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Noise effect on parameters of quiet sonar with code modulation

Salamon Roman, Marszal Jacek, Jedel Andrzej

Vibrations in Physical Systems

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2023

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Vol. 34, nr 1

art. no. 2023109

EN

Earlier publications of the paper authors have shown that the use of code keying mixed with the CW FM sound signal allows the significant reduction in the distance measurement error, compared to classic silent CW FM sonar. In addition to the code modulation parameters, the magnitude of this error is influenced by the received input acoustic noise. The article shows the dependence of the input signal-to-noise ratio and the sound signal parameters on the target distance measurement error and the detection conditions, such as the output signal-to-noise ratio and the side lobe level. The results of the analysis were compared to the same parameters of the CW FM silent sonar without code modulation.

2

Method for the correlation coefficient estimation of the bottom echo signal in the shallow water application using interferometric echo sounder

Grall Piotr, Marszal Jacek

Vibrations in Physical Systems

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2021

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Vol. 32, nr 1

art. no. 2021103

EN

The article presents a new method for the assessment of bottom echo correlation coefficient in the presence of multiple echoes. Bottom correlation coefficient is a parameter that characterizes spatial properties of echo signal. Large variability of the bottom shape or properties (for example caused by the presence of bottom objects) and the presence of the acoustic shadow strongly influence the value of the correlation coefficient. There is a problem, however, in the proper determination of correlation coefficient of the bottom echo when more than one echo is present. In the shallow water application, the echoes coming to the hydroacoustic array from various directions influence the measured value of the correlation coefficient. The method proposed by the authors challenges this issue by applying a subarray processing based on the initial depth estimation. The article presents the preliminary research results and describes the limitations of the proposed method.

3

Numerical Model of Surface and Quasi-Spherical Sea Noise and Its Application to Analysis of DIFAR Systems

Rudnicki Mariusz, Salamon Roman, Marszal Jacek

Archives of Acoustics

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2021

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Vol. 46, No. 4

591--604

EN

Various types of passive sonar systems are used to detect submarines. These activities are complex and demanding. Therefore, computer simulations are most often used at the design stage of these systems. For this reason, it is also necessary to simulate the acoustic ambient noise of the sea. The article proposes a new numerical model of surface and quasi-spherical sea noise and presents its statistical parameters. The results of the application of the developed noise model to analyse the received signals of the DIFAR1 sonobuoy are also presented.

4

Underwater navigation system based on Doppler shift – measurements and error estimations

Ostrowski Zawisza, Salamon Roman, Kochańska Iwona, Marszal Jacek

Polish Maritime Research

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2020

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nr 1

180--187

EN

A new acoustic navigation system was developed to determine the position and speed of moving underwater objects such as divers and underwater vehicles. The path of an object and its speed were determined by the Doppler shifts of acoustic signals emitted by a transmitter placed on the object and received by four hydrophones installed at the periphery of the monitored body of water. The position and speed measurements were affected by errors mainly caused by acoustic reflections (returns) from the water body boundaries and surface reverberations. This paper discusses the source of the disturbances with the results of a simulation test and experimental measurements. It was demonstrated that the magnitude of the errors could be acceptable in most of the potential applications of the acoustic navigation system.

5

Shallow Water Experiment of OFDM Underwater Acoustic Communications

Kochańska Iwona, Schmidt Jan H., Marszal Jacek

Archives of Acoustics

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2020

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Vol. 45, No. 1

11--18

EN

The large variability of communication properties of underwater acoustic channels, and especially the strongly varying instantaneous conditions in shallow waters, is a challenge for the designers of underwater acoustic communication (UAC) systems. The use of phase modulated signals does not allow reliable data transmission through such a tough communication channel. However, orthogonal frequency-division multiplexing (OFDM), being a multi-carrier amplitude and phase modulation technique applied successfully in the latest standards of wireless communications, gives the chance of reliable communication with an acceptable error rate. This paper describes communication tests conducted with the use of a laboratory model of an OFDM data transmission system in a shallow water environment in Wdzydze Lake.

6

Impact of Spatial Noise Correlation on Bearing Accuracy in DIFAR Systems

Rudnicki Mariusz, Marszal Jacek, Salamon Roman

Archives of Acoustics

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2020

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Vol. 45, No. 4

709--720

EN

DIFAR type underwater passive systems are one of the more commonly used tools for detecting submarines. At the design stage, which usually uses computer simulations, it is necessary to generate acoustic noise of the sea. It has been shown that correlating noise significantly reduces these errors compared to the assumption that noise is uncorrelated. In addition, bearing errors have been shown to be the same in systems with a commonly used antenna containing five hydrophones, as in a system without a central hydrophone, which may be useful in some DIFAR system design solutions.