IN ACTION eNavigation Eyes in the sky


As part of our occasional series on eNavigation, we explain how satellites aid boating communications


eading up to the withdrawal of Admiralty charts, we go back to basics and explain what Global Navigation Satellite Systems (GNSS) are and how they feed into our electronic chart systems (ECS). We use satellites for a huge number of applications, from communications, location services and safety systems to TV channels. In the maritime field they provide long-range communications needed to calculate location, speed and course over the ground, receive and deliver distress messages from EPIRBs & PLBs and, in more recent times, offer long-range internet connections.


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The various satellite groups are divided into three main categories according to their altitude:


GEO (Geosynchronous or Geostationary Earth Orbit) As the name suggests, these satellites appear stationary. Technically they’re orbiting the earth but are at a great altitude (around 36,000km) so their speed matches that of the earth. This means they have the same ‘footprint’ on the earth’s surface – the ground area that the satellite covers – at all times. Between them, they cover most of the earth’s surface 24 hours a day. However, they have a permanent blind spot in the polar regions. We use GEO satellites for distress messaging and for GNSS Satellite Based Augmentation Systems (SBAS).


MEO (Medium Earth Orbit) These constellations are from 19–23,000km above the earth and have an orbit time of


“Satellites provide long- range communications needed to calculate location, speed and course over the ground”


44 rya.org.uk WINTER 2024


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