Estimation of chlorophyll-a concentration in waters over the continental shelf of the Bay of Biscay: a comparison of remote sensing algorithms
Résumé
Ocean colour imagery is used increasingly as a tool to assess water quality via chlorophyll-a concentration estimations in European waters. The Bay of Biscay is affected by major river discharges, which alter the constituents of the marine waters. Chlorophyll-a algorithms, designed for use at global scales, are less accurate due to the variability of optically-active in- water constituents. Hence, regionally-parameterized empirical algorithms are necessary. The main objective of the present study was to develop a regional algorithm to retrieve chlorophyll-a concentration (Chla) in surface water using in-situ Remote Sensing Reflectance (Rrs), for a subsequent application to MERIS satellite images. To address this objective, a platform was developed initially and a measurement procedure adapted for the field HR4000CG Spectrometer. Subsequently, the procedure was tested during a survey over the southeastern Bay of Biscay (North-East Atlantic Ocean), to establish a MERIS Chla algorithm for the area, by comparing different global remote sensing Chla algorithms, with band ratios. Results validated with the jackknife resampling procedure show a satisfactory relationship between the 510/560 nm Rrs ratio (r2jac = 0.681). This ratio is better correlated to Chla than those obtained with established Chla remote sensing algorithms. High content in coloured dissolved organic matter (CDOM>0.4 m-1) and suspended particulate matter (SPM>2.8 mg.l-1) influenced this relationship, with yellow substances having a stronger effect.
Domaines
Sciences de l'ingénieur [physics]
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