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Narrowband shortwave minima of multispectral reflectance as indication of algal blooms associated with the mesoscale variability in the Brazil-Malvinas Confluence

Karabashev G. S., Evdoshenko M. A.

Oceanologia

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2018

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No. 60 (4)

527--543

EN

We examine the narrowband shortwave minima (NSM) of multispectral reflectance as indication of mesoscale algal blooms. They are frequent in the Brazil-Malvinas confluence zone (BMCZ) where our testing site (TS) belongs. Its MODIS A images of December 2008 and 2014 were the source of initial data. Classification of reflectance spectra in these images revealed that the TS look from space was determined by the most populated cluster of pixels having the only NSM at 443 nm. We divided this cluster into sub-clusters by maximum wavelengths λmax from 412 to 555 nm and retrieved the estimates of λmax (proxy for abundance of colored dissolved organic matter (CDOM)), chl_a (MODIS chlorophyll), Rrs (555) (turbidity proxy), and CALH (NSM-based chlorophyll) on a pixel-by-pixel basis. This allowed us to demonstrate: (1) the NSM magnitude at 443 nm peaked in mesoscale structures, (2) CALH was consistent with chlorophyll in the BMCZ waters samples, (3) positive linear correlation of Rrs (555) and CALH was characteristic of the TS waters at any λmax, (4) the MODIS chl_a was overestimated when λmax > 488 nm, (5) localization and outlines of mesoscale structures agreed well in the fields of pairs Rrs (555) – CALH and λmax – chl_a, but not in the CALH – chl_a pair. The NSM-based chlorophyll CALH outperformed the standard chl_a determinations in exactness because the CALH is insensitive to CDOM. This is advantageous when studying the Case 1 waters of intensive mesoscale variability where chlorophyll co-exists with the CDOM from eddy-induced blooms.

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Narrowband shortwave minima in spectra of backscattered light from the sea obtained from ocean color scanners as a remote indication of algal blooms

Karabashev G. S., Evdoshenko M. A.

Oceanologia

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2016

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No. 58 (4)

279--291

EN

We propose a new approach to indication of algal blooms. It stems from analysis of the multispectral satellite reflectance Rrs of areas where blooms were documented during recent decades. We found that spectra of algal blooms exhibit minima at wavelengths of channels of Moderate Resolution Imaging Spectroradiometer (MODIS) λ = 443 and λ = 488 nm (Baltic, Black, and Caspian seas), λ = 443 nm (Southwest Tropical Pacific (SWTP)), and λ = 443 nm and λ = 469 nm (Patagonian Continental Shelf (PCS)), attributable to absorption bands of chlorophyll a and accessory pigments. We quantified the minima using indices D1 = Rrs(443) − Rrs (412) and D2 = Rrs (488) − Rrs (469) and proved their diagnostic potential by comparing their distributions to that of Rrs (555). Linear dependence of D1 upon chlorophyll a was found from MODIS data for the bloom of Nodularia spumigena. Time dependences of D1 and D2 point to the latter as a probable remote forerunner of cyanobacterial blooms. In the PCS, D1 and D2 proved to be too simplistic owing to diversity of spectral shapes at λ < 550 nm. Cluster analysis revealed close linkage of the latter and local oceanological conditions. Our findings bear witness to the diagnostic potential of the indices by virtue of their direct relation to pigment absorption and because the broadband background reflectance changes reduce when calculating the indices as a difference of spectrally close reflectances. Further studies are needed to convert the indices to band-difference algorithms for retrieving the bio-optical characteristics of algal blooms.

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Optical properties of the one-dimensional organic conductors ß-(EDT-TTF-I2)2(Pb5/6 1/6I2)3 and ß-(EDT-TTF-I2)2(Pb2/3+xAg1/3-2x xI2)3, x = 0.05

Olejniczak I., Gromadziński B., Graja A., Devic T., Batail P.

Materials Science Poland

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2004

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Vol. 22, No. 4

347--352

EN

We report the room-temperature polarized infrared reflectance spectra of two radical cation salts based on halogenated TTF and two-dimensional polymeric iodoplumbate or Ag-doped iodoplumbate anions. These salts were ß-(EDT-TTF-I2)2(Pb5/6a1/6I2)3 and ß-(EDT-TTF-I2)2(Pb2/3+xAg1/3-2x??xI2)3, where x = 0.05 and a is a vacancy. Both materials display a metallic response, characteristic of quasi-onedimensional organic conductors. The ß-(EDT-TTF-I2)2(Pb2/3+xAg1/3-2x??xI2)3 salt, with x = 0.05 is partly transparent along the lowest conductivity direction in the infrared frequency range. The single-crystal polarized absorption spectrum recorded in this direction displays a number of vibrational features related to the intramolecular modes of the EDT-TTF-I2 molecule, which are assigned using available normal mode calculations. In addition, the absorption spectrum of the ß-(EDT-TTF-I2)2(Pb2/3+xAg1/3-2xaxI2)3 material dispersed in a KBr pellet is reported and discussed.