Abstract
Coral reefs are an essential source of marine biodiversity, but they are declining at an alarming rate under the combined effects of global change and human pressure. A precise mapping of coral reef habitat with high spatial and time resolutions has become a necessary step for monitoring their health and evolution. This mapping can be achieved remotely thanks to satellite imagery coupled with machine-learning algorithms. In this paper, we review the different satellites used in recent literature, as well as the most common and efficient machine-learning methods. To account for the recent explosion of published research on coral reel mapping, we especially focus on the papers published between 2018 and 2020. Our review study indicates that object-based methods provide more accurate results than pixel-based ones, and that the most accurate methods are Support Vector Machine and Random Forest. We emphasize that the satellites with the highest spatial resolution provide the best images for benthic habitat mapping. We also highlight that preprocessing steps (water column correction, sunglint removal, etc.) and additional inputs (bathymetry data, aerial photographs, etc.) can significantly improve the mapping accuracy.
Highlights
To the best of our knowledge, even though we found some papers using contextual editing for bathymetry studies, it has not been applied to coral reef mapping in the past 10 years
Through all the papers studying coral reefs between 2018 and 2020 and mapping them from satellite imagery, the best results are obtained with Random Forest (RF) and SVM methods, even though the achieved overall accuracy almost never reaches 90%, and is often below
When performing coral mapping from satellite images, it is very common to apply a wide range of preprocessing
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland.Attribution (CC BY) license (https://creativecommons.org/licenses/by/ 4.0/).Coral reefs are complex ecosystems, home to many interdependent species [1] whose roles and interactions in the reef functioning are still not fully understood [2]. By the end of the 20th century, reefs were estimated to cover a global area of 255,000 km2 [3], which is roughly the size of the United Kingdom. Although this number represents less than 0.01%
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