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Compared with Fourier transformation and the wavelet packet decomposition, empirical mode decomposition has the best adaptability. It can also provide higher frequency resolution. Empirical mode decomposition can be applied to the field of signal detection and signal features extraction, and it is able to find subtle changes in the signals. There is huge potentiality for using the method in weak signal...
In sound fields, the incident wave and the reflected wave are superimposed together; but sometimes we need to isolate the sound waves. In this paper, we present two methods of isolating the incident wave and the reflected wave in the sound fields, the two methods are: the double-pressure sensor method; and, the pressure-velocity sensor method. The double-pressure sensor method involves obtaining the...
Seamounts in deep water have significant effects on the sound propagation. However, the reconstruction of the broadband pulses behind a seamount is indeed challenging due to the complex environment. It seems worthy to investigate the effects of seamounts on sound propagation in deep water. An experiment was conducted in 2014 in the Southern China Sea to investigate sound propagation in an environment...
In this paper, we intend to quantify the dynamical complexity ofunderwater acoustical signals (UAS) based on multiscale sample entropy (MSE). MSE is calculated for three types of UAS which were measured in the South China Sea: ambient noise, and near and distant experimental vessels moving at constant velocity. [The analysis of real UAS exhibit high entropy values were assigned for ambient noise and...
Study on the frequency dispersion curve of elastic cylindrical shells is the foundation of nondestructive testing and target recognition. The traditional calculation method for frequency dispersion curves is based on thin shell theory and ‘Regge track’, which is beset by low computational efficiency. The spectral method is regarded as a novel approach of solving ordinary or partial differential equations...
Low-frequency active acoustic detection of underwater targets is of much interest both at home and abroad. The scattering field of targets is uniquely determined by its structural surface impedance, sound radiation impedance and acoustic load. Because the internal structure of targets and their surface coatings are usually extremely complicated, computations in numerical simulations are time consuming...
This paper presents a method to identify the noise radiation regions of an acoustic source from a small number of measurement points. First, the acoustic radiation modes that contribute to the acoustic far-field are selected. Next, the velocities on the surface of the acoustic source are reconstructed based on the selected acoustic radiation modes. Finally, the noise radiation regions are determined...
The theoretical analyses of the vibroacoustic behavior of an infinite double-leaf partition consisting of vacuum-partition-gas-partition'-water are conducted. For comparison, those of an infinite single-leaf partition consisting of vacuum-partition-water are also accomplished. Both the vibration of partitions and the acoustic transmission in gas and water are taken into consideration. The two systems...
In order to demodulate an underwater acoustic signal detected by a fiber-optic hydrophone system, some different demodulation principles are proposed for study. Of all the principles, PGC (phase generated carrier) technology is more and more commonly used in a fiber-optic Michelson hydrophone system at present. In this paper, through SIMULINK and LABVIEW simulation, a mono-frequency signal, a double-frequency...
Ambient noise in the ocean has been measured and studied for over half a century. Due to multipath effects, the signal will not always arrive from the horizontal direction. The directional response of a vertical line array (VLA) to a distant source can be expressed in terms of the modal beams weighted by their normal mode amplitudes. This modal representation offers a physical interpretation of the...
On account of the complex underwater acoustic channel with severe attenuation, multipath effect, Doppler effect, as well as time and frequency spread characteristics, the task of inferring modulation of the underwater acoustic communication signals is extremely difficult and challenging. In this paper, we propose an automatic modulation recognition (AMR) scheme in order to recognize the MPSK signals...
This paper proposes a method of extracting transient signals in the presence of colored noise using an adaptive line enhancer. Transient signals are non-stationary signals with a shorter duration than the observation interval. The problem of transient signal extraction arises in many fields of application - for instance, in mechanical failure diagnostics and in underwater acoustic warfare - where...
In the simulation of underwater acoustic propagation, sound speed is usually characterized by the vertical distribution of the sound speed profile (SSP), but it ignores lateral variation. This paper carried out simulation on constant SSP, negative and positive gradient profile, and real sound speed profiles (SSPs), concerning a Gulf Stream scenario, and by using Bellhop model. The characteristics...
This paper describes an iterative, efficient, and use-case driven UML object modeling method used in the process of software development of an ocean parameters measurement system. The method solved all kinds of complex issues (complex related factor), variety (variety of equipment and data types), and frequent changes in the software development of an ocean parameters measurement system.
Long Baseline (LBL) positioning is an important and high-precision method for underwater vehicle navigation. It has the highest accuracy among all the acoustic positioning methods. LBL positioning system use one-way-travel-time measured between target and beacons, which is the raw data of measured values. But there are some problems in travel-time measurements: firstly, due to other signal interferences...
The hydrophone calibration system in a small water tank has broad application prospects. This paper studies some theory evidence of the practicability of the hydrophone calibration system in a small water tank. Simulation of the sound field in a small water tank shows the distribution of the acoustic field there in. An experiment is conducted to compare a vector hydrophone with a standard hydrophone,...
Far-field beam-forming is applied in the detection system of large-aperture optical towed linear arrays to estimate the direction of targets. Actually, for a large-aperture line array, multiple targets are located in near-field. In these circumstances, if we still use far-field beam-forming for approximate processing, it will cause bearing-amplitude distortion which seriously influences the precision...
Underwater acoustic sensor networks (UASN) are a promising research area, due to the wide range of aquatic applications, such as pollution monitoring and submarine detection. The realistic evaluation of the novel UASN protocols and algorithms in the field trials is too expensive and time-consuming. Therefore, standard simulation and emulation platforms of UASN are quite required, and can efficiently...
For detecting the transient signal with low SNR, such as water entry sound, the WP-Page Test is proposed in this paper, basing on the traditional Page Test detector. The Page Test is a common method used in change detection. However, it usually cannot meet the requirement because of the low SNR in actual detection. The WP-Page Test detector is use wavelet packet analysis in order to improve the SNR...
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