Unmanned Systems Technology 033 l SubSeaSail Gen6 USSV l Servo actuators focus l UAVs insight l Farnborough 2020 update l Transforma XDBOT l Strange Development REVolution l Radio telemetry focus

77 To identify pre-emptively any area of damage where leaks are likeliest to occur, the water department decided in 2017 that it needed to accumulate a clear and comprehensive body of data covering the waterway, and identify any problems that could threaten the Golden State’s water supply. “They needed to find every single little crack before it could turn into a large one, every chunk of potentially harmful debris, any shifting of the concrete liner owing to soil slumping and creep. That’s where the idea came from to carry out a hydrographic survey,” Tamplin explains. To acquire the vast amount of data needed, the water department reached out to USV manufacturer Seafloor Systems to source an unmanned system to carry out the many and lengthy surveys while keeping the need for operator input to a minimum. The customised HydroCat-150 “The department has been a customer of ours for at least 10 years, using our smaller USVs for surveying the inland California Delta – another hugely important asset they need to monitor and manage – and we resell them some Teledyne products to do those surveys,” Tamplin says. “So they presented the problem to us, and after considering their requirements we agreed in 2018 to build a USV to their specifications for size and performance. Also, we proposed building it at our own cost and demonstrate it on the aqueduct to prove that it would work.” Most of Seafloor’s USVs have been built to survey harbours, reservoirs and similarly wide-open bodies of water. The California Aqueduct project, however, presented an enclosed and winding stream (confined to 100 m at its widest points, and 10 m at its deepest) which would require great accuracy and security in the survey vessel’s GNSS-INS capabilities. Even more problematic though is that the air above the water’s surface is often crossed by low-hanging power cables, overpasses, footbridges and other obstacles. “That means we had a height limit of 20 in [50 cm] above the water that we had to design for, so that the vessel could pass unimpeded under the utilities and crossings over the aqueduct, or else the vehicle would have to be retrieved every 500 m, to pick it up and carry it around an obstacle,” Tamplin says. “We also had to carry out each part of the survey in a single pass, with no going back upstream or any need for swapping equipment in and out, other than batteries perhaps. So we had to cover a 100 m-wide swathe and a 10 m vertical height above the bottom.” To ensure a full breadth of sensor coverage across these distances, Seafloor Systems selected a dual-head Reson T50 multi-beam echosounder from Teledyne Marine, which gives a swathe width of more than 20 times the water’s depth. Furthermore, a Carlson Merlin Unmanned Systems Technology | August/September 2020 Seafloor Systems custom HydroCat-150 | In operation Seafloor Systems customised one of its HydroCat-150 USVs to fit the narrow clearances and water conditions of the aqueduct (Courtesy of Seafloor Systems)