Acoustic Measurement of Fish Schools Using Array Phase Information

1987 ◽  
Vol 44 (9) ◽  
pp. 1544-1550 ◽  
Author(s):  
G. L. Thomas ◽  
Darrell R. Jackson
Keyword(s):  
Horizontal Plane ◽  
Beam Width ◽  
Target Strength ◽  
Acoustic Measurement ◽  
Phase Information ◽  
Fish Schools ◽  
Fish School ◽  
Blue Whiting ◽  
Beam Directivity ◽  
Better Than

Array phase information on the azimuth and elevation of fish schools allows for beam directivity corrections of target strength, determinations of school depth, and tracking of school movements. When corrected for beam pattern losses, the target strength of blue whiting (Micromesistious poutassou) and rockfish (Sebastes spp.) schools increased approximately 3 dB. The vertical placement of fish schools with the side-scanning split-beam sonar agreed with the fish school depths observed with an echosounder. Split-beam phase was used to track blue whiting schools in the horizontal plane with azimuthal accuracy considerably better than the 3-dB beam width (approximately 20°).

scholarly journals Dual-polarized dipole radiation elements for the modern base station antennas

2019 ◽  
Vol 30 ◽  
pp. 05015
Author(s):  
Vladislav Komov ◽  
Victor Sledkov ◽  
Li ZiMeng
Keyword(s):  
Horizontal Plane ◽  
Beam Width ◽  
Base Station ◽  
Frequency Range ◽  
Dual Polarization ◽  
Dipole Radiation ◽  
Frequency Bands ◽  
Low Level ◽  
Base Station Antennas ◽  
Better Than

Two improved designs of wideband dual polarization antennas for base station. The first design is the crossed dipoles for the frequency bands 1695–2695 MHz. The presented shape of crossed dipole provides a low level of crosspolarization, VSWR better than 1.4, the isolation between polarizations is better than –33 dB and the beam width in the horizontal plane is 65±4 degrees. The second design is the square dipole in the frequency range 690–960 MHz provides the beam width in the horizontal plane 60±5 degrees, E-plane 58±3 degrees, H-plane 64±3 degrees, the isolation between polarizations better than –35dB.

scholarly journals An operational system for automatic school identification on multibeam sonar echoes

2009 ◽  
Vol 66 (5) ◽  
pp. 935-949 ◽  
Author(s):  
Vasilis Trygonis ◽  
Stratis Georgakarakos ◽  
E. John Simmonds
Keyword(s):  
Three Dimensional ◽  
Beam Width ◽  
Multibeam Sonar ◽  
Operational System ◽  
Fish Schools ◽  
Fish School ◽  
School Identification ◽  
Detection And Identification ◽  
Spatio Temporal ◽  
Sonar Echoes

Abstract Trygonis, V., Georgakarakos, S., and Simmonds, E. J. 2009. An operational system for automatic school identification on multibeam sonar echoes. – ICES Journal of Marine Science, 66: 935–949. A system for identifying and tracking fish schools is demonstrated, based on the analysis of multibeam sonar data obtained by a Simrad SP90 long-range sonar. Fish-school detection and identification techniques are similar to those commonly used for vertical echosounders, further enhanced with innovative processing algorithms applied to successive multibeam echograms, increasing the certainty that the identified objects are fish schools. Additionally, analysis of school dynamic parameters facilitates the classification of targets into certain groups, here discriminating the fish aggregating device-natant fish complex from tuna. Statistical analysis of selected tracks quantifies the spatio-temporal variability of the school descriptors, which are used retrospectively to select appropriate analysis thresholds. The algorithms are implemented in an acquisition, visualization, and processing software platform that is flexible regarding sonar characteristics (beam width and number of beams) and can be extended easily to track school echotraces in a three-dimensional mode.

scholarly journals A method for reducing uncertainty in estimates of fish-school frequency response using data from multifrequency and multibeam echosounders

2009 ◽  
Vol 66 (6) ◽  
pp. 1155-1161 ◽  
Author(s):  
Laurent Berger ◽  
Cyrille Poncelet ◽  
Verena M. Trenkel
Keyword(s):  
Frequency Response ◽  
Beam Width ◽  
Multibeam Echosounder ◽  
Fish Schools ◽  
Fish School ◽  
Geographic Coordinate System ◽  
Backscattering Strength ◽  
Adaptive Thresholds ◽  
Exact Position ◽  
Using Data

