A statistical algorithm for estimating chlorophyll concentration in the New Caledonian lagoon

Guillaume Wattelez; Cécile Dupouy; Morgan Mangeas; Jérôme Lefèvre; T. Touraivane; Robert Frouin

A statistical algorithm for estimating chlorophyll concentration in the New Caledonian lagoon

Guillaume Wattelez ^{1, *} Cécile Dupouy ^{2, 3} Morgan Mangeas ⁴ Jérôme Lefèvre ⁵ T. Touraivane ¹ Robert Frouin ⁶

* Corresponding author

1 UNC - Université de la Nouvelle Calédonie

2 MIO - Institut méditerranéen d'océanologie

3 Institut de recherche pour le développement [IRD] : UMR235

4 UMR 228 Espace-Dev, Espace pour le développement

5 LEGOS NOUMEA - Laboratoire d'Etudes en Géophysique et Océanographie Spatiales

6 UC San Diego - University of California [San Diego]

Abstract : Spatial and temporal dynamics of phytoplankton biomass and water turbidity can provide crucial information about the function, health and vulnerability of lagoon ecosystems (coral reefs, sea grasses, etc.). A statistical algorithm is proposed to estimate chlorophyll-a concentration ([chl-a]) in optically complex waters of the New Caledonian lagoon from MODIS-derived " remote-sensing " reflectance (R rs). The algorithm is developed via supervised learning on match-ups gathered from 2002 to 2010. The best performance is obtained by combining two models, selected according to the ratio of R rs in spectral bands centered on 488 and 555 nm: a log-linear model for low [chl-a] (AFLC) and a support vector machine (SVM) model or a classic model (OC3) for high [chl-a]. The log-linear model is developed based on SVM regression analysis. This approach outperforms the classical OC3 approach, especially in shallow waters, with a root mean squared error 30% lower. The proposed algorithm enables more accurate assessments of [chl-a] and its variability in this typical oligo-to meso-trophic tropical lagoon, from shallow coastal waters and nearby reefs to deeper waters and in the open ocean.

Keywords : chlorophyll-a concentration MODerate resolution Imaging Spectroradiometer (MODIS) ocean color remote sensing statistical algorithm oligotrophic waters New Caledonia coral lagoon

Document type :

Journal articles

Domain :

Sciences of the Universe [physics] / Ocean, Atmosphere

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