Issue 37 Unmanned Systems Technology April/May 2021 Einride next-gen Pod l Battery technology l Dive Technologies AUV-Kit l UGVs insight l Vanguard EFI/ETC vee twins l Icarus Swarms l Transponders l Sonobot 5 l IDEX 2021 report

8 Platform one HydroSurv is working with Sonardyne to gather data from offshore wind farms using an unmanned surface vessel (writes Nick Flaherty). The project will see HydroSurv use its fully electric REAV-40 platform to collect data from sensors on the seabed using an acoustic modem. The REAV-40 has a 40 kWh lithium- ion battery pack powering twin, independent 4 kW motors to give a mission time of up to 48 hours. It is designed to be lowered from a larger survey craft to collect the data, and uses a mesh IP radio to link back to the main craft for the data collection. “A big part of the proprietary development was to provide our own architectures to retrieve the data from the vessel,” said David Hull, chief executive of Hydrosurv. “Some of that will come from Sonardyne, some from ours,” he added. “We will gather and organise the data on the vehicle, and upload it to the cloud in a managed way, but that has still to be defined and would depend on the comms system,” said Hull. One challenge is that the large metal structures of the wind turbines disrupt GNSS satellite navigation, so additional inertial navigation systems (INSs) are needed, as well as a Doppler Velocity Log to measure the position of the craft relative to the turbines. The vessel uses two sensor systems from Advanced Navigation – the Certus GNSS/INS and the Spatial Dual INS system – which combine temperature- calibrated accelerometers, gyroscopes, magnetometers and a pressure sensor with a dual-antenna RTK GNSS receiver for more accurate positioning. This requires more complex sensor fusion algorithms to be developed and combined with a command & control system. The twin motors, from Torqeedo, can be controlled independently to provide more accurate positioning. The sensor fusion and control software will run on a processor board linked to the Torqeedo battery management system. The board is based on the Spectre autopilot and includes various interfaces that enable it to communicate with vehicle sensors, vehicle actuators and a front-end workstation PC. It provides a positioning accuracy of 10 to 15 mm. HydroSurv is still discussing which Sonardyne sensors will be used. Marine vehicles April/May 2021 | Unmanned Systems Technology Wind farm data collector The REAV40 will use an acoustic modem to collect data from offshore wind turbines