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Article
Volume backscattering spectra measurements of Antarctic krill using a broadband echosounder
For the acoustic inference of lengths and orientation angles of Antarctic krill (krill), reliable theoretical acoustic scattering models and parameters are necessary. To measure the volume backscattering (SV) ...
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Article
Effects of fast Fourier transform window size on the target strength spectra of tungsten carbide spheres
The window size (WS) of the fast Fourier transform (FFT) is one of the important parameters when calculating target strength (TS) spectra from broadband echo waveforms. However, the effects of the FFT WS on TS...
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Article
Estimated ammonium regeneration potentials of two common euphausiid species (Euphausia superba and E. crystallorophias) off Adélie Land, East Antarctica, in austral summer, 2008
Zooplankton contribute to nitrogen regeneration for primary productivity via ammonium excretion. To improve our understanding of the biogeochemical role of zooplankton in the Southern Ocean, ammonium excretion...
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Article
Annual variation of oceanographic conditions changed migration timing of bowhead whales Balaena mysticetus in the southern Chukchi Sea
The Chukchi Sea environment changes considerably in physical and biological conditions, driven by the expanding volume of warm Pacific summer water. These environmental changes can affect the migration timing ...
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Article
A broadband target strength measurement method for weakly scattering animals using a 50-ms-long linear frequency modulated signal in a small tank
We built a new pulse-echo system using a small tank (1 × 1 × 1 m) for measuring the broadband target strength of weakly scattering animals such as krill and shrimp. The system transmits a linear frequency modu...
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Article
Open AccessPossible fluid discharge associated with faults observed by a high-resolution dense-2D seismic reflection survey in Uchiura Bay off Numazu, Japan
Although fluid behavior along faults has often been associated with earthquakes and hydrocarbon accumulation, few observations of active, ongoing fluid discharge along the faults exist. We conducted a dense-2D...
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Article
Open AccessA new seismic survey technology using underwater speaker detected a low-velocity zone near the seafloor: an implication of methane gas accumulation in Tokyo Bay
Owing to the strict restrictions on the use of air guns in marine seismic surveys due to concerns about their potential impact on the marine ecosystem, there have been several cases where seismic surveys were ...
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Article
Estimation of target strength of Sardina pilchardus and Sardinella aurita by theoretical approach
The target strength (TS) patterns of Sardina pilchardus and Sardinella aurita at 38 and 120 kHz were estimated by a prolate-spheroid model, using measurements of swimbladder length and width. The ratio of swimbla...
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Article
Basin-scale distribution pattern and biomass estimation of Japanese anchovy Engraulis japonicus in the western North Pacific
The distribution pattern and biomass of the Japanese anchovy Engraulis japonicus in the offshore region of the western North Pacific (north of 35°N and west of 170°E) were studied using a quantitative echosounder...
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Article
Multilayer biological structure and mixing in the upper water column of Lake Biwa during summer 2008
We carried out a 24-h station experiment at Lake Biwa (Japan) to measure mixing events and concurrent biological signals using a free-fall microstructure profiler (TurboMAP-L), conventional hydrographic measur...
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Article
Pelagic fish distribution and ontogenetic vertical migration in common mesopelagic species off Lützow-Holm Bay (Indian Ocean sector, Southern Ocean) during austral summer
The horizontal and vertical distributions of fish were examined off Lützow-Holm Bay in the Indian Ocean sector of the Southern Ocean during midnight sun in January 2005. Fish were sampled from six discrete dep...
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Article
Measurement of sea bottom surface backscattering strength by quantitative echo sounder
Measurement theory and method of the bottom surface backscattering strength (SS) using a quantitative echo sounder (QES) are discussed and applied in the ocean near Java, Indonesia. The frequencies of the QES ...