scholarly journals RESULTS OF EXPERIMENTAL HYDROACOUSTIC RESEARCHES ON EVALUATION OF SPATIAL DISTRIBUTION OF STURGEON UNDERYEARLINGS IN SHALLOW WATERS OF THE NORTHERN CASPIAN IN 2017

2019 ◽  
pp. 7-12
Author(s):  
Igor Borisovich Balchenkov ◽  
Tatiana Vasilievna Pomogaeva
Keyword(s):  
Shallow Water ◽  
Marine Fish ◽  
Sharp Decrease ◽  
Design Bureau ◽  
Near Surface ◽  
Acoustic Data ◽  
Vertical Location ◽  
Acoustic Surveys ◽  
Significant Underestimation ◽  
Research Institute

Since 2005, in the Russian part of the Northern Caspian, Caspian Research Institute of Fisheries has been conducting trawl-acoustic surveys to solve problems in determining the density, biomass and seasonal dynamics of commercial marine fish species. Recently, special attention has been paid to the estimation of the number of sturgeon fishes and their juveniles due to a sharp decrease in the concentrations of these fish in the areas of traditional trawl-acoustic surveys. Until 2015, sonar studies were carried out with the help of a fishfinder echosounder - a video plotter PEV-K, created in the Design Bureau of Marine Electronics “Vector” (Taganrog, Russia). Taking into account the shallow water of the Northern Caspian (depth 3-10 m), this echo sounder of the vertical location gave an insufficiently qualitative quantitative estimate of marine fish concentrations. According to the latest works in the field of acoustics on shallow water bodies, significant shortcomings in the use of vertical echolocation only have been identified, due to a significant underestimation of fish in the near-surface layer in shallow water conditions. It is proved that the most optimal alternative for conducting trawl-acoustic surveys is the simultaneous use of vertical and horizontal echolocation. Solving the actual problems of obtaining representative acoustic data, Caspian Research Institute of Fisheries acquired EY-60 hydroacoustic complex from “Simrad”, using the complex allows simultaneous horizontal and vertical echolocation. Within 2015-2017, with the help of this complex, a survey considering sturgeon yearlings was regularly conducted in the Northern Caspian.

scholarly journals Limitations of target detection in horizontal acoustic surveys of extremely shallow water bodies

2019 ◽  
Vol 218 ◽  
pp. 94-104
Author(s):  
Ievgen Koliada ◽  
Helge Balk ◽  
Michal Tušer ◽  
Ladislav Ptáček ◽  
Jan Kubečka
Keyword(s):  
Shallow Water ◽  
Target Detection ◽  
Water Bodies ◽  
Acoustic Surveys

A multifrequency method to classify and evaluate fisheries acoustics data

2006 ◽  
Vol 63 (10) ◽  
pp. 2225-2235 ◽  
Author(s):  
J Michael Jech ◽  
William L Michaels
Keyword(s):  
Clupea Harengus ◽  
Biological Information ◽  
Classification Algorithms ◽  
Atlantic Herring ◽  
Population Abundance ◽  
Acoustic Data ◽  
Video Images ◽  
Abundance Estimates ◽  
Fisheries Acoustics ◽  
Acoustic Surveys

Acoustic surveys have been conducted on Georges Bank from 1998 to present to estimate Atlantic herring (Clupea harengus) population abundance. Acoustic data were collected with a 12 or 18, 38, and 120 kHz Simrad EK500 scientific echo sounder. A pelagic trawl and underwater video images were used to collect biological information and to verify the species composition of acoustic backscatter. A multifrequency classification method was developed to improve the efficiency and accuracy of classifying species from acoustic echograms. In this method, a volume backscatter (Sv) threshold was applied equivalently to all echograms, and then a composite echogram was created based on which frequencies had Sv greater than or less than the Sv threshold. The results of this method were compared with the standard method of visually scrutinizing regions, and metrics were developed to evaluate the accuracy of classification algorithms relative to current methods, as well as to assess the effects of classification methods on population abundance estimates. In general, this method matched visually scrutinized Atlantic herring regions, but with consistent biases in classifying 38 kHz backscatter. The metrics highlighted spatial and temporal changes in the acoustic landscape, which may be indicative of intra- and inter-annual biological changes.

Geoacoustic inversion in shallow water using broadband synthetic aperture and single hydrophone acoustic data

2011 ◽  
Vol 130 (4) ◽  
pp. 2391-2391
Author(s):  
Bien Aik Tan ◽  
Peter Gerstoft ◽  
Caglar Yardim ◽  
William Hodgkiss
Keyword(s):  
Shallow Water ◽  
Synthetic Aperture ◽  
Geoacoustic Inversion ◽  
Acoustic Data

Near‐surface source depth resolution in a shallow‐water environment

1997 ◽  
Vol 102 (5) ◽  
pp. 3171-3171
Author(s):  
W. S. Hodgkiss ◽  
J. J. Murray ◽  
N. O. Booth ◽  
P. W. Schey
Keyword(s):  
Shallow Water ◽  
Water Environment ◽  
Depth Resolution ◽  
Source Depth ◽  
Surface Source ◽  
Near Surface ◽  
Shallow Water Environment

scholarly journals Boat-towed radio-magnetotelluric and controlled source audio-magnetotelluric study to resolve fracture zones at Äspö Hard Rock Laboratory site, Sweden