Abstract Berger, L., Poncelet, C., and Trenkel, V. M. 2009. A method for reducing uncertainty in estimates of fish-school frequency response using data from multifrequency and multibeam echosounders. – ICES Journal of Marine Science, 66: 1155–1161. Fish schools can be insonified simultaneously with multifrequency echosounders (e.g. Simrad EK60s) and a multibeam echosounder (e.g. Simrad ME70). This paper presents a method for combining these data to improve estimates of the relative frequency response r(f) of fish schools. Values of r(f) are now commonly used to classify echoes in fishery surveys. The data from the roll- and pitch-stabilized, high-resolution ME70 are used to correct beam-width effects in the multifrequency EK60 data. First, knowing the exact position and orientation of the transducers and the position of the vessel, the echoes are placed into a common geographic coordinate system. Then, the EK60 data are rejected if they do not include a significant percentage of the fish school imaged with the multibeam echosounder. Echoes that exceed the overlap threshold are used to estimate the r(f). The proposed method is applied to simulated and actual data for sardine and mackerel schools in the Bay of Biscay to estimate their r(f) values. The results for different overlap thresholds are compared with the results of a different method, one that uses adaptive thresholds on volume-backscattering strength Sv. The proposed method reduces uncertainty in estimates of r(f) for schools with an overlap of greater than 80%, and it outperforms the Sv-thresholding technique.

scholarly journals Corrections of fish school area and mean volume backscattering strength by simulation of an omnidirectional multi-beam sonar

2018 ◽  
Vol 75 (4) ◽  
pp. 1496-1508 ◽  
Author(s):  
Vasilis Trygonis ◽  
Zacharias Kapelonis
Keyword(s):  
Three Dimensional ◽  
Simulated Data ◽  
Beam Width ◽  
Dependent Manner ◽  
Cross Sectional ◽  
Density Estimates ◽  
Fish Schools ◽  
Fish School ◽  
Backscattering Strength ◽  
The Difference

Abstract Fish school descriptors extracted from omnidirectional multi-beam data are biased due to beam width-related effects, and echotraces are distorted in a range-dependent manner that is a function of transducer intrinsic properties, as well as fish school characteristics. This work investigates a simulation approach that models the three-dimensional insonification of fish schools by an omnidirectional fishery sonar in order to assess the bias in measuring two key morphometric and energetic descriptors, namely the horizontal cross-sectional area of schools and their mean volume backscattering strength. Simulated fish schools of different sizes and backscattering properties were insonified at various ranges from the multi-beam transducer, outputting volume backscattering strength echograms. The simulated data were used to develop empirical models that correct the examined descriptors using only information extracted from the observed echotraces. Depending on the difference between the observed mean volume backscattering strength of a school and the echogram processing threshold, mean absolute percentage errors in measured area and volume backscatter reduced from 100.7% and 79.5% to 5.2% and 6.4%, respectively. The mean volume backscattering strength of a school is a key parameter for obtaining fish density estimates, and the results highlight the need for descriptor corrections to better interpret the multi-beam data.

Flow Field Inside and Around a Square Fish Cage Considering Fish School Swimming Pattern

2021 ◽  
Author(s):  
Shuchuang Dong ◽  
Sang-gyu Park ◽  
Jinxin Zhou ◽  
Qiao Li ◽  
Takero Yoshida ◽  
...  
Keyword(s):  
Flow Field ◽  
Drag Force ◽  
Current Speed ◽  
Swimming Behavior ◽  
School Structure ◽  
Fish Swimming ◽  
Farmed Fish ◽  
Fish Schools ◽  
Fish School ◽  
Swimming Pattern

Abstract The interaction between fluid and fish cage with stocked fish is extremely complex, including fluid and structure, as well as fluid and fish swimming behavior. The on-current swimming pattern of fish schools was found toward the incoming flow in the previous laboratory studies, which is different from the circular swimming pattern commonly observed in the farming site. In this study, a pseudo fish school structure model (PFS) was proposed to reproduce the five circular swimming patterns of farmed yellowtail, and to investigate the influence of fish school behaviors on the flow field inside and around a model square fish cage in laboratory experiments. The results showed that the drag force acting on the square fish cage increased with the increase of the current speed for all fish school swimming patterns, but no clear difference was observed between the fish school swimming behavior patterns. Overall, the drag force of the square fish cage considering the farmed fish behavior decreased by 11.8%, compared to the drag force of the fish cage without PFS. The current speeds inside and downstream of the fish cage increased almost linearly with increasing current velocities. Compared with the case of the fish cage without PFS, the current speed inside the cage under motionless closely PFS (C0), revolving closely PFS (CR), motionless loosely PFS (L0) and revolving loosely PFS (LR) conditions changed by 10.8%, 9.4%, 65.8% and 39.7%, respectively. In addition, compared to the case of the fish cage without PFS, the current speeds under C0, CR, L0 and LR conditions decreased by 89.8%, 16.3%, 58.2%, and 31.9%, respectively, at 16.0cm downstream from the fish cage, and decreased by 69.2%, 19.4%, 62.7% and 26.3%, respectively, at 63.6cm downstream from the fish cage. Furthermore, the current speed distribution and relative horizontal turbulence intensity distribution inside and around the fish cage under different fish school swimming pattern was discussed. In the future, we will use live fish to conduct experiments to evaluate fish school models.

