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System for bistatic measurements of reverberations in the shallow sea area

Klusek Z., Elminowicz A., Majewski P., Dragan A.

Hydroacoustics

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2011

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Vol. 14

83-90

EN

In the paper a system for measurements of reverberations in the shallow sea environment is presented. The setup operated in 40–80 kHz frequency range with pseudomonochromatic pulses or chirp signal and has possibility to acquire bistatic scattered data. The system is constructed in such manner that depending on an experiment configuration we could perform measurements of the local 3D scattering strength of the bottom and/or far range bistatic reverberations from the sea surface, volume inhomogeneities and sea bottom. The final objective of the system is to give prognosis for probability of target detections when using bior multistatic barriers. Details of the individual blocks are given in the following sections and the technicalities of the design are given. Furthermore, some examples of data gathered during test of the equipment concerning assessment of the reverberation and local bistatic scattering features are presented.

2

Passive acoustic detection and observations of wind-wave breaking processes

Dragan A., Klusek Z., Swerpel B.

Hydroacoustics

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2011

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Vol. 14

29-38

EN

This study is a preliminary work aiming to obtain statistics of wind waves on the base of the ambient sea noise parameters. In experiment conducted on the Baltic Sea, passive acoustic methods were exploited in order to detect and parameterize breaking evens. A four hydrophones array was used to record ambient sea noise for five days. Data collected during this experiment allowed us to track moving acoustic sources, to estimate their speed, duration and number in a unit of time. All these parameters were determined using generalized the cross correlation method. Some examples of obtained cross correlation time series with brief description of encountered difficulties in analysis are presented. Variation in number, duration and speed of breaking events in time are compared with averaged noise level and significant wave height. This last parameter, describing in a unified way the wave field, constitutes the essence of further investigations. Distributions of obtained values are shown and further improvement of a method is shortly introduced.

3

Preliminary investigations on implementation of technology of broadband signals for marine biology and sediments recognition

Klusek Z., Majewski P., Dragan A., Psuty I.

Hydroacoustics

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2010

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Vol. 13

143-152

EN

This paper describes potential applications of broadband acoustic signals for marine biology and fisheries and acoustic precise profiling of the upper layer of sediments. Comparisons of the results of conducted experiments employing the same experimental setup but with different signals are presented. In each of experiments short pulses of CW signals and long pulses of up/down chirp signals were used. The basic theory of FM signals as well as some of the factors that must be considered when implementing this type of signal in actual systems are described.

4

CW and CHIRP signals bottom backscattering in the PEZ of the Baltic sea

Klusek Z., Majewski P., Dragan A.

Hydroacoustics

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2010

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Vol. 13

135-142

EN

High-frequency bottom backscattering experiments were carried out in the Polish Economy Zone of the Southern Baltic Sea. CW and chirp signals were used to determine scattering reverberation as a function of the incident wave grazing angle and at vertical sounding. The chirp signals covered the frequency range from 40 to 80 kHz whilst the CW signals were selected at 40, 60 and 80 kHz. Acoustic data concerning the angular dependence of the backscattering were taken at the points where appropriate investigations of sediment properties had been earlier made by the Polish Geology Institute. The sediment types include not only acoustically hard fine and coarse sand bottom covered with gravel but also a flat muddy bottom. The results present the backscattering as a function of frequency, signal type and sediments properties. Times of reverberation and other statistical properties of returned signal are also discussed. When possible, due to more complete information on the sediments properties the measured backscattering strength was compared to the models developed by Jackson et al.

5

Modelling multistatic of target detection

Klusek Z., Elminowicz A., Tęgowski J., Szczucka J., Dragan A.

Hydroacoustics

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2008

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Vol. 11

131-138

EN

The paper presents a numerical approach to modelling the detection of underwater targets with a bi- or multistatic active sonar systems in the shallow water areas using different waveform signals. The results of the numerical modelling of surface, bubble clouds and bottom reverberation for CW and using up and down time-varying instantaneous frequency of chirp signals are presented. Some suggestions are made on the basis of the development and practicality for the shallow sea modeling techniques and approaches to existing sonar models. The paper reports the literature of the model components required for active sonar modelling for different propagation conditions. Some examples of scattering of CW and chirp source signals at bubble clouds and corrugated surfaces, and coherence are given. Active propagation and the system performance are surveyed and modelled adaptable to the specific environmental condition of the shallow sea area of the Gdansk Gulf.