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

73 telemetry links and battery voltages are as they should be. A survey control point is recorded near the launch site to ‘zero’ the vehicle when testing that GNSS readings are being received accurately. The team can also select similar control points in the water for the sonar and lidar, to ensure they are still recording known data points consistently from one day to the next. In the loop Surveying a medium-sized harbour like Newlyn or Mevagissey typically takes one or two days. Although examining the condition of quay walls is vital for users of the team’s services, plotting automated paths along them is problematic, as many boats are often moored there, and debris is often more prolific. So, when measuring the walls, the team takes closer control of the Ultra-2, directing the lidar, sonar and cameras towards areas of interest, as well as panning and tilting the cameras to look for debris around the vessel to prevent the thruster propellers from becoming clogged or jammed. “We also monitor VHF radio for traffic in the harbour, while maintaining a visual look-out from the control station,” Walton adds. “That shows what we call a ‘sounding grid’ – a 3D image of the point cloud we’re generating in real-time, enhanced with our integrated RTK GNSS. “That allows us to check for blind spots, shadow areas or missed areas, and we conduct the survey like that. Once we’re happy with coverage, we recover the USV.” To prevent straining the bandwidth requirements of the 5.8 GHz data link from the Ultra-2, the survey laptop at the control station receives just a remote desktop image feed of the QPS QINSy survey software running on the computer inside the Ultra-2, rather than the full stack of sensor data. To carry out a survey amid shallows and rocks, the team will use the sonar and lidar maps of the seabed gathered in the sounding grid thus far to approach along a safe gradient, and steer the Ultra-2 as close as possible to the rocks or shallows, but without risking damage to the sonar or the hull (keeping 0.5 m depth beneath the hull to prevent this). Once the mapping is finished, the Ultra-2 is driven to its slipway or crane, and steered (or lowered) onto its trailer for return to the workshop. Once back in the workshop, the propellers and hull are checked to make sure they’re clear of debris such as seaweed or fishing line, the batteries are recharged, and any mechanical, hardware or software adjustments to the Ultra-2 that could be beneficial to future survey quality and efficiency are considered. Post-processing In addition to RTK geo-tagging data points to 2 cm, the team also post- processes for 1 cm GNSS accuracy. “Applanix’s PosPAC MMS software mathematically infers gaps in GNSS data, to minimise any errors from the USV passing under bridges or piers,” Walton says. “Post-processing multi-beam sonar data also helps filter out ‘bad data’ from things like fish and acoustic noise that generate points that don’t actually exist.” The team will also cut out unnecessary data such as repeated points from overlaps in survey lines. This meant that in Mevagissey, for example, the amassed data went from a 250 million point cloud across 100 Gbytes of files to a 14 Gbyte folder for the customer – with about five days spent post-processing on a computer with an Intel i9-8950-HK processor and Nvidia DGX-1080 8GB GPU. Having successfully carried out surveys of medium-sized ports and bridges, Ultrabeam Hydrographic aims to learn from each mission in order to modify its vehicles, software and computer hardware. This, Walton says, will optimise the company’s ability to survey and post-process much larger harbours and rivers, even running into the hundreds of billions of point measurements. Unmanned Systems Technology | December/January 2019 To navigate shallows and rocks, the team will plot an initial approach using seabed or riverbed imagery already gathered, to keep within the 0.5 m depth margin for the safety of the USV hull and sonar