Acoustic Detection of Demersal Fish Closer than 15 Centimetres to the Bottom in 80 Metres of Water

1978 ◽  
Vol 35 (8) ◽  
pp. 1155-1156 ◽  
Author(s):  
M. H. Orr ◽  
E. E. Hays ◽  
F. R. Hess
Keyword(s):  
Key Words ◽  
Demersal Fish ◽  
Ocean Bottom ◽  
Acoustic Detection ◽  
Acoustic Backscattering ◽  
System Operating

Records from an acoustic backscattering system operating at 200 kHz are presented which show that demersal fish can be individually detected closer than 15 cm to the ocean bottom in 88 m of water. Key words: acoustic, demersal fish

scholarly journals Acoustic Detection of Oceanic Double-Diffusive Convection: A Feasibility Study

2010 ◽  
Vol 27 (3) ◽  
pp. 580-593 ◽  
Author(s):  
Tetjana Ross ◽  
Andone Lavery
Keyword(s):  
Acoustic Scattering ◽  
Double Diffusive Convection ◽  
Western Antarctic Peninsula ◽  
Acoustic Detection ◽  
Acoustic Backscattering ◽  
Diffusive Regime ◽  
Diffusive Convection ◽  
In Situ Observations ◽  
Double Diffusive

Abstract The feasibility of using high-frequency acoustic scattering techniques to map the extent and evolution of the diffusive regime of double-diffusive convection in the ocean is explored. A scattering model developed to describe acoustic scattering from double-diffusive interfaces in the laboratory, which accounted for much of the measured scattering in the frequency range from 200 to 600 kHz, is used in conjunction with published in situ observations of diffusive-convection interfaces to make predictions of acoustic scattering from oceanic double-diffusive interfaces. Detectable levels of acoustic scattering are predicted for a range of different locations in the world’s oceans. To corroborate these results, thin acoustic layers detected near the western Antarctic Peninsula using a multifrequency acoustic backscattering system are shown to be consistent with scattering from diffusive-convection interfaces.

scholarly journals The Rhizomatic Trajectory of Ecocriticism

2010 ◽  
Vol 1 (1) ◽  
Author(s):  
Serpil Oppermann
Keyword(s):  
Key Words ◽  
Theory And Practice ◽  
Hierarchical System ◽  
Third Wave ◽  
Deleuze And Guattari ◽  
Palabras Clave ◽  
Interpretive Methods ◽  
System Operating

Key words: rhizomatic trajectory, third wave, postmodern ecocriticism, Deleuze and Guattari, interconnected approaches, ecocritical heterogeneity, multiplicity of theories  In its third wave, ecocriticism has become multicultural and transnational, and expanded rapidly in terms of epistemological positions and interpretive methods. Its very multiple directions and methodological and theoretical plurality may appear problematic. However, ecocritical theory and practice are not arbitrary or ‘ambivalently open’, but rather pursue a trajectory summed up by Deleuze and Guattari in the image of the rhizome. The quintessentially postmodern concept of the rhizome as an acentred, non-hierarchical system operating by variation and alliance permits us to recognise a cultivated kind of growth where others have seen only disciplinary crisis.  Palabras clave: trayectoria rizomática, tercera oleada, ecocrítica posmoderna, Deleuze y Guattari, enfoques interconectados, heterogeneidad ecocrítica, multiplicidad de teorías  En esta tercera oleada, la ecocrítica se ha vuelto multicultural y transnacional, y se ha expandido rápidamente en lo que respecta a posiciones epistemológicas y a métodos interpretativos. Sus múltiples direcciones y su pluralidad metodológica y teórica pueden parecer problemáticas. Sin embargo, la teoría y prácticas ecocríticas no son arbitrarias o “abiertas de forma ambivalente”, sino que más bien continúan una trayectoria que Deleuze y Guattari han resumido en la imagen del rizoma. El concepto postmodernista por excelencia del rizoma es un sistema no-jerárquico y sin centro que se rige por la variedad y la alianza y que nos permite reconocer un tipo de crecimiento cultivado donde otros sólo han visto una crisis disciplinaria.  

scholarly journals Acoustic backscattering at low grazing angles from the ocean bottom. I. Bottom backscattering strength

1984 ◽  
Vol 75 (S1) ◽  
pp. S30-S30 ◽  
Author(s):  
H. Boehme ◽  
N. P. Chotiros ◽  
L. D. Rolleigh ◽  
S. P. Pitt ◽  
A. L. Garcia ◽  
...  
Keyword(s):  
Ocean Bottom ◽  
Acoustic Backscattering ◽  
Backscattering Strength ◽  
Grazing Angles

scholarly journals Effect of Suspended Sediment on Acoustic Detection Using Reverberation

2005 ◽  
Vol 39 (2) ◽  
pp. 105-109 ◽  
Author(s):  
Peter C. Chu ◽  
Michael Cornelius ◽  
Mel Wagstaff
Keyword(s):  
Suspended Sediment ◽  
Sediment Layer ◽  
Acoustic Detection ◽  
Acoustic Characteristics ◽  
Volume Scattering ◽  
Acoustic Backscattering ◽  
Acoustic Simulation ◽  
Line Array ◽  
Buried Object ◽  
Scattering Strength

Sonar operates by ensonifying a broad swath of the seabed using a line array of acoustic projectors with acoustic backscattering from the ensonified sediment. The suspended sediment layer affects the sonar imagery through the volume scattering strength. Understanding the acoustic characteristics of the suspended sediment layer can aid the Navy in detecting sea mines with sonar imagery. In this study, the Navy's Comprehensive Acoustic Simulation System is used to investigate such an effect. A range of critical values of volume scattering strength for buried object detection is found through repeated model simulations.

