Three-dimensional measurement of underwater work sites using structured laser light

Abstract

Some current operations with remotely operated vehicle (ROVs) require the vehicle to fix itself onto an underwater work site and carry out robotic tasks. For this to occur, a real-time computer model of the work site and its relationship to the vehicle must be determined, especially if the work site has not been designed for such interventions and no fixed docking structure is available. We described a laser-based system that can be used from an ROV to scan the underwater work site and translate the information into a CAD or virtual reality (VR) model. A single stripe is projected onto the work site and an image acquired by the ROV. An image-processing routine is used to optimize object range and shape information obtainable from this stripe and, when several such stripe positions have been determined, the information is combined. This paper concentrates on the image-processing techniques needed to isolate information from underwater images and the results obtained in trials of the system in a laboratory tank. The methodology is able to accommodate differing turbidities and the limitations of the system in terms of accuracy are discussed.

Generation of High‐resolution Three‐dimensional Reconstructions of the Seafloor in Color using a Single Camera and Structured Light

“…However, these methods suffer from difficulties of matching features in turbid water (Garcia & Gracias, 2011) and over terrain with few visual features, and they lead to variable resolution across the map as a function of the abundance of visual clues. Techniques for mapping bathymetry with consistently high resolution include different types of structured light by employing scanning point lasers (Kocak, Caimi, Das, & Karson, 1999;Moore, Jaffe, & Ochoa, 2000), line lasers (Inglis et al, 2012;Kondo et al, 2004;Tetlow & Spours, 1999), or light pattern projections (Bruno et al, 2011), which make use of the known relative positions of the camera and the projector. Measurements of the time of flight of a light impulse are used in LIDAR (Light Detection and Ranging) (Harsdorf et al, 1999) and serial imaging systems (Dalgleish et al, 2013).…”

Experimentation of structured light and stereo vision for underwater 3D reconstruction

“…As an example, the system could be fixed on a frame placed on the seabed for the relief of small objects in archaeological sites or in the study of the growth of coral reefs, where a very high precision is required. Another possible application could be in pipeline inspections (Rives and Borrelly, 1997;Tetlow and Spours, 1999) where a ROV may anchor the scanner to the pipeline (as previously done for gamma ray imaging (Roche et al, 2006)). …”

“…spotlights, lamps) just to ensure an efficient lighting of the scene (Allais et al, 2007), while structured light sources (i.e. lasers), used by active systems, allow imaging at greater ranges and higher contrast reducing the backscattering (Tetlow and Spours, 1999). On the other hand, passive systems (i.e.…”

A pipeline for structured light bathymetric mapping

“…Underwater vehicles are typically used to produce these data products with down looking stereo cameras and high frequency multibeam sonars. More recently, several varieties of structured light systems, including point [1], line [2] and fullfield [3] have been developed for bathymetric reconstruction. These techniques have successfully been applied to archaeology [3], [4], geo-acoustics [5] and other geomorphological applications [6].…”