Challenges of close-range underwater optical mapping

Abstract

Abstract-Underwater optical mapping often involves the use of image mosaicing techniques. High quality mosaicing requires the application of blending methods to achieve continuous and artifact-free mosaics. Image blending has a dilated history of over three decades in the terrestrial and aerial fields. Unfortunately, the nature of the underwater medium adds additional difficulties to the mosaicing and blending tasks. In this paper a survey of the blending methods is given, focusing the attention on its applicability to underwater mosaicing. Image acquisition is performed by Autonomous Underwater Vehicles (AUVs) or Remotely Operated Vehicles (ROVs) in the deep ocean, a medium with aggressive light absorption and disrupting scattering effects that requires of the use of artificial lighting. A comprehensive comparison of the basic features and limitations of some of the most important existing blending techniques is presented. The goal is the generation of seamless and visually pleasant large area photo-mosaics of the seafloor, free from double contouring, ghosting and other disturbing and common blending artifacts.

Structure, temporal evolution, and heat flux estimates from the Lucky Strike deep‐sea hydrothermal field derived from seafloor image mosaics

“…In all surveys, image acquisition was synchronized with strobe lights. The mosaic‐building procedure is briefly summarized here and a full description and technical details are available elsewhere [ Prados et al , 2011]. First, acquired raw images are pre‐processed to a) correct for uneven illumination from the lighting system and imaging geometry, b) equalize overall intensity among images, and c) correct the optical geometric distortion due to the camera lenses.…”

“…Image blending techniques are then applied to the mosaic to remove image edges and other mosaicing artifacts, and to insure that higher resolution imagery acquired closer to the seafloor is retained preferentially in areas with overlapping frames. This processing renders a seamless, single mosaic image [ Prados et al , 2011], with ∼230,000 × 150,000 pixels at a resolution of 5 to 10 mm for the Lucky Strike data set (Table 1). Available near‐bottom multibeam bathymetry (Momareto'06 cruise [ Ondréas et al , 2009]), which has a nominal horizontal resolution of 0.4 m and 1.5 m, provides information on seafloor morphology and tectonic structures (i.e., faults) that may be associated with hydrothermal discharge.…”

“…However, all these more recent surveys are limited to a small surface area (e.g., 10,000 m 2 [ Maki et al , 2008]), and thus not well adapted to map a complete hydrothermal field such as that of Lucky Strike. In recent years, we have developed new image‐processing techniques [ Escartín et al , 2008a; Garcia et al , 2011; Prados et al , 2011] tailored to map large areas of up to 1 km 2 or more, thus expanding the possible applications for seafloor image surveying and their quantitative interpretation.…”

Robustly Removing Deep Sea Lighting Effects for Visual Mapping of Abyssal Plains

“…Once enhanced or restored versions of the original images have been created, usually some water or lighting effects remain. In order to create large maps, different mosaicing and blending strategies can be applied (see [36] for a discussion). Note however that the main goal of blending strategies is to make artefacts less prominent (e.g.…”

Graph theory approach for match reduction in image mosaicing

“…The short-range nature of image acquisition causes inaccuracies in image registration [13]. These result in misalignments when images are mapped onto a common frame (usually referred to as the mosaic or the global frame).…”