Underwater Hyperspectral Imaging (UHI): A Review of Systems and Applications for Proximal Seafloor Ecosystem Studies

Abstract

Marine ecosystem monitoring requires observations of its attributes at different spatial and temporal scales that traditional sampling methods (e.g., RGB imaging, sediment cores) struggle to efficiently provide. Proximal optical sensing methods can fill this observational gap by providing observations of, and tracking changes in, the functional features of marine ecosystems non-invasively. Underwater hyperspectral imaging (UHI) employed in proximity to the seafloor has shown a further potential to monitor pigmentation in benthic and sympagic phototrophic organisms at small spatial scales (mm–cm) and for the identification of minerals and taxa through their finely resolved spectral signatures. Despite the increasing number of studies applying UHI, a review of its applications, capabilities, and challenges for seafloor ecosystem research is overdue. In this review, we first detail how the limited band availability inherent to standard underwater cameras has led to a data analysis “bottleneck” in seafloor ecosystem research, in part due to the widespread implementation of underwater imaging platforms (e.g., remotely operated vehicles, time-lapse stations, towed cameras) that can acquire large image datasets. We discuss how hyperspectral technology brings unique opportunities to address the known limitations of RGB cameras for surveying marine environments. The review concludes by comparing how different studies harness the capacities of hyperspectral imaging, the types of methods required to validate observations, and the current challenges for accurate and replicable UHI research.

Remote Sensing of the Tautra Ridge: An Overview of the World’s Shallowest Cold-Water Coral Reefs

“…To provide spatially coherent hyperspectral imagery, UHI-4 must therefore be maneuvered in straight lines across the given area of interest, with the light entrance slit of the hyperspectral camera oriented perpendicularly to the instrument platform's heading. Over the past decade, UHI-based seafloor studies have been carried out within a variety of fields (e.g., marine biology and archaeology), and for an overview of the technique, see Liu et al (2020) and Montes-Herrera et al (2021).…”

Underwater Hyperspectral Imaging of Arctic Macroalgal Habitats during the Polar Night Using a Novel Mini-ROV-UHI Portable System

“…The use of underwater hyperspectral imaging (UHI) was first published in 2013 [1,2] and first reviewed by [3,4], covering the use of UHI for the identification and mapping of different bio-geo-chemical Objects of Interest (OOI). UHI has been conducted from different instrument-carrying platforms, such as SCUBA diving [2,5] landers [6], underwater slides [1], remotely operated vehicles (ROV) operating from the surface and down to 4200 m [5,[7][8][9][10], autonomous underwater vehicles (AUV) [11] and unmanned surface vehicles (USV), [12].…”

“…Fast, precise, and affordable approaches for the identification, mapping and monitoring of marine habitats are needed to provide knowledge and information for nature management and policy-making decisions in marine environments [7]. In situ sampling and mapping of seabed natural communities involving divers, ship-based acoustics, box corers, trawls, RGB photography and video are usually spectrally limited [4]. Satellitebased ocean colour techniques only cover surface waters, while information from the deep habitats is missing.…”

Exploring time series of hyperspectral images for cold water coral stress response analysis

“…Underwater hyperspectral imagers (UHI) for recording HSI have been implemented on underwater vehicles in situ for mapping extent and distribution of habitats [ 14 , 15 ] such as deep-water corals and coralligenous habitats [ 16 ], red calcareous algae and associated fauna [ 17 ] or deep sea megafauna [ 18 ]. In recent years, few multivariate image analysis applications [ 19 ] have shown that objects of interest can be identified based on their spectral signatures [ 20 , 21 ].…”