Page 53: of Marine Technology Magazine (March 2025)

ing in real time, ensuring that the sonar returns are accurately positioned relative to the seabed.

RTK positioning is an established method for precise exter- nal corrections including heave, using land-based stations to re? ne accuracy to within a few centimeters. However, RTK is limited to nearshore environments, and requires base station ownership, or subscription services. This means that offshore users, particularly those conducting surveys in deeper waters, often struggle to obtain the necessary heave data accuracy without incurring signi? cant costs.

The challenge is further compounded, as other MRUs capa- ble of providing the level of motion compensation that a mul- tibeam survey requires, can be prohibitively expensive. These top-end motion sensors offer exceptional heave accuracy, but their price tag places them out of reach for many operators.

Norwegian Subsea’s MRU technology platform was designed to bridge this gap, delivering comparable accuracy at less

Courtesy Captain Sid Hynes than half the cost, while requiring no external infrastructure for maximum height data accuracy. For surveyors and com- mercial mariners looking to maintain precise data collection without the constraints of adding RTK services or the most costly motion sensors, this represents a substantial opportunity to improve data quality.

A New Motion Compensation Alogrithm

Norwegian Subsea MRUs are able to offer such high per- formance while reducing costs at the same time thanks to the company’s proprietary algorithm. The motion sensor algorithm adapts automatically to give optimized performance for the given sea condition. By using motion constraints for ? oating vessels, it can accurately compensate for residual sensor errors such as gyroscope and accelerometer bias and estimate the lo- cal gravity. The algorithms are also robust to horizontal accel- erations and will output accurate roll and pitch even under dif? - cult conditions with sideways motion. This is key to delivering accurate and robust motion measurements for any condition.

The superior heave compensation offered by Norwegian Sub-

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