Abstract
Underwater inspection, maintenance and repair (IMR) operations are being increasingly robotized in order to reduce safety issues and costs. These robotic systems rely on vision sensors to perform fundamental tasks, such as navigation and object recognition and manipulation. Especially, active optical 3D scanners are commonly used due to the domain-specific challenges of underwater imaging. This paper presents an exhaustive survey on the state of the art of optical 3D underwater scanners. A literature review on light projection and light-sensing technologies is presented. Moreover, quantitative performance comparisons of underwater 3D scanners present in the literature and commercial products are carried out.
Highlights
Oceans cover 71% of the Earth’s surface, of which 95% is still unexplored [1]
silicon photomultipliers (SiPMs) are composed of multiple single-photon avalanche photodiodes (SPADs), which are APDs in Geiger mode aimed at detecting single photons [83]
The depth resolution of a ToF scanner depends on the resolution of the time or phase measurement but not on the scan distance, unlike for triangulation scanners. This fact was studied by McLeod et al [96], who identified a threshold of ranges (
Summary
Oceans cover 71% of the Earth’s surface, of which 95% is still unexplored [1]. Oceanic exploration is a growing field but diving deeper than 50 m poses a huge challenge to human divers. The main advantages of passive sensors such as passive stereo systems [22,25] and photometric stereo [26,27] are their low price and their theoretical high lateral resolution, which is mainly limited by forward-scattered light [28] (see Figure 1) Their main drawbacks are that they are computationally demanding and rely heavily on the target’s texture to extract features from the image. The present survey reviews the state of the art of active underwater 3D optical sensors, focusing especially on the technologies for light projection and light sensing. Their working principles, as well as their practical limitations, are explained.
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