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

81 Seafloor Systems custom HydroCat-150 | In operation cloud data – both acoustic and laser points, that is. “A second IMU integral to the Lidar would have just added unnecessary weight and power consumption. As it stands, about nine out of 10 of our USVs use Applanix or Trimble systems pre-packaged with the sonar for geo- referencing and navigation. At no point during GNSS outages [caused by bridges or other overhead structures] did the IMU fail to kick in and carry the navigation system forward via dead reckoning – and extremely accurately, at that.” As the USV travels autonomously down the waterway, the water department’s command vehicle typically uses one of the service roads running alongside to maintain visual line of sight between the vessel and its operators, for safety’s sake. Inside the customised HydroCat, the vehicle’s PC runs the popular Hypack software package for processing hydrographic survey data; a wi-fi data link then transmits it to the command vehicle in real time to the operator’s laptop (using TeamViewer as a compressed desktop interface). The operator can control and analyse the data visualisations, as well as monitor the mission’s progress, change sensor settings and double-check that the USV is still in the centre of the aqueduct’s canal. “We use a dual-chain wi-fi system from MikroTik, which gave us a throughput of 200 Mbit/s. That is enough for video, and more than enough for the amount of hydrographic and Lidar data being generated. We weren’t remotely transmitting all the data at once, just a remote desktop view of it was enough,” Tamplin adds. At water’s end Between surveys, the USV is typically carried from the endpoint of one section to the start of the next using the aforementioned boom truck, and back onto the trailer for transport back to the water department’s workshop at the end of the day. After returning the USV to the trailer, the echosounder, IMU and Lidar are disconnected, and the vehicle is returned to its workshop. “All our USVs are made from roto- moulded high-density polyethylene, which is very durable and corrosion- resistant,” Tamplin says. “And the hardware is largely stainless steel or aluminium, so maintenance pretty much never drags much longer beyond disconnecting the electronics. “We’ve provided training and support to the water department to get their folks up to speed with operating the USV. They’ve successfully used it since August last year without incident.” For the future In addition to manufacturing and training, Seafloor Systems has signed a three-year maintenance warranty (at no charge) with the department, so if there is an apparent stall in performance, Seafloor will get the custom USV into its workshops for assessment or repairs if necessary. Elsewhere in California, Seafloor is now concluding a similar project with the US Geological Survey (USGS) to build two modified versions of its HydroCat- 180s for monitoring and analysing the growing intrusion of salt water into the California Delta. “This region is the salad bowl of the US, as well as the biggest wine-growing region and one of the biggest habitats for salmon and a wide range of other fish stocks,” Tamplin notes. “Changes in salinity levels caused by seawater ingress therefore pose a dire threat to all those aspects of our economy.” The 5.5 m-long HydroCat-180s are being built with individually articulated hulls and gimballed decks – unlike the monohull or catamaran designs for most USVs – to ensure their acoustic doppler current profilers (ADCPs) can maintain a strict downward-looking angle amid the waves and swells they will experience. “Typically, the USGS will operate ADCPs on their vehicles and run them across the tide as it rises on the delta, but the tidal bore in this area is too strong and fast, which makes such readings too inaccurate. Our customised large USVs will therefore be deployed from either side of the delta and converge in the middle, to accurately correlate the tides and currents of the different waters and their salinities. “They’d used our smaller vehicles previously. One such project encompassed their first-ever autonomous ADCP cross-sectional survey, and that got them thinking about trying out our bigger vessels.” With the trial of this autonomous ADCP survey having been successfully concluded, the USGS placed an order for the two customised vehicles in late 2019. Delivery is expected shortly. Unmanned Systems Technology | August/September 2020 The Reson T50 echosounder’s firmware compensated for reverberations of acoustic pulses against the aqueduct walls to produce clear imagery (Courtesy of Seafloor Systems)