62 Show report | Oceanology International neural network is able to learn the unique dynamics of the vehicle,” he says. “For example, if you’re on a train, you start with a factory learned model and it learns the specifics of that particular train over time. The models are trained on hundreds and thousands of hours worth of real field data, and continue to learn and fine-tune the physics model in the field. This allows the system to track sensor errors far more accurately and also reject erroneous data very well.” The end result is that the company’s less costly MEMS gyroscopes achieve performances comparable with other FOGs on the market, while the performance of its FOGs is similarly elevated. With AI enhancement, INS can retain a sufficiently accurate position for the vehicle for much longer, increasing from the realm of minutes to that of hours for a MEMS INS. “This opens it up to a whole broader spectrum of capability,” Orr says. Exail presented updates to its Gaps ultra-short baseline (USBL), pre-calibrated, underwater positioning and communications system, new generations of which have been developed every five years or so since the company began working on it in 2004, according to Exail’s Paul Urvoas. USBL systems track vehicles by emitting an acoustic ping, to which cooperating vehicles respond with an identity coded ping. Receiving these responses through several channels, the Gaps unit works out the responding vehicle’s position. “We measure time difference of arrival for the distance and phase difference for the bearing,” he says. “We also compensate the acoustic ray bending that depends on sound velocity profile.” Urvoas says the latest generation consists of three products. The top-ofthe-range Gaps M7 can track cooperating vehicles down to 7,000 m deep using lower frequencies than before, and it contains a high-performance inertial navigation system (INS). Gaps M7 has a stated positioning absolute accuracy figure of 0.06% of the slant distance, with a circular error probable (CEP) of 50%. This accuracy covers the higher offshore requirements and is achieved without any in-field calibration, thanks to its embedded high-grade INS. “With this, we are taking on deep sea exploration challenges and future applications like deep sea mining and 6000 m class autonomous underwater vehicles (AUV).” Gaps M5 is similar, but uses an attitude and heading reference system (AHRS) instead of an INS to reduce cost, returning a positioning accuracy of 0.2% of the slant distance (CEP50). Finally, the smallest, lowest-cost Gaps M3 does not contain an inertial sensor as it is intended for permanent installation on vessels equipped with a gyrocompass, vertical reference unit and motion sensors. Its compactness makes it very adapted to uncrewed vehicles as well, Urvoas says. A new feature on all Gaps models is acoustic telemetry to communicate with up to 15 subsea vehicles simultaneously. “This will open up new applications such as autonomous seabed mapping, operating several AUVs at the same time and controlling data of the subsea net.” Fiberpro launched its new fibre-optic gyroscope (FOG) technology-based FN 200C, a single-box system that serves as an inertial navigation system (INS), a motion reference unit (MRU) and an attitude and heading reference system (AHRS) at the same time. The FN200C determines position, velocity, vertical and horizontal displacements, and absolute orientation (heading, pitch and roll) for any platform on which it is mounted. FN200C is an IP68-rated version of an all-new generation of ruggedised, EMC/EMO-shielded, fully integrated, high-performance, strapdown system, says Richard Ryu. Ryu says the FOG-based IMU ‘FI200C’ inside the FN200C box is a closed-loop sensor that uses feedback to minimise drift. “Of course, in very long operations there will still be some drift, but compared to open-loop solutions there is a huge difference,” he adds. One feedback mechanism is an integrated optical circuit (IOC) chip. In a FOG, rotation of the sensor causes a phase shift between the light beams travelling in opposite directions within a fibre-optic coil. This phase shift is proportional to the angular velocity of June/July 2024 | Uncrewed Systems Technology Exail’s Gaps family of ultra-short-baseline (USBL) underwater positioning and data communication systems, with the newest Gaps M3 for vessels with their own inertial sensors
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