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97 Ocean Business 2019 | Show report satellite constellations and the major marine correction services such as Veripos Apex and Marinestar by Fugro,” said Laurent Le Thuaut. “While compact in size, the AsteRx-U supports all wireless comms available today as well as UHF radio.” It measures 174 x 166 x 53 mm, and weighs 1.5 kg. It features the company’s latest algorithms for interference detection and mitigation, multi-path rejection, and for maintaining tracking accuracy amid increased mechanical vibration or ionospheric activity. “The AsteRx-U Marine is an offshore- focused product, with particular development attention given to accuracy and reliability in difficult environments,” Le Thuaut explained. “For example, to mitigate multi-path errors we have an in-house database containing thousands of records of field GNSS measurements, so we can leverage that to correct the observed satellite signals.” Silicon Sensing is working on a series of new IMU products for maritime navigation, to be released after mid-2019. “A lot of our marine users have been requesting additional information to be output from these new products,” said Andy Hughes. “These include pitch, roll and heading measurements alongside the normal angular rate and linear acceleration measurements. “Enabling that is a matter of working on the mathematical operations and Kalman filter necessary for pitch, roll and heading derivation from the compensated sensor inputs, which will also include magnetometers and barometer measurements. That means the Kalman filter has to be optimised to reduce the sources of errors that can degrade the derived roll, pitch and heading measurements.” The company is also developing new sensors for use in future generations of its IMU, with the aim of working towards a product that would be capable of gyro- compassing without the need to rely on magnetic sensors. Impact Subsea exhibited its ISS360, which at the time of writing is the smallest imaging sonar available. It is about 72 mm long and 43 mm in diameter, while weighing roughly 400 g in air and 300 g in water. “It is a scanning sonar that provides imagery to a range of about 90 m away from the host vehicle,” said Ben Grant. “Uniquely for scanning sonars it does not use slip rings to couple the transducer to the electronics. “The transducer is fully inductively coupled to the electronics, which means it can keep scanning and never wear out. That removes the maintenance requirement to return to the manufacturer for new slip rings to be fitted, which is an issue with most scanning sonars these days.” The sonar also has integrated gyroscopes, accelerometers and magnetometers to provide heading, pitch and roll, and assist in imagery clarity by compensating for them. That helps to reduce any blurring of image data if the host vehicle rotates quickly. “The size of the system made development challenging,” Grant said. “The electronics take up a very small area inside the enclosure, with three PCBs, each six layers thick, and miniaturising everything in the boot end required complex and rigorous design work.” Unmanned Systems Technology | June/July 2019 The Impact Subsea ISS360 is said to be the smallest imaging sonar currently available Silicon Sensing MEMS IMUs