• The Journal of the Acoustical Society of Korea
• /
• v.21 no.3
• /
• pp.213-220
• /
• 2002

The sound wave in the sea propagates under the effect of water depth, sound velocity structure, sea surface and bottom roughness, and bottom sediment distribution. In particular the sound velocity structure in shallow water varies with time and space, an? the sediment distributes very variedly with place. In order to investigate the seasonal variation of low-frequency sound propagation in the Yellow Sea, the propagation experiments were conducted along the same track in the middle part of the Yellow Sea at various seasons of spring. summer, and autumn. In this paper we consider the measurement results on the propagation loss with the sound velocity structure, and investigate the seasonal variation of the propagation loss. As a result, the propagation losses measured in summer were larger than the losses in spring and autumn. And the propagation losses measured in autumn were smaller than the losses in spring. The seasonal change of the propagation loss increased with the rise of sound frequency and the propagation range.

• Journal of Advanced Marine Engineering and Technology
• /
• v.34 no.8
• /
• pp.1222-1229
• /
• 2010

Compared to conventional high resolution acoustic profiling, ultra high resolution shallow acoustic profiling using parametric echo sounder is limited in penetration, yet it provides resolution suitable for detailed seabed investigation in the shallow waters. The parametric sub-bottom profiler system provides not only the exact determination of water depth, but also the detailed information about sediment layers and sub-bottom structures. Possible applications include dredging project, search of buried pipeline, ship wrecks, and other artificial objects through the detailed mapping of thickness and structure of the upper sedimentary layers. In this study, contaminated sediments were discriminated by the correlation of ultra high resolution profiles with geologic data. In addition, the burial depth of the submarine cable was measured by the interpretation of acoustic anomalies in the profiles.

• The Journal of the Acoustical Society of Korea
• /
• v.32 no.6
• /
• pp.455-471
• /
• 2013

Active sonar has been commonly used to detect targets existing in the shallow water. When a signal is transmitted and returned back from a target, it has been distorted by various properties of acoustic channel such as multipath arrivals, scattering from rough sea surface and ocean bottom, and refraction by sound speed structure, which makes target detection difficult. It is therefore necessary to consider these channel properties in the target signal simulation in operational performance system of active sonar. In this paper, a monostatic active sonar system is considered, and the target echo, reverberation, and ambient noise are individually simulated as a function of time, and finally summed to simulate a total received signal. A 3-dimensional highlight model, which can reflect the target features including the shape, position, and azimuthal and elevation angles, has been applied to each multipath pair between source and target to simulate the target echo signal. The results are finally compared to those obtained by the algorithm in which only direct path is considered in target signal simulation.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2008.10a
• /
• pp.79-84
• /
• 2008

Compared to conventional high resolution acoustic profiling, ultra high resolution shallow acoustic profiling is limited in penetration, yet it provides resolution suitable for detailed seabed investigation in the shallow waters. Possible applications include search of buried pipeline, ship wrecks, and other artificial objects through the detailed mapping of thickness and structure of the upper sedimentary layers. In this study, contaminated sediments were discriminated by the correlation of ultra high resolution profiles with geologic data. In addition, the burial depth of submarine cable was measured by the interpretation of acoustic anomalies in the profiles.

• The Journal of the Acoustical Society of Korea
• /
• v.14 no.2E
• /
• pp.57-64
• /
• 1995

In this study, we examine the applicability of the classifier based on an artifical neural network (ANN) for the low-frequency acoustic signal in shallow water environment. The estimations of the Doppler shift and frequency spreading effect at 220 Hz reveal the frequency variation of less than 2 Hz with time This small variation enables the ANN-based classifier to identify signals using only tonal frequency information. The ANN consists of 4 layers, and has 60 input processing elements (PEs) and 4 output PEs, respectively. When measured tonal signals in the frequency 200-250 Hz are applied to the ANN-based classifier, the classifier can identify more than 67% of the signals for instantaneous frame and more than 91% for averaged one over 5 frames.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.34 no.6
• /
• pp.661-665
• /
• 2001

