Unmanned Systems Technology Dec/Jan 2020 | Phoenix UAS | Sonar focus | Construction insight | InterGeo 2019 | Supacat ATMP | Adelan fuel cell | Oregon tour | DSEI 2019 | Copperstone Helix | Power management focus

38 Focus | Sonar systems bespoke vehicles safe in potentially hazardous environments or missions. For example, the US Navy’s research budget allows for the development of the kinds of high-grade autopilot needed to process this real-time acoustic data and have the UUV platform react intelligently to it. However, they may consume more power than is desirable, and their lifetime is shorter than that of FPGAs, which can operate for up to 20 years. However, industrial and commercial demand is also growing as designs emerge that require less power and space. One example is adopting FPGAs for processing to improve the sonars’ power efficiency, while carrying fewer channels to reduce the data throughput. GPUs can also provide the required processing speeds for subsea acoustic payloads (typically around 150 Mbit/s), but unlike FPGAs they consume several hundred watts more than is desirable. Multi-beam sonars USV operators working at depths of 50 to 100 m are increasingly adopting multi- beam sonars (MBSs) to increase their acquisition speeds in hydrographic and bathymetric surveys. As mentioned, FPGA technology is improving, which is encouraging wider use of pulse compression functionality. That means the frequencies of transmitted sonar pulses are modulated to correlate received pulses with their corresponding transmissions, improving the overall range resolution and signal- to-noise ratio of the MBS. Multi-beam SSSs are also now being integrated with navigation systems to help rectify any errors in the motion and navigation of unmanned marine vehicles. That adds further precision to survey data on top of GNSS and inertial measurements, while ensuring USVs and AUVs can sense and avoid obstacles. Particular attention should also be paid to progress in backscattering measurement. These are readings on the backscattering coefficients of the seafloor – the diffuse reflection of waves, particles and signals back in the direction they came from. Similar to the satellite-based scatterometry standard used to measure reflections from the surfaces of waves, a research group from the GeoHab association of marine scientists is working towards a similar standardised measurement for the seafloor backscatter coefficient. Measuring that depends on vehicle and sonar orientations as well as conditions and anomalies on the seafloor.However, MBSs have proven to be critical over the past five years to developing the necessary algorithms and procedures to produce calibrated backscatter data. By computing the amount of sound reflected by different regions of the seafloor and received by the sonar, advances in backscatter measurement will inform researchers of the relative hardness and roughness of those areas. That will hugely improve the level of detail that can be processed into 3D sonar maps. For example, using backscattering measurements will reveal whether a given area of the sea bed is coral, hard rock or mud, which means marine biologists, subsea mining prospectors and others will be able to use UUVs autonomously to identify mission-critical points of interest more easily. December/January 2020 | Unmanned Systems Technology Forward-looking sonar provides cost-effective and accurate acoustic imaging for hydrographic analysis and real-time UUV navigation support (Courtesy of Teledyne Marine) Functional innovations such as pulse compression and backscatter measurement are enabling improvements in multi-beam echosounders and fishery sonars (Courtesy of Kongsberg Maritime)