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Changing tides and waves mean the ‘landscape’ is never the same twice, while underwater obstacles threaten boat bottoms and submarines. This is especially true around the entrances to ports and harbours, where busy shipping lanes converge over uneven seafloor topography filled with rocks and reefs.
To compound the issue for submarines and unmanned underwater vehicles (UUVs), GPS signals cannot penetrate water. So craft have to surface frequently for GPS ‘fixes’, and this requirement increases in the varied terrain of coastal waters – but surfacing brings the risk of collision. Conventional navigation involves monitoring velocity between fixes, but vehicles can end up hundreds of metres off course as the water moves around them.
A new UUV project from the National Oceanography Centre (NOC) in Southampton aims to tackle the issue using Northstar, a fully autonomous navigation system from TP Group. The project will integrate Northstar onto Autosub Hover One, a craft developed at the NOC, to demonstrate autonomous navigation and control for long periods without frequent GPS fixes.
4D awareness
The Northstar system started with a ‘meta-heuristic algorithm approach’, also known as multi-factor optimised navigation. “Rather than just saying ‘Get me there’, caring about your fuel efficiency, your risk awareness, your mission parameters, whatever it might be… producing routes that can blend all of those together,” said John Shimell of TP Group.
This multi-factor approach is combined with the requirement to operate in ‘GPS denied’ areas. To tackle the issue, the team converted S57 navigation charts from the UK Hydrographic Office into computer-readable files. The system combines the 3D charts with tide and weather forecasts, and overcomes the GPS issue using simultaneous localisation and mapping (Slam). The project is developing sonar technology for Slam measurements, which are compared with the hydrographic data and augment conventional Doppler velocity and motion logs. The result is an advanced autonomous navigation system, fusing realtime and reference data to create a “synthetic environment”. TP Group said the 4D awareness enables dynamic and realtime navigation, routing and collision avoidance in “any environment”.
From sea to air
The technology could be used in a wide range of submarine applications – surveying marine habitats or monitoring renewable energy installations.
The NOC project, which received £400,000 from the Ministry of Defence, started in March. For TP Group, however, Northstar is far more than just a marine navigation system. Its combination of realtime and reference data is also hugely applicable in the air and on land.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.