A hydrodynamic analytical model of fish tilt angle: Implications regarding acoustic target strength modelling

2018 ◽  
Vol 387 ◽  
pp. 70-82
Author(s):  
F. Agustín Membiela ◽  
Matías G. dell’Erba
Keyword(s):  
Analytical Model ◽  
Tilt Angle ◽  
Target Strength ◽  
Acoustic Target

scholarly journals The effects of swimbladder size, condition and gonads on the acoustic target strength of mature capelin

2003 ◽  
Vol 60 (5) ◽  
pp. 1056-1062 ◽  
Author(s):  
Roar Jørgensen
Keyword(s):  
Tilt Angle ◽  
Barents Sea ◽  
Condition Factor ◽  
Target Strength ◽  
Gonad Weight ◽  
The Barents Sea ◽  
Size Condition ◽  
Negative Effect ◽  
Acoustic Target ◽  
Post Spawning

Abstract Pre- and post-spawning capelin from the Barents Sea stock were observed in a net pen with a calibrated 38 kHz scientific split-beam echosounder. The transducer was positioned vertically or tilted. The acoustic target strength (TS) of capelin depended on swimbladder length. In female capelin within 15.5–18.0 cm length the logarithm of weight was significantly negatively related to TS. The negative effect of weight on TS could be due to a higher condition factor (assumed higher fat content), which gave the fish additional buoyancy and less need for swimbladder volume. The effect of gonad weight on TS was not significant. Comparisons of measurements made with vertical and tilted transducers demonstrated a small but significant effect of tilt angle on TS.

Ex situ acoustic target strength by tilt angle and pulsation of moon jellyfish (Aurelia aurita) using frequency 70 kHz

2015 ◽  
Vol 51 (3) ◽  
pp. 295-301
Author(s):  
Eun–A YOON ◽  
Doo–Jin HWANG ◽  
HIROSE Miyuki ◽  
Kouichi SAWADA ◽  
Yoshiaki FUKUDA ◽  
...  
Keyword(s):  
Tilt Angle ◽  
Aurelia Aurita ◽  
Ex Situ ◽  
Target Strength ◽  
Moon Jellyfish ◽  
Acoustic Target

scholarly journals The influence of tilt angle on the acoustic target strength of the Japanese common squid (Todarodes pacificus)

2005 ◽  
Vol 62 (4) ◽  
pp. 779-789 ◽  
Author(s):  
Donhyug Kang ◽  
Tohru Mukai ◽  
Kohji Iida ◽  
Doojin Hwang ◽  
Jung-Goo Myoung
Keyword(s):  
Tilt Angle ◽  
Empirical Relationship ◽  
Ex Situ ◽  
Target Strength ◽  
Todarodes Pacificus ◽  
Common Squid ◽  
Acoustic Target ◽  
The Mean ◽  
Highly Correlated ◽  
Japanese Common Squid

Abstract To measure the influence of changes in tilt angle on the acoustic target strength (TS) of the Japanese common squid (Todarodes pacificus), we conducted a series of experiments to estimate TS in relation to tilt angle and swimming angle. Swimming angle was measured in a seawater tank using two infrared, underwater cameras under dark conditions. Ex situ measurements of TS in relation to tilt angle on live specimens using a fishhook and cage method were then conducted at 38 and 120 kHz; mantle length (ML) ranged from 21 to 27 cm (mean 24.75 cm). For the more precise TS measurement with tilt angle, another set of ex situ TS measurements relative to tilt angle was made at 38 and 120 kHz on tethered, anesthetized specimens in seawater. The mean swimming angle was −17.7° (±12.7° s.d.). The mean TS varied from −48.6 to −44.6 dB and was relatively higher at 120 kHz than at 38 kHz, in the order of 0.7 and 2.5 dB. The empirical relationship between TS (dB) and ML (cm) is given by TS = 20 log10(ML) − 75.4 (r = 0.81) at 38 kHz or TS = 20 log10(ML) − 73.5 (r = 0.64) at 120 kHz. Based on the tethered method for the anesthetized squid, the mean standardized TS values (b20) were found to be highly correlated with the tilt angle, and the resultant fitted equations for b20 were expressed as: b20 = −73.3 + 0.48 × Θ + 0.0122 × Θ2 + 0.00016 × Θ3 for 38 kHz and b20 = −72.6 + 0.53 × Θ + 0.0134 × Θ2 + 0.00014 × Θ3 for 120 kHz, where Θ is the negative tilt angle in degrees. The mean TS based on the measurements using live squid was higher than that of tethered measurements, i.e., 2.6 dB at 38 kHz and 4.0 dB at 120 kHz. The higher mean TS in the ex situ measurements for the live squid can be explained by the influence of the low tilt angle on the overall TS data. The results can be used to understand the influence of tilt angle on the TS of Todarodes pacificus and thus improve the accuracy of biomass estimates.

