In a short period of time, subsea laser scanning has sprung up as a new viable option for subsea imaging and measurement. Elaine Maslin takes a look.
Buoyancy collar. Images from 2G Robotics.
A number of firms appeared, around the late 2000s, offering subsea laser scanning technologies, already used topside, including Cathx (OE: August 2015) and 2G Robotics.
The attraction of laser scanning is that it can offer greater detail – mm-level detail – point clouds, from which detailed measurements can be taken, of subsea structures or equipment, and assessment of asset integrity issues, such as corrosion or other damage.
The technology works by using the “time of flight” principle or triangulation-scanning techniques. The results can be turned into images in real time, on dynamic surveys, and exported to CAD packages.
Because it’s using optical light, while it struggles to see through silt, for example, it is more accurate than sonar, by a level of magnitude, as sound waves attenuate in the water.
Jason Gillham, founder and CEO of Canadian measurement solutions firm 2G Robotics, started to look into subsea laser technologies in 2008, when a project they were working on, relating to requirements for a near-range, high-precision localization and mapping sensor for underwater robotics, needed this type of technology.
“There was nothing commercially available so we started developing our own,” he says. “Acoustics is the most prevalent and most common technology used for mapping. But it didn’t have the level of detail we were looking for. By 2010, we had developed our own technology.”
A wellhead connector, shown from data a subsea laser scan.
To date the firm’s ULS-500 laser has performed more than 2500km of pipeline and seabed scanning from AUVs, traveling at 4+ knots, and survey and work class ROVs worldwide. One was also used to scan the hull of the ill-fated Italian cruise ship, Costa Concordia, in 2013.
2G Robotics’ system works by sending a laser line to the target surface. An optical sensor (which moves to collect 3D data) then captures the return signals, which are then calculated into a 3D point cloud. 2G has developed the system so this can be carried out from a moving object (ROV/AUV etc.) with the imaging processed real-time. This has proved an interesting prospect for firms wishing to perform pipeline scans. Post processing can also be performed for further assessment work.
Pipeline damage and free span assessment are two of the more popular areas for use of the tool, he says, alongside anode assessment. Subsea metrology is also a key area, where an operator or contractor wants increased dimension certainty. “With the current downturn, there’s a real benefit from the efficiency stand point, from dynamic surveys,” he says, “to quickly capture details you cannot get traditionally.”
But there’s still a place for sonar, Gillham adds. “Laser scanners aren’t for finding something new [an object for example], it’s great for measuring something you have already found.” Sonar is the tool for finding the object in the first place.