Convergence of Acoustic, Optical, and Net-Catch Estimates of Euphausiid Abundance: Use of Artificial Light to Reduce Net

1993 ◽  
Vol 50 (2) ◽  
pp. 334-346 ◽  
Author(s):  
D. Sameoto ◽  
N. Cochrane ◽  
A. Herman
Keyword(s):  
Target Strength ◽  
Sampling System ◽  
Remotely Operated Vehicle ◽  
Acoustic Backscattering ◽  
Video Cameras ◽  
Acoustic Target ◽  
Avoidance Reactions ◽  
Theoretical Scattering ◽  
System Operating

Euphausiid concentrations in the Scotian Shelf basins were sampled with BIONESS, a multinet sampling system, and quantitatively assessed simultaneously with an in situ optical zooplankton counter (OPC) mounted on BIONESS and with an acoustic backscattering system operating simultaneously at 50, 122, and 200 kHz. Supplementary observations were made with vertically dropped video cameras and video and 35-mm frame cameras mounted on a remotely operated vehicle (ROV). The use of a light source on BIONESS during sampling increased the catch of euphausiids by 10–20 times by reducing active avoidance reactions to the net. Consequently, conventional net sampling has greatly underestimated euphausiid concentrations, a conclusion suggested by previous acoustic measurements. Experimental acoustic target strengths for 28-mm euphausiids averaged −77.5, −73.4, and −68.4 dB at 50, 122, and 200 kHz, respectively, using measured Sv levels and assuming 100% net sampling efficiency. Theoretical scattering models based on randomly oriented cylinders require the euphausiids to be oriented within about 5° of the horizontal to approximate both the experimentally observed target strength amplitudes and their frequency dependence. Acoustic interpretation has been enhanced by incorporation of transducer sensitivity versus temperature corrections and modeling techniques that allow for finite transducer beam widths.

scholarly journals Estimating gear efficiency in a combined acoustic and trawl survey, with reference to the spatial distribution of demersal fish

2009 ◽  
Vol 67 (4) ◽  
pp. 668-676 ◽  
Author(s):  
Mathieu Doray ◽  
Stéphanie Mahévas ◽  
Verena M. Trenkel
Keyword(s):  
Spatial Distribution ◽  
Demersal Fish ◽  
Target Strength ◽  
Fish Length ◽  
Trawl Survey ◽  
Acoustic Backscattering ◽  
Scattering Coefficients ◽  
Fishing Vessels ◽  
Gear Efficiency ◽  
The Mean

Abstract Doray, M., Mahévas, S., and Trenkel, V. M. 2010. Estimating gear efficiency in a combined acoustic and trawl survey, with reference to the spatial distribution of demersal fish. – ICES Journal of Marine Science, 67: 668–676. Few analyses have been performed to estimate the efficiency of trawls targeting demersal fish using the ratio of catches and acoustic densities. In summer 2006, acoustic and fishing data were collected simultaneously over 3 d by three fishing vessels equipped with identical pelagic trawls in the Bay of Biscay. Variography identified moderate spatial autocorrelation in the acoustic backscatter at a mean scale of 3 km, a scale slightly smaller than the mean haul length (3.5 km), indicating that fish horizontal availability did not influence trawl efficiency. Acoustic backscattering densities expressed as nautical area scattering coefficients (NASCs) recorded in the trawled layer were compared with equivalent NASC (ENASC) values calculated from the species composition in the trawl, fish-length structure, and available relationships between target strength and fish length. Estimates of trawl efficiency for hake-dominated trawls were computed as the slopes of the relationships ENASC = 0.008 NASC and ENASC = 0.18 NASC0.31 for trawls made by day and night, respectively. For the whole demersal community, the relationships were ENASC = 0.022 NASC and ENASC = 0.17 NASC0.33 for trawls made by day and night, respectively.

High‐frequency acoustic backscattering from a coarse shell ocean bottom

1989 ◽  
Vol 85 (1) ◽  
pp. 125-136 ◽  
Author(s):  
S. Stanic ◽  
K. B. Briggs ◽  
P. Fleischer ◽  
W. B. Sawyer ◽  
R. I. Ray
Keyword(s):  
High Frequency ◽  
Ocean Bottom ◽  
Acoustic Backscattering
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