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1

Influence of the wind field on the radiance of a marine shallow: evidence from the Caspian Sea

Karabashev G. S., Evdoshenko M. A.

Oceanologia

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2012

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No. 54 (4)

655-673

EN

The influence of the near-water wind field on the radiance of a marine shallow was studied on the basis of daily SeaWiFS ocean colour scanner data and QuickScat scatterometer wind data collected from 1999 to 2004 in the southern Caspian Sea, where the deep basin borders a vast shallow west of the shore of meridional extent. It was found that radiance distributions, clustered by wind rhumbs, exhibited different long-term mean patterns for winds of opposing directions: within the shallow's boundaries, the radiances were about twice as high for winds having an offshore component with reference to the onshore wind conditions. The zonal profile of radiance across the shallow resembled a closed loop whose upper and lower branches corresponded to the offshore and onshore winds respectively. The loop was the most pronounced at sites with 10-15 m of water for any wavelength of light, including the red region. On the basis of specific features of the study area, we attributed this pattern to sunlight backscattered from bottom sediments resuspended by bottom compensation currents induced by the offshore winds.

2

Validation of empirical and semi-analytical remote sensing algorithms for estimating absorption by Coloured Dissolved Organic Matter in the Baltic Sea from SeaWiFS and MODIS imagery

Kowalczuk P., Darecki M., Zabłocka M., Górecka I.

Oceanologia

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2010

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No. 52 (2)

171-196

EN

An extensive bio-optical data set obtained from field measurements was used to evaluate the performance of an empirical (Kowalczuk et al. 2005) and two semi-analytical algorithms: Carder et al. (1999) and GSM01 (Maritorena et al. 2002) for estimating CDOM absorption in the Baltic Sea. The data set includes coincident measurements of radiometric quantities and absorption coefficients of CDOM made during 43 cruises between 2000 and 2008. In the first stage of the analysis, the accuracy of the empirical algorithm by Kowalczuk et al. (2005) was assessed using in situ measurements of remote sensing reflectance. Validation results improved when matching points located in Gulf of Gdańsk close to the Vistula River mouth were eliminated from the data set. The calculated errors in the estimation of aCDOM(400) in the first phase of the analysis were Bias = -0.02, RMSE = 0.46 and R2 = 0.70. In the second stage, the empirical algorithm was tested on satellite data from SeaWiFS and MODIS imagery. The satellite data were corrected atmospherically with the MUMM algorithm designed for turbid coastal and inland waters and implemented in the SeaDAS software. The results of the best case scenario for estimating the CDOM absorption coefficient aCDOM(400), based on SeaWiFS data, were Bias = -0.02, RMSE = 0.23 and R2 = 0.40. The validation of the Kowalczuk et al. (2005) empirical algorithm applied to MODIS data led to a less accurate estimate of aCDOM(400): Bias = -0.03, RMSE = 0.19 and R2 = 0.29. This assessment of the accuracy of standard semi-analytical algorithms available in the SeaWiFS and MODIS imagery processing software revealed that both algorithms (GSM_01 and Carder) underestimate CDOM absorption in the Baltic Sea with mean systematic and random errors in excess of 70%. The paper presents examples of the application of the Kowalczuk et al. (2005) empirical algorithm for producing maps of the seasonal distribution of aCDOM(400) in the Baltic Sea between 2004 and 2008.

3

Algorithms for the remote sensing of the Baltic ecosystem (DESAMBEM). Part 2: Empirical validation

Darecki M., Ficek D., Krężel A., Ostrowska M., Majchrowski R., Woźniak S.B., Bradtke K., Dera J., Woźniak B.

Oceanologia

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2008

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No. 50 (4)

509-538

EN

This paper is the second of two articles on the methodology of the remote sensing of the Baltic ecosystem. In Part 1 the authors presented the set of DESAMBEM algorithms for determining the major parameters of this ecosystem on the basis of satellite data (see Woźniak et al. 2008 - this issue). That article discussed in detail the mathematical apparatus of the algorithms. Part 2 presents the effects of the practical application of the algorithms and their validation, the latter based on satellite maps of selected Baltic ecosystem parameters: the distributions of the sea surface temperature (SST), the Photosynthetically Available Radiation (PAR) at the sea surface, the surface concentrations of chlorophyll a and the total primary production of organic matter. Particular emphasis was laid on analysing the precision of estimates of these and other parameters of the Baltic ecosystem, determined by remote sensing methods. The errors in these estimates turned out to be relatively small; hence, the set of DESAMBEM algorithms should in the future be utilised as the foundation for the effective satellite monitoring of the state and functioning of the Baltic ecosystem.

4

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

Bulgarelli B., Mélin F., Zibordi G.

Oceanologia

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2003

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No. 45 (4)

655-677

EN

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.

5

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

Sikora K., Urbański J.A.

Oceanological Studies

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1999

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Vol. 28, No. 3-4

17-34

EN

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.