Wyniki wyszukiwania - Biblioteka Nauki

1

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

100%

Bulgarelli B. , Mélin F. , Zibordi G.

Oceanologia

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2003

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tom 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.

2

Spectral effects in bio-optical control on the ocean system

100%

Sathyendranath S. , Platt T.

Oceanologia

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2007

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tom 49

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nr 1

EN

The influence of phytoplankton on the spectral structure of the submarine irradiance field is reviewed. The implications for the ocean system of the spectral response by phytoplankton to the ambient light field are discussed. For example, it provides the basis for retrieval of phytoplankton biomass by visible spectral radiometry (ocean-colour remote sensing). In the computation of primary production, the results of spectral models differ in a known and systematic manner from those of non-spectral ones. The bias can be corrected without risk of incurring additional random errors. The models in use for phytoplankton growth, whether based on available light or absorbed light, whether expressed in terms of chlorophyll or carbon, are shown all to conform to the same basic formalism with the same parameters. Residual uncertainty lies less with the models than with the parameters required for their implementation. The submarine light field and the spectral characteristics of phytoplankton carry latent information on phytoplankton community structure. Differences in spectral response by different functional types of phytoplankton are small but significant. Optical considerations limit the maximum phytoplankton biomass that can be sustained in a given surface mixed layer. Moreover, the upper bound on the biomass depends on the spectral response of the dominant phytoplankton taxa. As a result, an optical control exists in the mixed layer that tends to resist extreme excursions of the biomass and also to maintain biodiversity in the phytoplankton.

3

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

67%

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

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nr 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

Diffusive component of the vertical flux of particulate organic carbon in the North polar Atlantic

67%

Stramska M.

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nr 4

EN

The diffusive component of the vertical flux of particulate organic carbon (POC) from the surface ocean layer has been estimated using a combination of the mixed layer model and ocean color data from the SeaWiFS satellite. The calculations were carried out for an example location in the north polar Atlantic centered at 75◦N and 0◦ E for the time period of 1998–2004. The satellite estimates of surface POC derived using a regional ocean color algorithm were applied as an input to the model driven by local surface heat and momentum fluxes. For each year of the examined period, the diffusive POC flux was estimated at 200-m depth from April through December. The highest flux is generally observed in the late fall as a result of increased heat loss and convectional mixing of surface waters. A relatively high diffusive POC flux is also observed in early spring, when surface waters are weakly stratified. In addition, the model results demonstrate significant interannual variability. The highest diffusive POC flux occurred in 1999 (about 4500 mg m−2 over the 9-month period). In 1998 and 2002 the estimated flux was about two orders of magnitude lower. The interannual variability of the diffusive POC flux is associated with mixed layer dynamics and underscores the importance of atmospheric forcing for POC export from the surface layer to the ocean’s interior.