vessels operating beyond the range of terrestrial VHF.
“So while AIS was not originally intended to operate with satellites, this achievement opened up the prospect of developing a next-generation VHF maritime communications service specifically designed to integrate the existing terrestrial infrastructure with a space-based network, in order to deliver two-way communication across the planet. Thus the new system will provide an important complement to both terrestrial and satellite based AIS.
“The name of this successor system is the VHF Data Exchange System, or VDES for short. ESA is supporting industry partners from member states who are currently contributing to working groups at the International Maritime Organisation and the International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) to develop and prove its feasibility of the satellite based VDES, ahead of its proposal to the world radio conference of International Telecommunication Union in 2019.”
VDES would have the advantage of working with existing VHF infrastructure, continuing to perform the key automatic notifications function of AIS on current frequencies, while shifting messaging and other data transmission to additional frequency bands.
The system would enhance vessels’ situational awareness, allowing mariners to downlink updated charts of ice and other hazards, to transmit information such as ships’ manifests to shore, or to pass augmented navigation signals to the Arctic: the North Polar region beyond the reach of Europe’s EGNOS European Geostationary Navigation Overlay Service – whose satnav-sharpening signals are transmitted via geostationary satellites – around the curve of the Earth.
Automated machine-to-machine monitoring of equipment, maintenance planning or local meteorology reports would also be facilitated, extending the ‘Internet of Things’ to the high seas.
“ESA is currently working together with industry partners to test the downlink segment of VDES, using Norway’s NORSAT-2 satellite,” adds Nader.
“A Norwegian Coastal Authorities vessel operating in the vicinity of Svalbard is receiving and recording the signals. Follow-up analysis will show message error rates, including how transmission is affected by variations of signal strength due to the Earth’s atmosphere as well as signal reflection from the sea surface.
This test campaign began in July 2017, supported by the Norwegian Space Center, Space Norway and the Norwegian Coastal Authority.”
Different aspects of VDES will be discussed at a workshop on 16 January 2018, hosted at ESA’s ESTEC technical centre in the Netherlands. https://business.esa.int/VDES-Workshop-2018-ESA
