38 research outputs found
Experimental evidence of horizontal refraction by non-linear internal waves of elevation in shallow water in the South China Sea: 3D vs. Nx2D acoustic propagation modeling
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Three-dimensional acoustic simulation of an acoustic refraction by a nonlinear internal wave in a wedge bathymetry
No full textUncertainty analysis of acoustical normal incidence reflection from seabed
No full textnderwater acoustic technology is widely used in marine resources exploration, air crash survey and shipwreck, even underwater archaeology is included. Sub-bottom profiler is one of the system to measure marine geology. To find the uncertainty of reflection coefficient by useing this set of system. We use the acoustical sub-bottom profiler made by our lab and focus on verifying two assumptions from reflection of the coefficient formula. First of all, analysis of the sound pressure transmission loss in the water layer which affected by the change of hydrology environmental. Then, verifying the sound pressure reflection at the sea surface is the total reflection. The experiments carried out in the waters southwest of Taiwan and the South China Sea. According to the experimental results, identifying the uncertainty of sound pressure loss over distance, and quantify this uncertainty results to apply in the calculation of the reflection coefficients. And provide reflection coefficient correction value from water reflection. Enhance calculations accuracy with two echo to calculate the reflection coefficient. The two correction will be verify by seabed sampling and videos and provide a reference to scholars who study marine sediments
Developing Sonar System Using Beamforming for Target Detection in Harbor Environment
No full textHarbor defense not only must be improved but should react to the rapid demand from the unconventional terrorist attack. In this paper, an underwater autonomous transmitting and recording system was designed to detect unknown underwater target at port, an extremely shallow environment.
The ability to apply these techniques using modern embedded computer both hardware and software is illustrated by a case study on the design of a versatile platform for both the transmitting and recording of underwater acoustic signals, which includes detail watertight compartment design, hardware integration, system construction and power supply configuration.
The paper aims to find a new method to detect the underwater target in harbor. In April 2, 2019, an active sonar experiment, which used a transmitter to generate signal to a 3-channel recording array to collect the echo from the target, was conducted at Kaohsiung Port (first harbor). The result shows that the system successfully achieve the goal. Not only we can notice the target by noise which produced by the target (ship), but echo which reflected by the opposite bank as well. The echo from the opposite bank only occurs when no targets remains or pass by. In other words, when the target passes the first harbor, the target will block the experimental signal which makes the echo from the opposite bank disappear. In order to grasp the target movement further, we comprehend the relative angle between the target and the experimental system by using beamforming algorithm. With the delay time and the angle of continuous target echo, the speed and relative location of the target is known as well.
To sum up, an autonomous acoustic system, which successfully detects target moving vehicle in Kaohsiung First Port, is built in this study. Through the shading observation of the echo from opposite side of the port, the moving vehicle can be successfully detected. Via beamforming, the angle of the echo from the moving vehicle and its moving speed are known. Despite this system is designed for target detection, with different usage or analysis, it can also be a set source or receiver on a mooring in future
Analysis and Comparison of Same Period in Summer on Ocean Ambient Noise of Taiwan Southeastern and Northeastern Seas
No full textWhen communications or detection in the ocean, sonar system is the main tool for signal transmission and ocean ambient noise is one of the important parameters in it. Ocean ambient noise includes various and diverse sources like wind, rain, marine life, ship, and etc. Using different ways to analyze are needed to understand the complicated properties of ocean ambient noise, therefore sonar system performance prediction can be improved significantly. In this study , the ocean ambient noise data were collected in summer of 2012 at Taiwan southeastern and northeastern seas, then analyzed and compared the characteristics and divergence of wind-wave and rain- generated noises of same period , and plot wind-wave and rain- generated spectrum to compare noise level in different frequency and sea states at different seas. Finally, calculated the high frequency(>0.5 kHz) noise energy budgets of wind-wave and rain generated. Furthermore, using residual analysis to select good data of noise and wind speed before data processing, when the good data meet the assumptions of linear regression, then the wind-wave noise prediction equations from can be obtained. The estimation and measurement of noise level were compared to verify the equations are accurate. In low frequency (<0.5 kHz), ambient noise has periodic peak shown in spectrum, the noise level increases 10 to 15 dB every 24 hours. By using sea level and temperature data, the periodic fluctuation of low frequency sound level is proved to be related to the tidal current