scholarly journals Target strength and tilt-angle distribution of the lesser sandeel (Ammodytes marinus)

2012 ◽  
Vol 69 (6) ◽  
pp. 1099-1107 ◽  
Author(s):  
Rokas Kubilius ◽  
Egil Ona
Keyword(s):  
Tilt Angle ◽  
Field Experiments ◽  
Video Camera ◽  
Target Strength ◽  
Fish Length ◽  
Angle Distribution ◽  
Total Uncertainty ◽  
Sea Bottom ◽  
Swimming Pattern ◽  
Acoustic Target

Abstract Kubilius, R., and Ona, E. 2012. Target strength and tilt-angle distribution of lesser sandeel (Ammodytes marinus) – ICES Journal of Marine Science, 69: 1099–1107. North Sea stocks of lesser sandeel have recently become depleted, and improved methods for abundance estimation are sought. This paper focuses on the acoustic target strength (TS) and orientation of sandeel, measured simultaneously in several field experiments. A specially designed cubic cage, fitted with an echosounder and a video camera, was lowered onto the sea bottom, trapping wild sandeel inside. Methods for manually selecting valid echotraces from individual sandeel are described. Scattered mean TS values from several experiments are reported. These are, in spite of the observed variability, summarized in a TS–fish length (cm) relationship as TS = 20logL – 93.1 (dB) at 200 kHz. We believe that the accuracy of the relationship may still be debated; incorporating larger uncertainty in the overall mean TS will increase the total uncertainty of the stock biomass estimate from sandeel acoustic surveys. This uncertainty is now, using standard narrow-beam echosounders, dominated by the fish patchiness relative to the survey coverage. Results from pilot investigations of the sandeel swimming orientation using video cameras are also presented, showing that sandeel usually has an anguilliform swimming pattern with substantial positive (head-up) tilt. The spread of the tilt-angle distribution is also larger than for more neutrally buoyant fishes.

Development of acoustic target strength near-field equation for underwater vehicles

2018 ◽  
Vol 233 (3) ◽  
pp. 714-721
Author(s):  
Jae-Yong Kim ◽  
Suk-Yoon Hong ◽  
Byung-Gu Cho ◽  
Jee-Hun Song ◽  
Hyun-Wung Kwon
Keyword(s):  
Field Equation ◽  
Plane Wave ◽  
Pressure Field ◽  
Near Field ◽  
Target Strength ◽  
Detection Capability ◽  
Weapon Systems ◽  
Active Sonar ◽  
Acoustic Target ◽  
Definition Of

For modern weapon systems, the most important factor in survivability is detection capability. Acoustic target strength is a major parameter of the active sonar equation. The traditional target strength equation used to predict the re-radiated intensity for the far field is derived with a plane-wave assumption. In this study, a near-field target strength equation was derived without a plane-wave assumption for a polygonal plate. The target strength equation for polygonal plates, which is applicable to the near field, is provided by the Helmholtz–Kirchhoff formula that is used as the primary equation for solving the re-radiated pressure field. A generalized definition of the sonar cross section is suggested that is applicable to the near field. In comparison experiments for a cylinder, the target strength equation for polygonal plates in near field was executed to verify the validity and accuracy of the analysis. In addition, an underwater vehicle model was analyzed with the developed near-field equation to confirm various parameter effects such as distance and frequency.

scholarly journals The study of the acoustic target strength of Chub mackerel in the northwestern Pacific Ocean in situ

