{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,17]],"date-time":"2026-02-17T14:19:34Z","timestamp":1771337974772,"version":"3.50.1"},"reference-count":23,"publisher":"MDPI AG","issue":"24","license":[{"start":{"date-parts":[[2021,12,15]],"date-time":"2021-12-15T00:00:00Z","timestamp":1639526400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100002830","name":"Centre National d'\u00c9tudes Spatiales","doi-asserted-by":"publisher","award":["Project SAREDA_DA"],"award-info":[{"award-number":["Project SAREDA_DA"]}],"id":[{"id":"10.13039\/501100002830","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Since 2011, massive stranding of the brown algae Sargassum has regularly affected the coastal waters of the West Caribbean, Brazil and West Africa, leading to significant environmental and socio-economic impacts. The AFAI algal index (Alternative Floating Algae Index) is often used with remote sensing data in order to estimate the Sargassum coverage, and more precisely the AFAI deviation, which consists of the difference between AFAI and AFAI of the Sargassum-free background. In this study, the AFAI deviation is computed using NASA\u2019s 1 km Terra\/MODIS (Moderate-Resolution Imaging Spectroradiometer) and ESA\/Copernicus\u2019s 20 m Sentinel-2\/MSI (Multi Spectral Instrument) for the same sites and at the same time. Both MODIS and MSI AFAI deviations are compared to confirm the relevance of AFAI deviation technique for two very different spatial resolutions. A high coefficient of determination was found, thus confirming a satisfactory downsampling from 20 m (MSI) to 1 km (MODIS). Then, AFAI deviations are used to estimate the fractional coverage of Sargassum (noted FC). A new linear relationship between the MODIS AFAI deviation and FC is established using the dense Sargassum aggregations observed by MSI data. The AFAI deviation is proportional to FC with a factor of proportionality close to 0.08. Finally, it is shown that the factor is dependent on the Sargassum spectral reflectance, submersion or physiological state.<\/jats:p>","DOI":"10.3390\/rs13245106","type":"journal-article","created":{"date-parts":[[2021,12,15]],"date-time":"2021-12-15T21:47:36Z","timestamp":1639604856000},"page":"5106","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":17,"title":["Revisited Estimation of Moderate Resolution Sargassum Fractional Coverage Using Decametric Satellite Data (S2-MSI)"],"prefix":"10.3390","volume":"13","author":[{"given":"Jacques","family":"Descloitres","sequence":"first","affiliation":[{"name":"AERIS\/ICARE Data and Services Center, University of Lille, CNRS, CNES, UMS 2877, F-59000 Lille, France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2290-6383","authenticated-orcid":false,"given":"Audrey","family":"Minghelli","sequence":"additional","affiliation":[{"name":"Laboratoire d\u2019Informatique et Syst\u00e8me (LIS), Universit\u00e9 de Toulon, Aix Marseille Universit\u00e9, CNRS UMR 7020, F-83041 Toulon, France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0165-0713","authenticated-orcid":false,"given":"Fran\u00e7ois","family":"Steinmetz","sequence":"additional","affiliation":[{"name":"HYGEOS, Euratechnologies, 165 av. de Bretagne, 59000 Lille, France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Crist\u00e8le","family":"Chevalier","sequence":"additional","affiliation":[{"name":"Mediterranean Institute of Oceanography (MIO), Aix Marseille Universit\u00e9, Universit\u00e9 de Toulon, CNRS, IRD, UM 110, 13288 Marseille, France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7815-0533","authenticated-orcid":false,"given":"Malik","family":"Chami","sequence":"additional","affiliation":[{"name":"Laboratoire Atmosph\u00e8res Milieux Observations Spatiales (LATMOS), Sorbonne Universit\u00e9, CNRS-INSU, F-06304 Nice, France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5831-7399","authenticated-orcid":false,"given":"L\u00e9o","family":"Berline","sequence":"additional","affiliation":[{"name":"Mediterranean Institute of Oceanography (MIO), Aix Marseille Universit\u00e9, Universit\u00e9 de Toulon, CNRS, IRD, UM 110, 13288 Marseille, France"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,12,15]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"3619","DOI":"10.1109\/TGRS.2006.882258","article-title":"Ocean Color Satellites Show Extensive Lines of Floating Sargassum in the Gulf of Mexico","volume":"44","author":"Gower","year":"2006","journal-title":"IEEE Trans. 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