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1
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Shipping Low Frequency Noise and Its Propagation in Shallow Water

100%
Kozaczka E., Grelowska G.
Acta Physica Polonica A
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2011
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vol. 119
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issue 6A
1009-1012
EN
One of the most significant factor influencing acoustical climate of the sea is underwater noise generated by moving ships. If the considered sea area has features of the shallow water, namely the wave frequency fulfils relation f < 10c/h, where c denotes phase speed of sound, and h is depths of the sea, then in certain distance from the wave source specific image of sound pressure distribution in the mean of wave modes appears. The modes constitute wave packet propagating with group speed in the direction parallel to the sea surface. The paper presents results of the experimental investigation concerning the distribution of the sound field created by moving ship in the shallow water, in a small distance from the ship. The main acoustical characteristics, describing features of the field are spectrograms in pseudo-3D system: distance and frequency in geometrical form, and sound intensity in the optical one (color). Results presented in such a way pointed individual features of the sound source known often as acoustical signature of the source (ship).
2
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Sounding of Layered Marine Bottom - Model Investigations

100%
Grelowska G., Kozaczka E.
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EN
The necessary actions connected with interpretations of examining of physical properties of sea bottom structure is developing of proper procedure of modeling of the layered structure. The implementation of the acoustic waves for the determination of seabed stratification requires a precise diagnosis of the topic from both the theoretical and practical side. Little differences between the parameters of sediments, as well as irregular distance between layers make the interpretation of the images of cross sections uneasy. The paper presents the model of stratified structure of seabed in the form of a liquid on which falls the perpendicular elastic wave. Since the description of the seabed is made on the basis of reflected impulse shape, which provides the information about the structure and material properties such as density and speed of wave propagation, the important role among other things has the spatial resolution, because the pulse length determines the possibility of distinguishing between the layers. These aspects require very careful analysis of the form of reflected signals.
3
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Images of the Seabed of the Gulf of Gdańsk Obtained by Means of the Parametric Sonar

81%
Kozaczka E., Grelowska G., Kozaczka S.
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issue 1
91-94
EN
The main goal of this paper is to present results of the experimental investigation of the seabed by means of parametric echosounder in the form of chosen images. The phenomena of nonlinear interaction between two parallel beams of high intensity gives as a results very narrow beam of low frequency wave, that enables to penetrate the sea bottom. The first step of our investigations was calibration of all the elements of the measuring system. In the second step the marine trials were carried out. For this purpose the mobile measuring set up was installed on the board of sailing boat. The details about the measuring devices can be found below. The main goal of these investigations was to determine the structure of the seabed for different places of the Gulf of Gdańsk. The special features of parametric generation of sound beam allow to penetrate the bottom for more then several meters. At the end of the paper, a set of images that illustrated the results of investigations has been presented.
4
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The Examination of the Upper Layers of the Seabed by the Means of the Acoustic Methods

81%
Kozaczka E., Grelowska G., Szymczak W., Kozaczka S.
Acta Physica Polonica A
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2011
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vol. 119
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issue 6A
1091-1094
EN
Propagation of acoustic waves in the sea, in particular in shallow sea, depends on several factors. The basic of them are source power and frequency of acoustic waves, spatial distribution inhomogeneous medium in which acoustic wave propagates, and distributions of speed of sound and density of seawater. The coastal conditions, which limit water medium from above (free surface of the sea) and from bottom (the seabed), are no less important. In this paper we will consider the examination of the layer structure of the seabed by the means of the acoustic methods. By the notion of acoustic methods we mean use of phenomena in the field of nonlinear hydroacoustics. Based on this, the parametric sonar was constructed and was used to the seabed sounding. This parametric sonar is commonly called sub-bottom profiler. The selected results of extensive experimental research, that have been performed in waters of the Gulf of Gdańsk in the years 2008-2010, will be presented in this work.
5
Content available remote

Diver Observations by Means of Acoustic Methods

81%
Kozaczka E., Grelowska G., Kozaczka S., Szymczak W.
Acta Physica Polonica A
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2013
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vol. 123
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issue 6
1098-1100
EN
Searching for objects, especially small ones, moving under water near its the free surface, is always not an easy task. Designing tools for the detection of such targets is a real challenge when the possibility of a terrorist attack is a real threat. This paper presents some aspects of diver detection by means of acoustics methods, both active (side scan sonar) and passive ones (linear receiving antenna). This approach is quite effective because divers can use both breathing apparatus operating in the closed-loop (so-called rebreathers), and popular open-circuit breathing (exhalation of used air or a breathing gas mixture into the water).
6
Content available remote

Investigation of Transmit and Receive Characteristics of Laboratory Model for the Parametric Echosounder

61%
Grelowska G., Kozaczka E., Nowicki A., Kozaczka S., Szymczak W., Tymkiewicz R.
Acta Physica Polonica A
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2013
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vol. 123
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issue 6
1094-1097
EN
Investigation and operation of devices based on nonlinear interaction of high-intensity waves have been carried out for several decades. However, it is still a new tool to study the properties of the water environment and especially the upper layers of the seabed. This paper describes the results of tests of the new device that is intended to be applied for sounding underwater areas. The device has been designed and built in collaboration with the Department of Ultrasound of the Institute of Fundamental Scientific Researches of the Polish Academy of Sciences in Warsaw.
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