Essay Example on Underwater acoustics signal is the study of the Propagation

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Abstract Underwater acoustics signal is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water and its boundaries The water may be in the dam ocean a lake or a tank There are some frequencies affiliated with underwater acoustics are between 10 Hz and 1 MHz There are some major steps for underwater signal de noising The first step deals with signal preprocessing which including amplifying filtering and take use of analogy digital AD technique to save signals as digital file The underwater acoustic signal is affected by ocean interference and ambient noise disturbance during its propagation in ocean Acoustic waves are the most important characteristic to convey data in underwater domain as a practical method But the oceans are increasingly exposed to sounds from human activities such as shipping and the building of foundations for offshore construction projects and other different noise Keyword underwater acoustic signal wavelet transform signal processing denoising noise reduction 



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1 Introduction Because of the activities of people in the ocean are expanded the field of underwater acoustics has been extensively developed in a variety of applications including acoustic communication the detection and location of surface and subsurface objects depth sounders and sub bottom profiling for seismic exploration l underwater acoustic signals that received from ocean are the signal of ships radiated when it sails on the ocean The aim of this paper is to develop a de noising system and evaluate the effect of wavelet de noising processing for underwater acoustic signals Noise hampers sonar data collection and related processing of the data to extract information since many of the signals of interest are of short duration and of relatively low energy Underwater signal transmission is a challenging task since the usable frequency range is limited to low frequency and the transmission of electromagnetic waves is impossible due to its high attenuation nature The types of attenuation that affects the sound signal are transmission loss Spreading Loss Attenuation Loss Background noise like Self Noise Machinery Noise Flow Noise etc 1 1 Motivation Human interaction is the study in underwater acoustic signal which is the rapidly growing topic everywhere Communication purpose Commercial Warship Acoustic communications form an active field of research with significant challenges to overcome especially in horizontal shallow water channels 1 2 Objective Reduce noise in underwater for acoustic signal Sound propagation losses Self noise and ambient noise SNR Mixed Gaussian noise 



2 Literature review A noise removal algorithm based on short time Wiener filtering is described An analysis of the performance of the filter in terms of processing gain mean square error and signal distortion is presented Noise hampers sonar data collection and related processing of the data to extract information since many of the signals of interest are of short duration and of relatively low energy 1 The evaluation is performed on a representative real data set of underwater acoustic records Rationales used to process the proposed evaluation are mean squared error global signal to noise ratio SNR segmental SNR and mean squared spectral error These filters are generally designed by a calculation which involves the signal autocorrelation estimation a difficult task in case of low SNR or presence of non stationary components Musical noise is a perceptual phenomenon that occurs when isolated peaks remain in the time frequency representation after processing with spectral subtraction algorithm 2 The authors S S Murugan et al 3 studied the real time data collected from the Bay of Bengal at Chennai by implementing Welch Barlett and Blackman estimation methods and improved the maximum Signal to Noise Ratio to 42 51 dB The authors Yen Hsiang Chen et al 4 implemented a real time adaptive wiener filter with two microphones is implemented to reduce noisy speech when noise signals and desired speech are incoming simultaneously Sound travels rapidly through water four times faster than the air As in open air sounds are transmitted in water as a pressure wave They can be loud or soft high or low pitched constant or intermittent and volume decreases with increasing distance from source Sound pressure is most commonly measured in decibels dB


Underwater noise has been divided into two main types Impulsive Loud intermittent or infrequent noises such as those generated by piling and seismic surveys Continuous Lower level constant noises such as those generated by shipping and wind turbines These two types of MSFD related noise have different impacts on marine life In addition mid frequency naval sonar may be harmful to marine mammals The frequency or pitch of the noise is also important as animals are sensitive to different frequencies 

5 The underwater acoustic signal is affected by ocean interference and ambient noise disturbance during its propagation in ocean Therefore the signal reveal random process and time varying characteristics The procedure consists of three parts First wavelet transformation of the underwater acoustic signals Secondly threshold of wavelet coefficients Thirdly inverse wavelet transformation of reconstructing modified signals 6 Because of the activities of people in the ocean are expanded the field of underwater acoustics has been extensively developed in a variety of applications including acoustic communication the detection and location of surface and subsurface objects depth sounders and sub bottom profiling for seismic exploration 7 The Ultrasonic signal is most commonly used for the depth estimation This signal is affected by various underwater noises which results in inaccurate depth estimation The objective of this paper is to provide noise reduction methods for underwater acoustic signal In present work the signal processing is done on the data collected using TC2122 dual frequency transducer along with the Navy sound 415 echo sounder There are two signal processing techniques which are used The first method is denoising algorithm based on Stationary wavelet transform SWT


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