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Evaluating the extent of the River Wisła freshwater plume in the Gulf of Gdańsk using seaWiFS data

100%

Sikora K. , Urbański J. A.

tom Vol. 28, No. 3-4

17-34

The extent of the River Wisla (Vistula) water plume in the Gulf of Gdansk was investigated using SeaWiFS (Sea-viewing Wide Field-of-view Sensor) data as the basis for PCA (Principal Components Analysis), indexation, composite and classic methods of classification (i.e. maximum likelihood classification and fuzzy sets). The percentage transformation of this data is suggested in order to obtain a high relative diversity of remotely sensed signals emerging from optically different waters. Comparison of the results obtained using these different classification methods showed that PCA was especially useful in this respect.

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

86%

Bulgarelli B. , Mélin F. , Zibordi G.

tom 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.