Page 31: of Marine Technology Magazine (July 2024)

? ber optic gyroscope (FOG) can now weigh less than a standard 80µm cladding but also with a smaller cladding of three kilograms, less than two kilograms even, and be only 60µm for even smaller footprint gyros.

A less than 200mm in diameter. Subsea, Maxime Le Roy, Subsea Inertial Navigation Sys-

As their host AUVs themselves shrink, FOGs are following tems Product Manager at Exail, says the market is moving to suit, and as the AUVs go deeper and perform a wider range of smaller AUVs that are versatile, powerful and agnostic to any data collection tasks, FOGs continue to be part of the GNSS- situation. Exail sold the ? rst of its latest model, Phins 9 Com- denied navigational systems that enable them to do it. pact, to Bedrock for a new modular AUV designed for swift

The FOG sensors in an inertial navigation system measure deployment in geophysical surveys and monitoring. Equipped changes in orientation of the AUV to support navigation by dead with multibeam echosounder, side scan sonar and magnetom- reckoning as satellite systems such as GPS are not available sub- eter, the AUV boasts a 300m depth rating and 12-hour endur- sea. FOGs operate by monitoring the difference in propagation ance surveying at three knots with all systems operational. time between beams of light traveling in clockwise and counter- The Phins 9 Compact adds just 1.2kg to the payload and fea- clockwise directions about a closed optical path. Two beams of tures a power consumption of less than 7W. It has a Doppler light are sent in opposite directions in a ? ber optic coil. As the ve- Velocity Logger-aided position accuracy of heading accuracy hicle rotates, the beam travelling against the rotation experiences of 0.07° and pitch and roll accuracy of 0.01°. “The Phins 9 a slightly shorter path delay than the other beam, a phenomenon Compact is an ideal solution for new generation AUV manu- called the Sagnac effect. The difference in phase shift between facturers and e-ROV operators looking to save power without the two beams is used to estimate the rate of rotation. In an in- compromising on data processing capabilities,” says Le Roy. ertial navigation system, there will be three FOGs, each aligned Its applications include survey-grade coastal and offshore sea- orthogonally and combined with accelerometers to provide the bed mapping, inspection repair and maintenance and defense.

sensed acceleration and rotation across six degrees of freedom. The latest models added to Advanced Navigation’s DFOG

The goal of minimizing size, weight, power and cost (SWaP-C) range are the Boreas A Series, including A90 and A70. The is driving much of the innovation underway with these systems. A Series is designed for surveying, mapping and navigation

Earlier this year, Exail released a new highly birefringent ? - across subsea, marine, land and air applications. Both of the ber for military-grade FOGs, featuring what it claims is the new models are strategic-grade inertial measurement units highest birefringence and shortest beat length available in the (IMU) that contain ultra-high accuracy DFOG and high per- industry (1mm at 633 nm). The inertial measurement unit in- formance closed-loop accelerometers. cluding ? ber coil is now less than 30mm in diameter, and the All the measurements are combined into a proprietary neural material enhancements maximize the length of ? ber that can network algorithm which removes sensor errors and ? lters out be used, thereby maximizing accuracy, whilst ensuring the interference. Advanced Navigation’s sensor fusion algorithm mechanical reliability of the coils. This ? ber is available with is more sophisticated than Kalman ? lters. Kalman ? ltering

Exail’s Phins 9

Compact weighs 1.2kg and features a power consumption of less than 7W.

Image courtesy Exail www.marinetechnologynews.com 31

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