Multibeam echo sounders are the workhorse of hydrographic survey, seafloor mapping, fishery, and offshore inspection. They are also the sonar type most sensitive to vessel motion, transmitting many simultaneous beams across a wide swath where accurate attitude data is essential to position every sounding correctly in three-dimensional space.
Roll is the dominant error source for MBES. Even small roll errors translate into significant positional errors at the outer edges of the swath, particularly in deeper water where the beam geometry is more oblique. Pitch errors introduce along-track positioning errors that misalign ping returns between adjacent survey lines, producing characteristic feathering artefacts in the point cloud, while heave errors corrupt the absolute depth of every measurement.
In practice, achieving the IHO S-44 Special Order accuracy standard, required for harbour approach and docking surveys, demands roll and pitch compensation to better than 0.02° and heave compensation to better than 5 cm or 5% of depth. Without an accurate motion reference, even the most advanced multibeam system cannot deliver data that reflects its true capability.
The MRU Marine 6000 series delivers exactly the 0.02° roll and pitch accuracy required for IHO Special Order survey. For reconnaissance and general seabed mapping, the MRU Marine 3000 series at 0.05° is often sufficient, while the MRU Marine 9000 serves the most demanding high-resolution applications.
50 m depth, IP 68
5 cm or 5.0%
Lemo or SubConn 8 or SubConn 16
6000 m depth
5 cm or 5.0%
SubConn 8
"With the Norwegian Subsea MRU, our customers get a system that is easy to use, highly accurate, and doesn’t require a massive learning curve. The results speak for themselves."
"The accuracy, weight, and form factor of Norwegian Subsea MRUs are unmatched."
Ultrabeam, a specialist in hydrographic survey and underwater inspection, relies heavily on precise motion compensation to ensure accuracy in their 3D mapping projects. By integrating Norwegian Subsea’s compact, calibration-free Motion Reference Units (MRUs), Ultrabeam has significantly improved its survey data accuracy, while enjoying simplified integration, and enhanced operational efficiency in diverse surveying environments, from bridges, to offshore installations.
Motion Reference Units (MRUs) are crucial in bathymetric survey technology, providing precise motion compensation data to ensure reliable and accurate seafloor mapping. For users like Captain Sid Hynes, a seasoned mariner exploring Newfoundland’s shipwreck-rich waters, the Norwegian Subsea MRU has redefined what is possible, delivering exceptional performance even in incredibly challenging conditions.
Norwegian Subsea’s Motion Reference Units (MRUs) are now available integrated with WASSP’s multibeam sonar systems, offering enhanced motion data accuracy and performance for offshore applications.