2019 ◽  
Vol 218 (2) ◽  
pp. 1008-1031 ◽  
Author(s):  
Shunguo Wang ◽  
Mehrdad Bastani ◽  
Steven Constable ◽  
Thomas Kalscheuer ◽  
Alireza Malehmir
Keyword(s):  
Shallow Water ◽  
Penetration Depth ◽  
Large Scale ◽  
Hard Rock ◽  
High Water ◽  
Fracture Zones ◽  
Geological Structures ◽  
Near Surface ◽  
Controlled Source ◽  
Rock Laboratory

SUMMARY Boat-towed radio-magnetotelluric (RMT) measurements using signals between 14 and 250 kHz have attracted increasing attention in the near-surface applications for shallow water and archipelago areas. A few large-scale underground infrastructure projects, such as the Stockholm bypass in Sweden, are planned to pass underneath such water zones. However, in cases with high water salinity, RMT signals have a penetration depth of a few metres and do not reach the geological structures of interest in the underlying sediments and bedrock. To overcome this problem, controlled source signals at lower frequencies of 1.25 to 12.5 kHz can be utilized to improve the penetration depth and to enhance the resolution for modelling deeper underwater structures. Joint utilization of boat-towed RMT and controlled source audio-magnetotellurics (CSAMT) was tested for the first time at the Äspö Hard Rock Laboratory (HRL) site in south-eastern Sweden to demonstrate acquisition efficiency and improved resolution to model fracture zones along a 600-m long profile. Pronounced galvanic distortion effects observed in 1-D inversion models of the CSAMT data as well as the predominantly 2-D geological structures at this site motivated usage of 2-D inversion. Two standard academic inversion codes, EMILIA and MARE2DEM, were used to invert the RMT and CSAMT data. EMILIA, an object-oriented Gauss–Newton inversion code with modules for 2-D finite difference and 1-D semi-analytical solutions, was used to invert the RMT and CSAMT data separately and jointly under the plane-wave approximation for 2-D models. MARE2DEM, a Gauss–Newton inversion code for controlled source electromagnetic 2.5-D finite element solution, was modified to allow for inversions of RMT and CSAMT data accounting for source effects. Results of EMILIA and MARE2DEM reveal the previously known fracture zones in the models. The 2-D joint inversions of RMT and CSAMT data carried out with EMILIA and MARE2DEM show clear improvement compared with 2-D single inversions, especially in imaging uncertain fracture zones analysed in a previous study. Our results show that boat-towed RMT and CSAMT data acquisition systems can be utilized for detailed 2-D or 3-D surveys to characterize near-surface structures underneath shallow water areas. Potential future applications may include geo-engineering, geohazard investigations and mineral exploration.

Analysis of shallow-water experimental acoustic data including a comparison with a broad-band normal-mode-propagation model

2001 ◽  
Vol 26 (3) ◽  
pp. 308-323 ◽  
Author(s):  
D.G. Simons ◽  
R. McHugh ◽  
M. Snellen ◽  
N.H. McCormick ◽  
E.A. Lawson
Keyword(s):  
Shallow Water ◽  
Normal Mode ◽  
Broad Band ◽  
Propagation Model ◽  
Mode Propagation ◽  
Acoustic Data

scholarly journals Observations and a Model of the Mean Circulation over the Middle Atlantic Bight Continental Shelf

2008 ◽  
Vol 38 (6) ◽  
pp. 1203-1221 ◽  
Author(s):  
Steven J. Lentz
Keyword(s):  
Pressure Gradient ◽  
Continental Shelf ◽  
Shallow Water ◽  
Water Depth ◽  
Circulation Pattern ◽  
Near Surface ◽  
Middle Atlantic ◽  
The Mean ◽  
Offshore Flow ◽  
Mean Circulation

Abstract Analyses of current time series longer than 200 days from 33 sites over the Middle Atlantic Bight continental shelf reveal a consistent mean circulation pattern. The mean depth-averaged flow is equatorward, alongshelf, and increases with increasing water depth from 3 cm s−1 at the 15-m isobath to 10 cm s−1 at the 100-m isobath. The mean cross-shelf circulation exhibits a consistent cross-shelf and vertical structure. The near-surface flow is typically offshore (positive, range −3 to 6 cm s−1). The interior flow is onshore and remarkably constant (−0.2 to −1.4 cm s−1). The near-bottom flow increases linearly with increasing water depth from −1 cm s−1 (onshore) in shallow water to 4 cm s−1 (offshore) at the 250-m isobath over the slope, with the direction reversal near the 50-m isobath. A steady, two-dimensional model (no along-isobath variations in the flow) reproduces the main features of the observed circulation pattern. The depth-averaged alongshelf flow is primarily driven by an alongshelf pressure gradient (sea surface slope of 3.7 × 10−8 increasing to the north) and an opposing mean wind stress that also drives the near-surface offshore flow. The alongshelf pressure gradient accounts for both the increase in the alongshelf flow with water depth and the geostrophic balance onshore flow in the interior. The increase in the near-bottom offshore flow with water depth is due to the change in the relative magnitude of the contributions from the geostrophic onshore flow that dominates in shallow water and the offshore flow driven by the bottom stress that dominates in deeper water.

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