This paper deals with optimal mooring system to secure fish cage in a desired location, Through field investigation and paper works, we surveyed disasters by breakdown of cage frame and mooring system due to higher wave attack and selected compliant buoy mooring method for shallow water mooring system against severe coastal external forces. To analyze interaction between external forces and compliant buoy mooring system, theoretical model has developed as quasi-static nonlinear analysis. After verifying the feasibility of the numerical model compared with experiment, static analysis has tried for various mooring systems with different angle of array, number of mooring points, length of horizontal and inclined rope. Optimal mooring method using compliant buoy has selected for fish cage through numerical simulation. This results can apply for preliminary design for cage mooring system.

• Journal of Navigation and Port Research
• /
• v.27 no.1
• /
• pp.87-95
• /
• 2003

Submarine optical fiber cable construction consists of marine survey, PLGR(Pre Lay Grapnel Run), shore-end-work, laying the submarine optical cable. This PLGR is work to ease the cable lay safely in seabed, improve the performance of Plough and ROV (Remotely-Operated Vehicle) laying work, and protect laying equipment. This paper presents the design and implementation of real-time monitoring system for PLGR work in submarine optical fiber cable construction enterprise. In this paper, we designe overall real-time monitoring system. For this purpose, the modules such as serial multiport communication module, real-time processing module, environment configuration module, real-time graph and a printout modules are designed and implemented. For the validity evaluation of this paper, serial multi port communication module, data parsing, realtime graph output are implemented and tested.

• The Journal of the Acoustical Society of Korea
• /
• v.35 no.6
• /
• pp.419-426
• /
• 2016

Measurements of bottom loss as a function of grazing angle (in range of $9{\sim}14^{\circ}$) at a frequency range of 4 ~ 8 kHz were conducted on an experimental site off Geoje island in October 2015. Geoacoustic inversion of the surficial sediment thickness is performed using the arrival time difference between the surficial layer and the sub-bottom layer reflected signal. To invert the thickness of surficial sediment, we used the grain size of $8{\sim}10{\phi}$ obtained by KIGAM (Korea Institute of Geoscience and Mineral Resources). The thickness of the surficial sediment was estimated to be 4 ~ 7 m. Finally, this inversion result was compared with the geoacoustic observation conducted by the KIOST (Korea Institute of Ocean Science & Technology) using sub-bottom profiler.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.24 no.3
• /
• pp.405-411
• /
• 2020

Recently, studies on underwater communication, related to the development of underwater resources, disaster monitoring and defense, have been actively carried out. In the design of wireless communication systems, path loss is the most important information to derive a link budget that is required to guarantee communication reliability by calculating received power level for the given communication link. The underwater acoustic channel have different characteristics according to geographical location and relevant environmental factors such as water temperature, depth, wave height, algae, and turbidity. Subsequently, many research institutes aiming to develop underwater acoustic communication systems are researching actively on the underwater acoustic channels in various sea areas. In Korea, however, studies on the path loss of the acoustic channel are still insufficient. Therefore, in this study, the path loss of the acoustic channel are studied based on measurement data of the at-sea experiment conducted at Geohae-do, southern sea of Korea.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.26 no.3
• /
• pp.436-442
• /
• 2022

In this paper, the performance of the selective combining according to the channel selection decision method of frequency diversity is evaluated in the underwater frequency selective channel. The underwater acoustic channel in the shallow sea has a complex multipath characteristic by combining various environmental factors such as boundary surface reflection and sound wave refraction according to the water temperature layer. In particular, frequency selectivity due to multipath causes energy fluctuation in a communication channel, which reduces SNR (Signal to Noise Ratio) and deteriorates communication performance. In this paper, we applied the frequency diversity technique using multiple channels to secure the communication performance according to the frequency selectivity by multipath. For each channel, 4-FSK (Frequency Shift Keying) and selective combining were applied, the performance was evaluated by applying the maximum value, average value, and majority decision of the signal in order to decide the demodulation channel selection of the selective combining.