Retrieving aerosol characteristics and sea-surface chlorophyll from satellite ocean color multi-spectral sensors using a neural-variational method

• Published in: Remote sensing of environment Vol. 130; pp. 74 - 86
• Main Authors: Diouf, D., Niang, A., Brajard, J., Crepon, M., Thiria, S.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 15.03.2013; Elsevier
• Subjects: Aerosols; Animal, plant and microbial ecology; Applied geophysics; Biological and medical sciences; Dusts; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; Geophysics; Internal geophysics; NeuroVaria; Ocean color; Physics; Remote sensing; SeaWiFS; Self-organizing maps; Teledetection and vegetation maps; West Africa; Atlantic Ocean; Africa; SeaWiFS; Dusts; Self-organizing maps; NeuroVaria; Aerosols; Ocean color; Remote sensing; atmosphere; Initialization; algorithms; spectra; Sea surface; color; aerosols; Classifier; Image; 2009; 1997; dust; satellites; Multispectral detection; concentration; Method; classification; monitoring; Chlorophyll a; Type; marine environment; Characteristics; Parameter; Pixel
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2012.11.002

We developed a two-step algorithm for retrieving and then monitoring the concentration of Saharan dusts and of the sea-surface chlorophyll from satellite ocean-color multi-spectral observations. The first step consisted in classifying the top of the atmosphere (TOA) spectra using a neuronal classifier, which provided the aerosol type and a first-guess value of the aerosol parameters that was used to initialize the variational method. The variational method was the second step, which retrieved accurate measurements of the aerosol and chlorophyll-a concentrations. The algorithm was conditioned to take into account the absorbing aerosols, such as the Saharan dusts. We used this algorithm to analyze 13years of SeaWiFS images (September 1997–December 2009) over an area of the Atlantic Ocean off the coast of West Africa. Since our method allowed us to take Saharan dusts into account, the number of pixels processed for retrieving the chlorophyll-a concentration was an order of magnitude higher than that processed by the standard SeaWiFS algorithm. The analysis of the SeaWiFS images showed that the Saharan dust concentration was maximal in summer during the rainy season and minimal in autumn, which could be explained by the seasonal variability of dust emission triggered by mesoscale atmospheric processes (low-level jet and convection) and soil characteristics (humidity and vegetation). ► An algorithm was proposed to retrieve aerosol/oceanic properties from satellite data. ► The algorithm, named SOM-NV, was applied off the west African coast. ► SOM-NV provides new product and accurate aerosol optical thickness (AOT). ► It was found that the Saharan dust was at maximum in summer and minimum in November. ► A 13year climatology of aerosol type, AOT and chl-a concentration is available.