Assisting ship navigation with an accurate and robust solution
The challenge
Around 90% of the world’s goods are carried by sea, and with a growing population and global trade demands, there is now strong interest in and investment into autonomous vessels. This is driven by a desire to reduce operating costs, boost efficiency and reduce environmental harms.
The maritime industry currently relies very heavily on global navigation satellite system (GNSS) technologies to assist vessel navigation, but while GNSS is well established it is not, on its own, fit for use with developing technologies. For example, GNSS must be combined with other positional sources (such as lidar, cameras or sonar) to achieve the near-100% availability that is required for safe autonomous shipping.
Most GNSS systems cannot provide positional accuracy to less than 10 metres when they are close to large objects. This is due to signal blocking and multipath errors (the latter occur when satellite navigation signals are reflected off nearby structures such as bridges, buildings and other ships). Jamming or spoofing of GNSS signals also present a risk. Jamming is a form of interference from external signals such as radio waves or cellular communication links, while spoofing is a type of cyber-attack, in which intentionally incorrect information about a ship’s location or time zone is communicated to a ship on an identical frequency band. These signals can lead navigation systems to make inappropriate decisions and leave them vulnerable to theft or hijacking.
For example, in 2017, 20 ships in the Black Sea were affected by a spoofing attack that is believed to have come from Russia. A fake signal quoted the ships as having an identical location 32 km inland. In this case, no people or vessels were harmed, but it is a clear indication of the threat that spoofing poses.
Of course, attempts have been made to overcome the issues surrounding GNSS navigation. Typically, these use onboard sensors for a more local approach. The most commonly used are cameras and lidar, both of which – in certain operating windows – provide detailed information about the vessel's environment. However, these sensors also have limitations, and create vulnerabilities. Cameras and lidar have limited detection ranges and can struggle with the adverse weather conditions often present in marine environments, such as fog and rain. Glare from light reflected from the water’s surface, or when the sun is low in the sky, can also be problematic.
Fortunately, there are now alternatives to GNSS systems. In particular, radar-based localisation is a novel approach with great potential. It is both accurate and robust, and can overcome the shortcomings of GNSS and other sensor solutions. Navtech Radar has recently developed a radar-based approach to vessel localisation that uses W-band radar (76–77 GHz). This provides both the range and reliability of traditional marine radar and the accurate data yielded by alternative sensor solutions.
Navtech Radar has already conducted trials on marine vessels that illustrate the power of their radar system to provide accurate vessel positioning (Figure 1). That system is called Terran360.
How will it work?
Terran360 is Navtech’s localisation solution and, for autonomous vessels, it answers the question ‘where am I?’. Terran360 is born of a collaboration between Navtech (which provides the patented 360o imaging radar technology) and another Oxford based company, Oxbotica (which provides the system’s world leading radar localisation algorithms).
Terran360 works by building a radar map, which allows it to specify the vessel’s position with centimetre level accuracy, using just a single sensor. Terran360 does not need a global positioning system or any infrastructure: it comprises a single 360° radar sensor and a small, low-power processing unit. Typical maritime applications for Terran360 range from small, un-manned surface vessels on inland waterways to large cargo ships navigating ports.
Figure 1: Navtech Radar onboard a vessel, carrying out a localisation trial with BAE systems
Benefits
Terran360 can permit the autonomous navigation of boats in environments where GNSS cannot operate, in any weather conditions and at any time of day (or night). This improves vessel productivity, since it allows work 24 hrs a day without worry about unreliable GNSS positioning or sensor failures. What’s more, when vessels take the most efficient routes they produce fewer emissions – so Terran360 can also help operators to achieve their sustainability goals.
Other benefits include:
- GNSS-free: Terran360 is a robust localisation solution that lets any vessel know where it is, in any environment, based solely on radar data.
- No infrastructure-required: zero dependence on external systems makes deployment simple, fast and cost-effective.
