• Korean Journal of Fisheries and Aquatic Sciences
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• v.52 no.6
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• pp.709-718
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• 2019

Cephalopods, such as the Japanese flying squid Todarodes pacificus and golden cuttlefish Sepia esculenta, are an important food source for all toothed whales, particularly bottlenose dolphins in costal and offshore waters around the Korean Peninsula. A controlled laboratory experiment was conducted to investigate the broadband acoustic backscattering from live individuals of these two cephalopod species using linear chirp signals (100-200 kHz). The backscattered echo signal was measured at about 1° intervals from -45° (head down) to +45° (head up) in the dorsal plane. The species-specific, frequency-dependent scattering characteristics were investigated by comparing the relationship between the wavelength-normalized backscattering cross-section (σ/λ²) and the wavelength-normalized fish length L/λ for each species. The estimated σ/λ² value for Japanese flying squid was 9.51 at an L/λ range of 12.79-30.27 (mean, 21.26). This was approximately 7% of the σ/λ² value (136.1) for golden cuttlefish at an L/λ range of 9.07-25.49 (mean, 15.77).

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.spc
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• pp.18-22
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• 2022

Because it is difficult to apply direct and optical detection techniques to sunken hazardous and noxious substances (HNS), effective acoustic detection techniques are required to detect sunken HNS in water. In this study, the possibility of acoustic detection of sunken HNS was investigated through backscattering signal measurement experiments using chloroform, a sunken HNS. After establishing a pool in an acrylic tank, backscattering signals were measured according to the presences or absence of chloroform by varying the grazing angle from 90° to 50° in 0.5° intervals using a pan&tilt system. A directional transducer transmitted and received sinusoidal signals with a frequency of 200 kHz and a pulse length of 25 ㎲ in a monostatic state. When chloroform was deposited, the received level of the backscattering signal at the interface between water and chloroform became low at a grazing angle of approximately 80° or smaller. Based on the backscattering signal results obtained at the interface between water and chloroform, the possibility of acoustic detection of sunken HNS was demonstrated.

• The Journal of the Acoustical Society of Korea
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• v.31 no.4
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• pp.205-213
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• 2012

Active acoustic array signal was measured in the East Sea and the South sea and spatial coherence was analyzed. The measurement of ambient noise, target reflection signal, sea surface backscattering signals took place including environmental measurements of sea wind, and vertical temperature profiles. The spatial coherence of ambient noise was lower than that of target reflection signal in the South Sea. The spatial coherence of target reflection signal was above 0.5 over all array length. The spatial coherence of sea surface backscattering signal was higher in high incident angle. The maximum non-dimensional array length was 3.0 ($26^{\circ}$) and 3.5 ($32^{\circ}$) to have spatial coherence above 0.5 in the East Sea. To find a design criteria for array configuration and array performance, more measurements of temporal and spatial coherence will be needed continuously in the future.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.2
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• pp.163-168
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• 1989

In this paper, Rayleigh wave velocity has been measured by detecting the backscattered signal generating near the Rayleigh critical angle in the elastic medium. The rotating system has been made for the measurment of Rayleigh angle. It has been shown that the measured velocity for the stainless steel, brass aluminum, copper has been good agreement with the theoretical value. The method of non-destructive evaluation using backscattering signal has been presented and the c-scan acoustic image for internal of IC sample has been displayed.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.47-50
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• 1988

In this paper, Rayleigh wave velocity has been measured by detecting the backscattered signal generating near the Rayleigh critical angle in the elastic medium. The rotating system has been made for the measurment of Rayleigh angle. It has been shown that the measured results has been good agreement with the theoretical value. The method of non-destructive evaluation using backscattering signal has been presented and the internal of IC sample has been displayed acoustic image with good contrast.

• The Journal of the Acoustical Society of Korea
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• v.21 no.4
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• pp.421-429
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• 2002

Sea surface backscattering signal measurements were conducted in the shallow waters off the east coast of Korea to study the acoustic wave scattering from the sea surface. The grazing angles of wave range from 20° to 40° with a frequency of 60 kHz. The wind speed and surface roughness of the experiment area were 3 m/os and below 1 m, respectively. The measured acoustic backscattering strengths greatly exceed the composite roughness predictions at low grazing angles. To account for this discrepancy, the scattering strengths due to a near-surface bubble layer were considered. The prediction with bubble contribution was found to be in good agreement with the experimental measurement.