Trudy VNIRO ◽  
2021 ◽  
Vol 184 ◽  
pp. 73-86
Author(s):  
M.Yu. Kuznetsov ◽  
◽  
V.I. Polyanichko ◽  
E.V. Syrovatkin ◽  
I.A. Ubarchuk ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Target Strength ◽  
Northwestern Pacific ◽  
Chub Mackerel ◽  
Northwestern Pacific Ocean ◽  
Acoustic Target

First in situ estimates of acoustic target strength of Antarctic toothfish (Dissostichus mawsoni)

2018 ◽  
Vol 206 ◽  
pp. 79-84 ◽  
Author(s):  
Richard L. O’Driscoll ◽  
Simonepietro Canese ◽  
Yoann Ladroit ◽  
Steve J. Parker ◽  
Laura Ghigliotti ◽  
...  
Keyword(s):  
Target Strength ◽  
Antarctic Toothfish ◽  
Dissostichus Mawsoni ◽  
Acoustic Target

scholarly journals A Modified Analytical Heat Source Model for Numerical Simulation of Temperature Field in Friction Stir Welding

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Xiangqian Liu ◽  
Yan Yu ◽  
Shengli Yang ◽  
Huijie Liu
Keyword(s):  
Heat Flux ◽  
Friction Stir Welding ◽  
Analytical Model ◽  
Heat Generation ◽  
Tilt Angle ◽  
Temperature Fields ◽  
Analytical Models ◽  
Maximum Temperature ◽  
Thermal Cycles ◽  
Friction Stir

In the conventional analytical model used for heat generation in friction stir welding (FSW), the heat generated at the pin/workpiece interface is assumed to distribute uniformly in the pin volume, and the heat flux is applied as volume heat. Besides, the tilt angle of the tool is assumed to be zero for simplicity. These assumptions bring about simulating deviation to some extent. To better understand the physical nature of heat generation, a modified analytical model, in which the nonuniform volumetric heat flux and the tilt angle of the tool were considered, was developed. Two analytical models are then implemented in the FEM software to analyze the temperature fields in the plunge and traverse stage during FSW of AA6005A-T6 aluminum hollow extrusions. The temperature distributions including the maximum temperature and heating rate between the two models are different. The thermal cycles in different zones further revealed that the peak temperature and temperature gradient are very different in the high-temperature region. Comparison shows that the modified analytical model is accurate enough for predicting the thermal cycles and peak temperatures, and the corresponding simulating precision is higher than that of the conventional analytical model.

scholarly journals Acoustic Target Strength of the Endangered Chinese Sturgeon (Acipenser sinensis) by Ex Situ Measurements and Theoretical Calculations

2018 ◽  
Vol 8 (12) ◽  
pp. 2554 ◽  
Author(s):  
Hui Zhang ◽  
Junyi Li ◽  
Chongrui Wang ◽  
Chengyou Wang ◽  
Jinming Wu ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Breeding Population ◽  
Ex Situ ◽  
Target Strength ◽  
Effective Management ◽  
Chinese Sturgeon ◽  
Acipenser Sinensis ◽  
Acoustic Target ◽  
The Mean ◽  
Db Difference

The Chinese sturgeon, Acipenser sinensis, is a large anadromous and highly endangered protected species. The assessment of its breeding population in the Yangtze River is critically important for effective management and population preservation. Currently, hydroacoustic methods have been widely used to study the adult sturgeons in the river, whereas the acoustic target strength (TS) characteristics of the species have not been studied. In this study, the TS of Chinese sturgeon was carefully evaluated both by ex situ measurements and theoretical calculations. Six Chinese sturgeons (Body Length (BL): 74.0−92.6 cm) were measured by a 199 kHz split echosounder in a 10-m deep net cage. The computed tomography of a Chinese sturgeon (BL: 110.0 cm) was conducted and the Kirchhoff ray mode (KRM) method was used to estimate the theoretical TS. As a result, the mean ex situ TS range of the six specimens was from −26.9 to −31.4 dB, which was very close to the KRM estimation (~1 dB difference). Then, the KRM method was used to predict the TS of Chinese sturgeon as a function of BL in six frequencies commonly used in freshwater environments and to estimate the TS of a representative adult Chinese sturgeon (250 cm) as a function of frequency and tilt angle. This study can provide a good basis for future hydroacoustic studies on the critically endangered Chinese sturgeon.

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