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The influence of atmospheric precipitations on the operation of a ship’s radar

Revenko Vitaliy Yu

Zeszyty Naukowe Akademii Morskiej w Szczecinie

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2023

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nr 73 (145)

82--89

EN

The effects of precipitation of varying intensity on the operation of a ship’s radar are considered. It is shown that during the propagation of the electromagnetic wave emitted by the antenna of a ship’s radar, its energy is absorbed by precipitation. To determine the power loss of an electromagnetic wave due to its absorption by particles of precipitation, the effective absorption area, specific absorption coefficient, and specific effective total scattering area are used. The effective areas of absorption and total scattering depend on the shape of the precipitation particles, their size, state of aggregation, and the length of the electromagnetic wave emitted by the antenna of the ship’s radar. The dependence of the effective absorption area on the particle size of precipitation is obtained at two wavelengths of 3 cm and 10 cm, on which the ship’s radars operate. A decrease in the tracking range of an object tracked by a ship’s radar in the case of rain falling is established compared with the tracking range of an object in clear weather. It is shown that a decrease in the tracking range of an object occurs only with moderate, strong, and very heavy rain. The attenuation of electromagnetic energy in rain with an intensity of 12.5 mm/h at a wavelength of 3 cm is obtained by calculation, which amounted to 24 dB with a length of the falling rain zone of 50 km, as well as with rain with an intensity of 100 mm/h with the same length of the precipitation zone.

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Decomposition study of in vivo phytoplankton absorption spectra aimed at identifying the pigments and the phytoplankton group in complex case 2 coastal waters of the Arabian Sea

Shaju S. S., Minu P., Srikanth A. S., Ashraf P. M., Vijayan A. K., Meenakumari B.

Oceanological and Hydrobiological Studies

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2015

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Vol. 44, No. 3

282--293

EN

Phytoplankton modify the optical properties of the seawater by altering the subsurface light field. Information on the accessory pigments present in the phytoplankton helps to differentiate major phytoplankton classes or taxonomic groups. The variability in the absorption spectra of phytoplankton and particulate matter of case 2 coastal waters of the Southeastern Arabian Sea were studied from June 2010 to November 2011. The phytoplankton specific absorption coefficient, at 440 nm and 675 nm, a*ph (440) and a*ph (675) varied from 0.018 to 0.32 m2 mg-1 and from 0.0005 to 0.16 m2 mg-1, respectively. The 4th derivative spectra computed for each in vivo absorption spectrum showed that the amplitude of maxima obtained is proportional to the concentration of the chromoprotein which absorbed that wavelength. Regression of pigment concentration against the 4th derivative spectral coefficient showed that the measurements of particulate absorption could provide quantitative information on chlorophyll a and other accessory pigment concentrations. Fucoxanthin and diadinoxanthin, the carotenoid pigments found in the diatoms were identified from the derivatives peaks. The study demonstrates the utility of using the 4th derivative analysis as a tool to identify the dominating phytoplankton group and its pigment composition.

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Effect of accessory pigment composition on the absorption characteristics of a dinoflagellate bloom in a coastal embayment

Vijayan A. K., Somayajula S. A.

Oceanologia

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2014

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No. 56 (1)

107--124

EN

The light absorption properties of a dinoflagellate (Noctiluca scintillans Macartney) bloom in Manila Bay were analysed during the onset of a whole-bay-scale bloom in March 2004. The chlorophyll a concentrations varied over a very wide range from 1.4 µg l-1 to extremely high values of 521 µg l-1. The chlorophyll specific absorption coefficients of phytoplankton (a*ph(λ)) varied significantly in shape and magnitude. The spectrally averaged values of a*ph(λ) varied by two orders of magnitude within and outside the bloom patch. The total suspended solid concentration was high in the middle of the bay (≥4 mg l-1). The non-photosynthetic pigment (NPP) index was ~0.6 at most of the stations, mainly due to the presence of photoprotective pigments like zeaxanthin, lutein and neoxanthin, which led to variations in the blue absorption maxima of the chlorophyll-specific absorption coefficients. The absorption properties of the accessory pigments were masked owing to the presence of overlapping pigment absorption bands. The fourth derivative of the absorption spectra was able to resolve these overlapping features and enhance the absorption characteristics of prominent accessory pigments.