• The Journal of the Acoustical Society of Korea
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• v.23 no.8
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• pp.562-569
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• 2004

An experiment for observation of the distribution of the seagrass (zostera marina) beds and characteristics of high-frequency backscattering by the photosynthesis was conducted off the coast. Acoustic data were taken as a function of the grazing angles and the relative azimuth angles on the seagrass beds of which bottom type was sandy-mud. The transmitted source signal was a 120 kHz CW waveform. Mapping of the seagrass beds distribution was drawn up using the seagrass backscattering strength with azimuth and grazing angles. The result of the comparison backscattering strength distribution of the seagrass beds was shown to be the similar to the photograph of real seagrass beds. The seagrass backscattering strength was also compared between day and night to verify the effects of the acoustical scattering by the bubbles of Photosynthetic oxygen formed on the seagrass. In these results. it is clear that observation of the seagrass beds between day and night showed the different characteristics because the bubbles of Photosynthetic oxygen affect the acoustical scattering.

• 한국해양학회지
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• v.22 no.3
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• pp.143-152
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• 1987

The digital data were obtained using Kennedy 9000 magnetic tape deck which was connected to the SMS960 side scan sonar during the field operations. The data of three consecutive survey tracks near Seongsan-po, Cheju were used for the development of this study. The softwares were mainly written in Fortran-77 using VAX 11/780 MINI-COMPUTER (CPU Memory; 4MB). The established mapping system consists of the pretreatment and the digital processing of seafloor image data. The pretreatment was necessary because the raw digital data format of the field magnetic tapes was not compatible to the VAX system. Therefore the raw data were read by the personal computer using the Assembler language and the data format was converted to IBM compatible, and next data were communicated to the VAX system. The digital processing includes geometrical correction for slant range, statistical analysis and cartography of the seafloor image. The sound speed in the water column was assumed 1,500 m/sec for the slant range correction and the moving average method was used for the signal trace smoothing. Histograms and cumulative curves were established for the statistical analysis, that was purposed to classify the backscattering strength from the sea-bottom. The seafloor image was displayed on the color screen of the TEKTRONIX 4113B terminal. According to the brief interpretation of the result image map, rocky and sedimentary bottoms were very well discriminated. Also it was shown that the backscattered acoustic pressurecorrelateswith the grain size and sorting of surface sediments.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.52 no.4
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• pp.318-324
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• 2016

Commercial split beam echosounder (ES70) installed on a krill fishing vessel was calibrated in order to utilize it in estimating biomass of Antarctic krill (Euphausia superba). The method of calibration was to analyze the difference between the bottom backscattering strength of the commercial split beam echosounder (i.e. ES70) and the scientific echosounder (i.e. EK60) at one of transects near South Shetland Islands designated by CCAMLR. 38 kHz and 120 kHz were used for the calibration, and krill swarm signal levels obtained from multi frequencies, was examined to verify the calibration result. The analysis result indicated possibility of calibration by bottom backscattering strength, since the proportion of krill swarm signals within 2 dB < $S_{V\;120\;kHz-38\;kHz}$ < 12 dB (i.e. a common $S_{V\;120\;kHz-38\;kHz}$ range of 38 kHz and 120 kHz to be an indicator of Antarctic krill) over the total acoustic signals were 26.95% and 92.04%, respectively before and after the calibration.

• Ocean and Polar Research
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• v.35 no.1
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• pp.15-26
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• 2013

The toxic, Harmful Algal Blooms (HABs) caused by the Cochlodinium polykrikoides have a serious impact on the coastal waters of Korea. In this study, the acoustic detection system was developed for rapid HABs detection, based on the acoustic backscattering properties of the C. polykrikoides. The developed system was mainly composed of a pulser-receiver board, a signal processor board, a control board, a network board, a power board, ultrasonic sensors (3.5 and 5.0 MHz), an environmental sensor, GPS, and a land-based control unit. To evaluate the performance of the system, a trail was done at a laboratory, and two in situ trials were conducted: (1) when there was no red tide, and (2) when there was red tide. In the laboratory evaluation, the system performed well in accordance with the number of C. polykrikoides in the received level. Second, under the condition when there was no red tide in the field, there was a good correlation between the acoustic data and sampling data. Finally, under the condition when there was red tide in the field, the system successfully worked at various densities in accordance with the number of C. polykrikoides, and the results corresponded with the sampling data and monitoring result of NFRDI (National Fisheries Research & Development Institute). From the laboratory and field evaluations, the developed acoustic detection system for early detecting HABs has demonstrated that it could be a significant system to monitor the occurrence of HABs in coastal regions.