Unmanned Systems Technology 023 I Milrem Multiscope I Wireless charging I Logistics insight I InterGeo, CUAV London & USA show reports I VideoRay Defender I OS Engines GR400U-FI I Ultrabeam Hydrographic Ultra-2 I IMUs

72 place and at depth underwater. For the Ultra-1, a pivoting ‘deployment pole’ was sunk into the water, with the sonar on the underwater end and the INS connected at the other. The Ultra-2’s catamaran design allows a similar pole to be sunk vertically between the pontoons, allowing its sonar’s depth to be adjusted without needing to tilt or pivot it, and keeping it at the CoG to compensate further for wave- induced motion. This design parameter had long been a core aim of the company, but as the Ultra-1’s hull was inflatable, creating a hole in the ‘floor’ of the prototype was not feasible. Before deployment Before a survey mission, the team fits all the required survey equipment onto the Ultra-2, and the vessel is loaded onto a bespoke trailer that is towed by a van. A mission will typically begin at a suitable slipway, although if one cannot be found the Ultra-2 can be lowered into the water by a crane if one is available. The team is also considering development of a trailer with a built-in crane, so that it doesn’t have to rely on local infrastructure for launch and recovery . High tide is the most suitable for launches, as low tide naturally poses greater hazards for the survey vehicle. Conducting surveys in daylight is also critical for safety: after a launch, a member of the team will follow the Ultra-2 around the harbour to look out for any potential hazards. The rest of the team will remain at the control station, which consists of three laptops – one for observing the survey data, one for operating the survey equipment and one for remotely operating the USV if necessary. An RTK base station is used to send GNSS corrections to the vehicle, enabling real- time geo-tagging to 2 cm accuracy. Apart from the tides, adverse weather can also delay a launch. Although the Ultra-2 (and Ultra-S, when deployed) can withstand winds of up to 80 kph, the high risk of damage to the craft and severe degradation of data quality make such conditions untenable. “Before we deploy the Ultra-2, we’ll walk the site to look for any hazards,” Walton says. “We generally use Google Maps to plan an expected route to cover the whole area, then we deploy the craft and start the survey. If it’s an open area, we can typically leave it on automated survey mode, to cover the area with minimal input from us.” The route will generally comprise straight lines back and forth across much of the survey area. Areas considered too risky for automated surveys include those with debris, waterfowl, and moored or moving boats, as well as shallow, rocky areas. Operations are carried out with a ‘man in the loop’ who will take control intermittently, doing so via four optical cameras installed on the corners of the Ultra-2 to help steer around problem areas. Before launch, the USV’s systems must be checked and calibrated. Some systems, such as the Applanix POS MV WaveMaster II inertial navigation system as well as the cameras, can be calibrated once they’ve been installed in the workshop. The lidar can be calibrated in the workshop or in the water, by conducting a patch test. That involves taking two data measurements in different directions to identify a potential roll misalignment. These angular offsets must be eliminated to integrate the survey sensors with the GNSS and INS, and put their readings into the same reference frame for timing and georeferencing. For multi-beam sonar, patch tests must be conducted in the water. A depth of at least 10 m is required for an optimal test signal. Such tests are conducted every time the lidar and sonar are installed. If they are not removed and reinstalled across days of operations, a few short pre- launch checks are conducted, but no lengthy calibrations. Basic checks include confirming that the thrusters are responding to all controls, that propulsion is being generated in the right direction, and that December/January 2019 | Unmanned Systems Technology In operation | Ultrabeam Hydrographic Ultra-2 The Ultra-2’s sonar uses a metal lattice gantry standing in place, while the central pole with the antenna bar across the top moves vertically up and down to adjust for the depth required for the echo sounder