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Validation of SeaWiFS and MODIS Aqua/Terra aerosol products in coastal regions of European marginal seas

Mélin F., Zibordi G., Carlund T., Holben B. N., Stefan S.

Oceanologia

2013

No. 55 (1)

27-51

The aerosol products associated with the ocean colour missions SeaWiFS and MODIS (both Aqua and Terra) are assessed with AERONET field measurements collected in four European marginal seas for which fairly large uncertainties in ocean colour in-water products have been documented: the northern Adriatic, the Baltic, Black and North Seas. On average, more than 500 match-ups are found for each basin and satellite mission, showing an overall consistency of validation statistics across the three missions. The median absolute relative difference between satellite and field values of aerosol optical thickness ?a at 443 nm varies from 12% to 15% for the three missions at the northern Adriatic and Black Sea sites, and from 13% to 26% for the Baltic and North Sea sites. It is in the interval 16-31% for the near-infrared band. The spectral shape of ?ais well reproduced with a median bias of the Ängström exponent varying between -15% and +14%, which represents a clear improvement with respect to previous versions of the atmospheric correction scheme. These results show that the uncertainty associated with ?a in the considered coastal waters of the European marginal seas is comparable to global validation statistics.

SeaWiFS-derived products in the Baltic Sea : performance analysis of a simple atmospheric correction algorithm

Bulgarelli B., Mélin F., Zibordi G.

Oceanologia

2003

No. 45 (4)

655-677

The accuracy analysis of an approximate atmospheric correction algorithm for the processing of SeaWiFS data has been investigated for the Baltic Sea. The analysis made use of theoretical radiances produced with the FEM radiative transfer code for representative atmosphere-water test cases. The study showed uncertainties in the determination of the aerosol optical thickness at 865 nm and of the A*ngström exponent lower than š 5% and š 10%, respectively. These results were confirmed by the analysis of 59 match-ups between satellite-derived and in situ measurements for a site located in the central Baltic. Because of the relatively high yellow substance absorption, often combined with the slanted solar illumination, the retrieval of the water-leaving radiance in the blue part of the spectrum appeared to be highly degraded, to the extent that almost no correlation was found between retrieved and simulated values. Better results were obtained at the other wavelengths. The accuracy in the estimation of the remote sensing reflectance ratio R35 decreased with diminishing chlorophyll a concentration and increasing yellow substance absorption, ranging between š 7% and š 47%. The propagation of R35 uncertainties on chlorophyll a estimation was quantified. Keeping the same atmosphere-water conditions, the atmospheric correction scheme appeared sensitive to seasonal changes in the Sun zenith.