How Far Can We Classify Macroalgae Remotely? An Example Using a New Spectral Library of Species from the South West Atlantic (Argentine Patagonia)

Abstract

Macroalgae have attracted the interest of remote sensing as targets to study coastal marine ecosystems because of their key ecological role. The goal of this paper is to analyze a new spectral library, including 28 macroalgae from the South-West Atlantic coast, in order to assess its use in hyperspectral remote sensing. The library includes species collected in the Atlantic Patagonian coast (Argentina) with representatives of brown, red, and green algae, being 22 of the species included in a spectral library for the first time. The spectra of these main groups are described, and the intraspecific variability is also assessed, considering kelp differentiated tissues and depth range, discussing them from the point of view of their effects on spectral features. A classification and an independent component analysis using the spectral range and simulated bands of two state-of-the-art drone-borne hyperspectral sensors were performed. The results show spectral features and clusters identifying further algae taxonomic groups, showing the potential applications of this spectral library for drone-based mapping of this ecological and economical asset of our coastal marine ecosystems.

Missing the Forest and the Trees: Utility, Limits and Caveats for Drone Imaging of Coastal Marine Ecosystems

“…As spectral libraries for coastal algal species accumulate [30,[40][41][42], and as the use of finer spectral resolution imaging systems become common practice, the generation of classified products will increasingly yield greater taxonomic richness and require less validation [29]. Given the length of coastlines-in the case of New Zealand, some 11,000 km-drone-based imaging will provide a cost-effective and comprehensive quantitative assessment tool to be used in the presence of ever-increasing impacts from land-use changes [41,42], natural upheavals, and climate change.…”

“…Accurately relating remotely measured spectral signatures to in situ observations provides the key mechanism for building effective detection algorithms and assessing their accuracy [27]. Spectral libraries provide promise for remote taxonomic surveys [30], especially when aligned with low elevation hyperspectral imaging surveys [29,31], but challenges remain to deal appropriately with fundamental and realised spectra of species across seasons and under multiple scenarios of water coverage [29]. Appropriate validation of observations is also an area with no widely accepted protocols, although embedding transects has been widely used [23,26].…”

“…Once ground-truthed and calibrated, this is a transferable technology that can save hundreds of person-hours of laborious field work, obviate the continual need for identification and field specialists for long periods, and thereby give a much more spatially complete indication of recovery of the coastline. The utility of drone surveys can only increase as ground-truthing (e.g., spectral libraries, [30,[38][39][40]) improves for more species under different circumstances and different types of disturbances.…”

Assessing the Potential of Remotely-Sensed Drone Spectroscopy to Determine Live Coral Cover on Heron Reef

“…With marine public spectral libraries becoming more accessible and complete, it may be soon possible to find pure spectra with matching sensors and environmental conditions as those collected for individual studies, facilitating the pre-processing step by decreasing the need for extensive normalisation of datasets. In order to achieve this, future data collection methods should aim to standardise methods for collecting spectra for libraries and provide additional information on the factors affecting intra-specific variability, such as developmental stage, tidal position, and bathymetric position [51]. Public databases are commonly used in the fields of mineral exploration and canopy analysis, where organisation and individual researchers have combined efforts to develop shared libraries for a range of different materials, both natural and anthropogenic.…”

Classification Ensembles for Beach Cast and Drifting Vegetation Mapping with Sentinel-2 and PlanetScope

“…In the last years, remote sensing techniques have become an extensively used method for macrovegetation mapping [13,14] providing good estimates of aquatic vegetation coverage [15,16]. Moreover, remote sensing can provide long-term data to better understand ecosystem structures and changes [17].…”