Design, Fabrication and Test of Modified Septum Antennas for Satellite Telecommunication

Frequenz ◽  
2018 ◽  
Vol 72 (7-8) ◽  
pp. 301-313 ◽  
Author(s):  
Mohammad Fazaelifar ◽  
Shahrokh Jam ◽  
Raheleh Basiri ◽  
H. Reza Azadi
Keyword(s):  
Axial Ratio ◽  
Beam Width ◽  
Center Frequency ◽  
Low Loss ◽  
Ground Station ◽  
Large Bandwidth ◽  
Low Weight ◽  
Measurement Results ◽  
Novel Design ◽  
Better Than

Abstract In this paper at first, the ordinary septum polarizer has been designed and used for parabolic reflector feed in Ground station antenna. Next, a novel design of modified septum polarizer with wider beam-width is proposed for satellite antenna. Compactness, low weight, large bandwidth, high TX/RX isolation, low axial ratio as well as low loss are the advantages of the septum polarizer. The designed antenna has high purity circular polarization ( $\left| {AR} \right| \le 1.6dB$ ) and low return loss. The frequency bandwidth of the antenna is about 27 % in the center frequency 11 GHz and the TX/RX isolation is better than 32 dB. Finally the septum polarizer, modified septum polarizer and reflector are fabricated and tested and there were good agreement between simulation and measurement results.

scholarly journals In situ target strength estimates of optically verified southern blue whiting (Micromesistius australis)

2012 ◽  
Vol 70 (2) ◽  
pp. 431-439 ◽  
Author(s):  
Richard L. O'Driscoll ◽  
Johannes Oeffner ◽  
Adam J. Dunford
Keyword(s):  
New Zealand ◽  
Confidence Interval ◽  
Fork Length ◽  
Target Strength ◽  
Blue Whiting ◽  
Acoustic Target ◽  
The Mean ◽  
The Relationship ◽  
Immature Fish

Abstract O'Driscoll, R. L., Oeffner, J., and Dunford, A. J. 2013. In situ target strength estimates of optically verified southern blue whiting (Micromesistius australis) – ICES Journal of Marine Science, 70: 431–439. Estimates of the acoustic target strength (TS) of southern blue whiting (Micromesistius australis) at 38 kHz were obtained using an autonomous acoustic–optical system (AOS) mounted on a demersal trawl. Data were collected from aggregations of spawning adult [mean fork length (FL) 34.4 cm] and immature (mean FL 24.6 cm) southern blue whiting south of New Zealand. Mean TS was estimated from 162 tracks containing 695 echoes from targets identified from video as southern blue whiting. The mean TS was –37.9 dB with a 95% confidence interval (CI) of –39.7 to –36.6 dB for 21 immature fish and –34.6 dB (95% CI –35.4 to –34.0 dB) for 141 adults. A logarithmic fit through the mean TS values produced a TS–fork length (FL) relationship from optically verified targets of TS = 22.06 log10FL – 68.54. This new relationship gives TS values within 1 dB of those estimated using the relationship recently adopted by ICES for blue whiting (Micromesistius poutassou) of TS = 20 log10TL – 65.2 (where TL is total length) obtained from in situ measurements, but higher values than those estimated from the previous relationship for southern blue whiting of TS = 38 log10FL – 97, which was based on swimbladder modelling.

scholarly journals Bags-of-Features for fish school cluster characterization in pelagic ecosystems: application to the discrimination of juvenile and adult anchovy (Engraulis ringens) clusters off Peru

2012 ◽  
Vol 69 (8) ◽  
pp. 1329-1339 ◽  
Author(s):  
Ronan Fablet ◽  
Paul Gay ◽  
Salvador Peraltilla ◽  
Cecilia Peña ◽  
Ramiro Castillo ◽  
...  
Keyword(s):  
Data Sets ◽  
Correct Classification ◽  
Classification Rate ◽  
Fish Schools ◽  
Fish School ◽  
Acoustic Data ◽  
School Based ◽  
Engraulis Ringens ◽  
Fisheries Acoustics

Whereas fisheries acoustics data processing mainly focused on the detection, characterization, and recognition of individual fish schools, here we addressed the characterization and discrimination of fish school clusters. The proposed scheme relied on the application of the Bags-of-Features (BoF) approach to acoustic echograms. This approach is widely exploited for pattern recognition issues and naturally applies here, considering fish schools as the relevant elementary objects. It relies on the extraction and categorization of fish schools in fisheries acoustic data. Echogram descriptors were computed per unit echogram length as the numbers of schools in different school categories. We applied this approach to the discrimination of juvenile and adult anchovy ( Engraulis ringens ) off Peru. Whereas the discrimination of individual schools is low (below 70%), the proposed BoF scheme achieved between 89% and 92% of correct classification of juvenile and adult echograms for different survey data sets and significantly outperformed classical school-based echogram characteristics (about 10% of improvement of the correct classification rate). We further illustrate the potential of the proposed scheme for the estimation of the spatial distribution of juvenile and adult anchovy populations.

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