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Using radar to confront the challenges facing autonomous vessels in GNSS-limited environments

An estimated 90% of the world’s goods are transported by sea, and with populations growing and global trade expanding, the volume of goods being traded in this manner is set to triple by 2050. The maritime industry is now experiencing a wave of investment into, and exploration/adoption of, autonomous ship navigation – all with a view to creating a modern transport system that is cheaper, safer and greener than the one we have now.

Currently, GNSS-navigation plays a crucial role in the navigation of marine vessels – but it is a limited and imperfect approach. Most GNSS systems cannot provide positional accuracy to less than a metre when close to large objects – this is due to multipath issues, making it hard for vessels to navigate ports, inland waterways and offshore windfarms. What’s more, GNSS accuracy can also be affected by interference (intentional or otherwise) from external signals of the same frequency band.

Current solutions

Often, vessels use onboard sensors to cope where GNSS cannot. The most commonly used sensors are cameras and lidar. These have been successful in land-based autonomy projects, and can provide rich data concerning a maritime vessel’s environment. However, cameras perform poorly in unfavourable weather or lighting conditions, whilst lidar lacks the range required for marine autonomy.

Clearly, the maritime sector needs a single-sensor approach that can accurately provide positional information, whilst enduring tough conditions and environments.

Radar-based localisation

Navtech Radar has recently developed an approach to autonomous navigation that uses W-band radar. Unlike conventional X-band marine radars (8–12GHz), Navtech sensors use signals in the microwave frequency (76–77GHz). This creates a much clearer picture of the local environment.

Terran360 uses radar data to build up a map of a particular route, and on subsequent runs, radar data is used to localise a vessel’s position within this route, providing centimetre-level precision.

This approach to localisation distinguishes itself from alternative solutions that use GNSS, lidar and cameras in the following ways:

  • Range: Navtech’s radars have a range of up to 500 m.
  • Environmentally robust: radar-based localisers are unaffected by changes in weather or lighting.
  • GNSS-free: radar-based localisation continues to work in GNSS-denied environments, such as ports or inland waterways. There is also no risk of interference.
  • Precision: The system can assess vessel position with centimetre-level accuracy.

Radar’s advantage as a sensor is most pronounced in harsh environments. Thus, it makes sense to apply Terran360 to the maritime industry, where conditions are generally harsh and unpredictable. Radar-based localisation is a lesser-known approach that now, with changing demands, shows great potential. It is accurate and robust, and overcomes the problems arising from GPS and alternative sensor solutions.