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Open AccessArticle

Improving the Remote Sensing Retrieval of Phytoplankton Functional Types (PFT) Using Empirical Orthogonal Functions: A Case Study in a Coastal Upwelling Region

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Programa de Geociencias, Instituto de Investigaciones Marinas y Costeras INVEMAR, Santa Marta 470006, Colombia
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Escuela de Ciencias del Mar, Pontificia Universidad Católica de Valparaiso, Valparaiso 2340000, Chile
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Departamento de Oceanografía, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Concepción 4070386, Chile
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Instituto Milenio de Oceanografía (IMO-Chile), Concepción 4030000, Chile
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College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA
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Instituto de Oceanografía y Cambio Global, Universidad de Las Palmas de Gran Canaria, Campus Universitario de Tafira, 35017 Las Palmas de Gran Canaria, Spain
*
Author to whom correspondence should be addressed.
Remote Sens. 2018, 10(4), 498; https://doi.org/10.3390/rs10040498
Received: 12 January 2018 / Revised: 8 March 2018 / Accepted: 14 March 2018 / Published: 22 March 2018
(This article belongs to the Special Issue Remote Sensing of Ocean Colour)
An approach that improves the spectral-based PHYSAT method for identifying phytoplankton functional types (PFT) in satellite ocean-color imagery is developed and applied to one study case. This new approach, called PHYSTWO, relies on the assumption that the dominant effect of chlorophyll-a (Chl-a) in the normalized water-leaving radiance (nLw) spectrum can be effectively isolated from the signal of accessory pigment biomarkers of different PFT by using Empirical Orthogonal Function (EOF) decomposition. PHYSTWO operates in the dimensionless plane composed by the first two EOF modes generated through the decomposition of a space–nLw matrix at seven wavelengths (412, 443, 469, 488, 531, 547, and 555 nm). PFT determination is performed using orthogonal models derived from the acceptable ranges of anomalies proposed by PHYSAT but adjusted with the available regional and global data. In applying PHYSTWO to study phytoplankton community structures in the coastal upwelling system off central Chile, we find that this method increases the accuracy of PFT identification, extends the application of this tool to waters with high Chl-a concentration, and significantly decreases (~60%) the undetermined retrievals when compared with PHYSAT. The improved accuracy of PHYSTWO and its applicability for the identification of new PFT are discussed. View Full-Text
Keywords: phytoplankton functional types (PFT); ocean color; modified PHYSAT method; empirical orthogonal functions (EOF); coastal upwelling waters phytoplankton functional types (PFT); ocean color; modified PHYSAT method; empirical orthogonal functions (EOF); coastal upwelling waters
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MDPI and ACS Style

Correa-Ramirez, M.; Morales, C.E.; Letelier, R.; Anabalón, V.; Hormazabal, S. Improving the Remote Sensing Retrieval of Phytoplankton Functional Types (PFT) Using Empirical Orthogonal Functions: A Case Study in a Coastal Upwelling Region. Remote Sens. 2018, 10, 498.

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  • Supplementary File 1:

    ZIP-Document (ZIP, 3294 KB)

  • Externally hosted supplementary file 1
    Link: https://www.dropbox.com/sh/1j7sn3uo7fa60r5/AABwub8DEg1YOqsICY_PankEa?dl=0
    Description: The PHYSTWO codes are available online at www.mdpi.com/link. Content; modis_phystwo.m and modis_physat.m contain matlab codes for PHYSTWO and PHYSAT respectively; PHYSTWO_synthetic_matrix (.mat and _adjusted.mat) contain orthomodel matrices; text.m contain a demonstration script.
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