The use of W-band radar can provide cost-effective situational awareness and aid DP operations in congested offshore windfarm environments, writes Navtech Radar IA and autonomous vehicle product manager, Sam Wood
With the global offshore wind market forecast to reach 240 GW by 2030, turbines and other infrastructure will become more commonplace at sea. This exponential growth brings with it new safety challenges; the cost of deploying co-operative targets, or reference points, on every new turbine structure is prohibitive, and yet they have been essential to conventional solutions to dynamic positioning (DP).
W-band radar, with its high level of resolution and all-weather resilience, will be increasingly important in these congested offshore environments, aiding situational awareness that depends on accurate, reliable and continuous position information, essential for DP and navigation.
DP systems are invaluable for cable and pipe-laying, surveying, and other tasks required to maintain and service offshore windfarms.
“In the growing seascape of windfarms, there is a paucity of targets”
A DP-equipped vessel is reliant on its position reference sensors to enable the advanced functionality afforded by advanced computer control, falling broadly into two categories: global references; and local references. Global references are systems such as GNSS, which rely on a set of globally visible satellites or other known global reference to provide a position. Local reference systems provide a range and bearing to a local co-operative target, typically laser or LiDAR position reference sensors.
Most of these platforms are equipped with laser targets which allow the supply vessels to line up with the appropriate spot on the platform and then maintain position using DP technology. An ideal operation will allow the vessel to approach the platform using multiple local reference sensors, improving safety, redundancy, and speed of operation.
In the growing seascape of windfarms, however, there is a paucity of targets, which has meant new methods and systems are being deployed to counter the requirement to fit every wind turbine with a target, each with its own power supply, electronics and inherent vulnerabilities, not least cost. The first on the scene has been LiDAR, which measures the time difference light travels to and from the target or structure. LiDAR has proved a highly accurate aid to DP and navigation; however, it is not without its disadvantages, which is why W-band radar is required for redundancy.
W-band radar (76-77Hz) can deliver spectacular imagery and accuracy, with a 500 m range, as well as being independent of GNSS and infrastructure and highly resilient to rain, fog and glare.
Comprising a single 360° radar sensor and a small, low-power processing unit, the picture it can acquire from of its local environment can be used to output accurate odometry, in which it can build a local map of the vicinity, and then using this map, locate the position of the sensor within it.
Utilising a single high-resolution sensor, the system uses radar images alone to provide accurate motion estimation in three degrees of freedom, x, y, angle. Radar motion estimation can be used in tandem with a radar map of the area to provide absolute positioning. The system outputs NMEA style messages that can then be used by downstream systems; it also uses an innovative keypoint-based framework, ensuring centimeter-level accuracy, resilience, and reliability across diverse conditions.
In this way, the radar data can be integrated with data from other sensors, such as GPS, GNSS, inertial data, laser, camera and sonar.
Developed in the UK, Navtech Radar’s Terran360 solution can enable autonomous navigation of vessels in environments where GNSS cannot operate, in any weather conditions and day or night, enhancing vessel productivity.
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