- Designed to be flexible and integrate into existing autonomy stacks and sensor solutions: this includes GNSS, inertial data, laser, camera and sonar SLAM solutions.
Expected technical performance
Thanks to Navtech’s radar technology, Terran360 can work at ranges up to 500m from infrastructure and functions in all weather conditions. Terran360 can be either used as a primary localisation solution or in tandem with a GNSS system during periods of outage to maintain centimetre level positional awareness. Terran360 can build its radar maps with GNSS co-ordinates, such that live positions can be reported in a global co-ordinate frame of reference.
Terran360 is easy to operate and integrate, with a simple web interface for set up and outputs provided over UDP as a NMEA-style string. Its radar maps are robust and resilient in a marine environment, even in the face of boat movement and shoreline constructions (instances where camera and laser sensors may fail).
Terran360 gives you:
- Reliable and pinpoint-accurate localisation, with positional accuracy of <10cm.
- Ability to operate in even the harshest weather conditions present in marine environments. Unaffected by rain, fog, splash or changes in lighting.
- Single sensor solution: 360°, long-range radar.
- Real time positional data provided at up to 8Hz.
- GNSS-free and infrastructure-free.
- Off-the-shelf solution, easy to integrate.
- Quick and cost-effective implementation provides a competitive advantage.
The trial
Radar-based localisation – with BAE Systems – River Thames, London UK (2021)
BAE and Navtech Radar collaborated to trial Terran360, using data collected from BAE’s data collection vessel along a stretch of the River Thames. System performance was benchmarked against an onboard GNSS with corrections, and particular attention was paid to areas of GNSS denial, such as under bridges and during sharp turns.
BAE Systems chose a 25.8-mile stretch of the Thames as the trial location; this contained 18 bridges and two sharp turns. One complete traversal of the route was conducted in order to build a map of the environment, then a second was completed to localise against it.
Terran360 uses around 10MB/km of space for map building, thus less than 3.5 GB of space would be needed to map the entire River Thames. The results of the trial showed that Terran360 provided successful localisation, with an average of 10.3 cm accuracy throughout the journey. Terran360 localised the complete length of the journey, including throughout areas that are typically challenging to sensor-based localisation techniques.
Even when off map, with distances up to 50 m, Terran360 could still localise itself in the radar map as well as in feature sparse locations where landmarks were up to 300 m away. Figure 2 shows the high-resolution data that Terran360 provided, using Navtech radar.
Figure 2:
Raw radar data collected on the test vessel, overlaid on a satellite image of the same location.
Figure 3:
Radar point clouds (shown by blue and red dots) extracted by Terran360 to localise vessel position within the environment.
Landmarks were then extracted from the radar data (see Figure 2, above) and used in odometry, scan to scan motion and localising back to the map. This is shown in Figure 3.
Navtech also compared Terran360’s yaw estimates with GNSS headings, then compared this across the localisation run. Results are shown in Figure 4. Five areas along the route were found to have spike in error. GNSS estimates can be seen to jump significantly at the exit of a bridge and when the boat makes a sharp turn. In contrast, Terran360 continued to localise successfully, providing accurate positioning in all of these locations.
Figure 4: Radar odometry integrated yaw vs GNSS heading (Top). Locations of instances of GNSS estimation jumps (Bottom).
This trial demonstrated the capability of radar-based localisation, which gave an average accuracy of 10.3cm throughout the journey. When directly compared to GNSS, Terran360 provided superior localisation under bridges and during sharp turns.
Navtech Radar is now looking for partners within the marine industry, willing to collaborate on proof of concept trials using our radar sensor for localisation, perception, anti-collision and obstacle detection.
As an early adopter of this technology, you will influence the development of the solution for your particular application, while benefiting from the software, research and development and commissioning expertise that Navtech Radar has to offer. Please contact us to discuss your trial of this new technology.
Contact us to discuss the opportunity to trial our technology.
