Application of Hyperspectral Imaging to Underwater Habitat Mapping, Southern Adriatic Sea

Abstract

Hyperspectral imagers enable the collection of high-resolution spectral images exploitable for the supervised classification of habitats and objects of interest (OOI). Although this is a well-established technology for the study of subaerial environments, Ecotone AS has developed an underwater hyperspectral imager (UHI) system to explore the properties of the seafloor. The aim of the project is to evaluate the potential of this instrument for mapping and monitoring benthic habitats in shallow and deep-water environments. For the first time, we tested this system at two sites in the Southern Adriatic Sea (Mediterranean Sea): the cold-water coral (CWC) habitat in the Bari Canyon and the Coralligenous habitat off Brindisi. We created a spectral library for each site, considering the different substrates and the main OOI reaching, where possible, the lower taxonomic rank. We applied the spectral angle mapper (SAM) supervised classification to map the areal extent of the Coralligenous and to recognize the major CWC habitat-formers. Despite some technical problems, the first results demonstrate the suitability of the UHI camera for habitat mapping and seabed monitoring, through the achievement of quantifiable and repeatable classifications.

Offshore Neopycnodonte Oyster Reefs in the Mediterranean Sea

“…Macro-(>2 cm) and mega-benthic organisms were identified to the lower possible taxonomic rank. Taxa unidentifiable at species level from images alone were categorized as morphological categories (e.g., [63,64]). Taxonomic classification adheres to the World Register of Marine Species database [65].…”

An Under-Ice Hyperspectral and RGB Imaging System to Capture Fine-Scale Biophysical Properties of Sea Ice

“…To the authors knowledge, only three underwater HI payload designs have been documented before. The Ecotone UHI (Ecotone, Trondheim, Norway) is a commercial solution designed for deep or shallow ROV-based seafloor observations and utilizes active light sources [36,76]. The Ecotone UHI has also been equipped onto unmanned seafloor vehicles (USV) for shallow seafloor mapping [33].…”

“…In theory, hyperspectral resolution data has the potential to resolve beyond pure biomass estimates towards more sophisticated biological traits such as ice algal photophysiology [91,97,98], species composition [97,99,100], pigment detection [101][102][103], and feature classification and mapping [35,76,104]. An interesting field is also being explored in the retrieval of primary production estimates from spectral data in combination with in-vitro photosynthetic parameters for ice algae [7,105] or with PAM fluorometry for microphytobenthic communities [106].…”

“…Low light levels will push sensors to their sensitivity limits, necessarily affect SNR and hinder the integration of pushbroom HI payloads onto more efficient and dynamic underwater platforms, such as ROVs and AUVs. A series of studies have already employed pushbroom HI sensors for seafloor mapping using ROVs [35,36,76], diver operated systems [32], or unmanned surface systems [33]. A first study has also discussed HI feasibility onto AUVs [115].…”

Underwater Hyperspectral Imaging Technology and Its Applications for Detecting and Mapping the Seafloor: A Review

“…Deep-sea ecosystems are of great significance in the study of species’ origin and evolution and geochemistry. Recently, Foglini et al [ 86 ] presented a survey on cold-water corals in the Southern Adriatic Sea at a depth of 200–700 m. By using UHI, several biological groups (such as Madrepora oculata , Desmophyllum pertusum , Desmophyllum dianthus, and large fan-shaped sponges) in this area were identified and classified. One of the classification images is shown in Figure 5 .…”