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Article

Automatic Detection of Optical Signatures within and around Floating Tonga-Fiji Pumice Rafts Using MODIS, VIIRS, and OLCI Satellite Sensors

1
Aix Marseille Université, Université de Toulon, IRD, CNRS/INSU, Observatoire des Sciences de l’Univers Pythéas, UM 110, Mediterranean Institute of Oceanography (MIO), CEDEX 09, 13288 Marseille, France
2
Pacific Centre for Environment and Sustainable Development (PaCE-SD), The University of the South Pacific, Laucala Campus, Suva, Fiji
3
Scripps Institution of Oceanography, University of California San Diego, 8810 Shellback Way, La Jolla, CA 92093, USA
4
ENTROPIE, Centre IRD de Nouméa, BP A5, 98848 Nouméa, New Caledonia
*
Author to whom correspondence should be addressed.
Academic Editor: Malgorzata Stramska
Remote Sens. 2021, 13(3), 501; https://doi.org/10.3390/rs13030501
Received: 31 December 2020 / Revised: 27 January 2021 / Accepted: 27 January 2021 / Published: 31 January 2021
(This article belongs to the Special Issue Atmospheric Correction for Remotely Sensed Ocean Color Data)
An underwater volcanic eruption off the Vava’u island group in Tonga on 7 August 2019 resulted in the creation of floating pumice on the ocean’s surface extending over an area of 150 km2. The pumice’s far-reaching effects from its origin in the Tonga region to Fiji and the methods of automatic detection using satellite imagery are described, making it possible to track the westward drift of the pumice raft over 43 days. Level 2 Moderate Resolution Imaging Spectroradiometer (MODIS), Visible Infrared Imaging Radiometer Suite (VIIRS), Sentinel-3 Ocean and Land Color Instrument (OLCI), and Sentinel-3 Sea and Land Surface Temperature Radiometer (SLSTR) imagery of sea surface temperature, chlorophyll-a concentration, quasi-surface (i.e., Rayleigh-corrected) reflectance, and remote sensing reflectance were used to distinguish consolidated and fragmented rafts as well as discolored and mesotrophic waters. The rafts were detected by a 1 to 3.5 °C enhancement in the MODIS-derived “sea surface temperature” due to the emissivity difference of the raft material. Large plumes of discolored waters, characterized by higher satellite reflectance/backscattering of particles in the blue than surrounding waters (and corresponding to either submersed pumice or associated white minerals), were associated with the rafts. The discolored waters had relatively lower chlorophyll-a concentration, but this was artificial, resulting from the higher blue/red reflectance ratio caused by the reflective pumice particles. Mesotrophic waters were scarce in the region of the pumice rafts, presumably due to the absence of phytoplanktonic response to a silicium-rich pumice environment in these tropical oligotrophic environments. As beach accumulations around Pacific islands surrounded by coral shoals are a recurrent phenomenon that finds its origin far east in the ocean along the Tongan trench, monitoring the events from space, as demonstrated for the 7 August 2019 eruption, might help mitigate their potential economic impacts. View Full-Text
Keywords: ocean color; remote sensing; Tonga-Fiji; pumice rafts; chlorophyll-a ocean color; remote sensing; Tonga-Fiji; pumice rafts; chlorophyll-a
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MDPI and ACS Style

Whiteside, A.; Dupouy, C.; Singh, A.; Frouin, R.; Menkes, C.; Lefèvre, J. Automatic Detection of Optical Signatures within and around Floating Tonga-Fiji Pumice Rafts Using MODIS, VIIRS, and OLCI Satellite Sensors. Remote Sens. 2021, 13, 501. https://doi.org/10.3390/rs13030501

AMA Style

Whiteside A, Dupouy C, Singh A, Frouin R, Menkes C, Lefèvre J. Automatic Detection of Optical Signatures within and around Floating Tonga-Fiji Pumice Rafts Using MODIS, VIIRS, and OLCI Satellite Sensors. Remote Sensing. 2021; 13(3):501. https://doi.org/10.3390/rs13030501

Chicago/Turabian Style

Whiteside, Andra, Cécile Dupouy, Awnesh Singh, Robert Frouin, Christophe Menkes, and Jerome Lefèvre. 2021. "Automatic Detection of Optical Signatures within and around Floating Tonga-Fiji Pumice Rafts Using MODIS, VIIRS, and OLCI Satellite Sensors" Remote Sensing 13, no. 3: 501. https://doi.org/10.3390/rs13030501

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