Fraser Dalgleish

This article describes a compact full-waveform pulsed laser line scanner (PLLS-360°) mountable on small autonomous underwater vehicles (AUVs). The PLLS-360° is an omnidirectional imager suitable for applications, such as seafloor mapping, underwater asset inspection, object detection, ice-sheet mapping, and construction progress monitoring due to its 360° field of view (FOV). This article provides an overview of the PLLS-360°. It further discusses the system’s performance and describes how the data for this unique 360° FOV architecture is processed. The processing of the measurements involves correcting for the system receiver characteristics, geometric spreading of the returned signals, light attenuation in water, and the AUV’s motion and position to enhance the visualization of underwater 3-D scenes. This article further highlights some of the applications of the LiDAR system in ocean mapping.

It has been shown by experiment that the vision sensor as detailed in this chapter, whilst simultaneously acquiring bathymetry and reflectivity profiles, can derive robust altitude data at extended ranges (4-8 m) over extended image sequences using laser tπangulation alone to an accuracy of between 1 and 5 per cent. In addition, it is possible to utilize the unused portion of the CCD image to determine horizon tal motion by means of a region-based tracker. The combined measurements from the region-based tracker and the laser triangulation sensor can produce a stand-alone accuracy of around 97 per cent of the distance travelled at an altitude of 4 m in filtered seawater. This result is subject to degradation as the turbidity of the water increases, the velocity and altitude increase and the planar nature of the tank bottom is reduced. Finally, as well as deriving navigational information, the motion detected can be used to modify contrast enhanced composite waterfall images such that they are spatially representative of the actual seabed scene.