Experimental Investigation of Non-contact 3D Sensors for Marine-growth Cleaning Operations

Marine growth on submerged structures causes additional mechanical loads from drag and mass increases. In order to ensure structural integrity, regular inspection and cleaning procedures are carried out on the submerged structures, most commonly using remote-operated vehicles (ROVs). Often, the measurement methodology in these inspections is spot-checks using simple mechanical gauges, which yield a rough estimate of marine growth thickness. Expanding on this method, in order to optimize these inspection and cleaning procedures, modern methods for 3D surface measurement can be applied to increase inspection quality and ensure that superfluous cleaning is not carried out. This work investigates three state-of-the-art sensor technologies: a Time-of-Flight depth camera based on modulated visible blue laser illumination, a commercial stereo-vision solution based on visible-light sensors, and high-frequency imaging sonar. The sensors' performance has been compared in a laboratory environment to assess their suitability for use as a measurement device for marine-growth measurement in terms of accuracy, resolution, and noise/artifacts. It is concluded that the measurement fidelity of all evaluated sensors shows promise for the application, pending future evaluation in a real-world test.