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1
Content available Analysis of distance measurement errors in CW FM sonar with MLS code modulation
Jedel A., Marszal J., Salamon R.
Hydroacoustics
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2017
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Vol. 20
75--84
EN
Although used in the classic silent sonar, the CW FM sounding signal has a major flaw which is its inaccuracy in determining the distance to a target. The authors of the article have developed a concept of silent sonar using frequency modulation signals switched by pseudorandom codes, already discussed in their previous work. This article presents a detailed analysis of errors in CW FM sonar with pseudo-random sequence code modulation confronted with errors which occur in similar sonar without code modulation.
2
Content available Continuous wave sonar with hyperbolic frequency modulation keyed by pseudo-random sequence
Jedel A., Marszal J., Salamon R.
Hydroacoustics
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2016
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Vol. 19
185--196
EN
A CW FM type sounding signal is used in the classical solution of silent sonar. While the signal provides a relatively simple implementation of digital signal processing, and ensures good detection conditions, unfortunately, in the presence of the Doppler effect, distance measurement results tend to be wrong. This is due to the fact that the received signal’s instantaneous frequency value is dependent both on the distance to the object, and its speed. Sounding signal, as patented by the authors, is a combination of Pseudo-Random Sequences (PRS), and elementary signals of Hyperbolic Frequency Modulation (HFM) type. The structure of this signal is aimed at minimizing measurement error. The article presents the idea of a sounding signal of HFM+PRS type, and the results of computer simulations.
3
Content available Mutual Clutter Suppression Techniques for FM Sonars
Marszal J., Rudnicki M., Jedel A., Salamon R., Kochańska I.
Archives of Acoustics
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2016
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Vol. 41, No. 4
721--729
EN
The article presents methods that help in the elimination of mutual clutter as well as the consequences of two FM sounding signal sonars operating in the same body of water and frequency band. An in-depth analysis of mutual clutter was carried out. The effects of sounding signal differentiation were determined, as was the Doppler effect on mutual clutter suppression. One of the methods analysed is of particular interest in a situation in which collaborating sonars are operating in opposite frequency modulation directions. This method is effective for both linear and hyperbolic frequency modulations. A formula was derived, identifying exactly how much quantities of clutter may be lessened. The work included comprehensive computer simulations and measurements as well as tests in real-life conditions.
4
Content available Detection Range of Intercept Sonar for CWFM Signals
Marszal J., Salamon R.
Archives of Acoustics
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2014
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Vol. 39, No. 2
215--230
EN
Stealth in military sonars applications may be ensured through the use of low power signals making them difficult to intercept by the enemy. In recent years, silent sonar design has been investigated by the Department of Marine Electronic Systems of the Gdansk University of Technology. This article provides an analysis of how an intercept sonar operated by the enemy can detect silent sonar signals. To that end a theoretical intercept sonar model was developed with formulas that can numerically determine the intercept ranges of silent sonar sounding signals. This was tested for a variety of applications and water salinities. Because they are also presented in charts, the results can be used to compare the intercept ranges of silent sonar and traditional pulse sonar.
5
Content available Distance measurement errors in silent FM-CW sonar with matched filtering
Marszal J., Salamon R.
Metrology and Measurement Systems
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2012
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Vol. 19, nr 2
321-332
EN
The secretiveness of sonar operation can be achieved by using continuous frequency-modulated sounding signals with reduced power and significantly prolonged repeat time. The application of matched filtration in the sonar receiver provides optimal conditions for detection against the background of white noise and reverberation, and a very good resolution of distance measurements of motionless targets. The article shows that target movement causes large range measurement errors when linear and hyperbolic frequency modulations are used. The formulas for the calculation of these errors are given. It is shown that for signals with linear frequency modulation the range resolution and detection conditions deteriorate. The use of hyperbolic frequency modulation largely eliminates these adverse effects.
6
Content available Application of maximum length sequence in silent sonar
Marszal J., Salamon R., Kilian L.
Hydroacoustics
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2012
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Vol. 15
143-152
EN
Silent sonars are designed to reduce the distance over which their sounding pulses can be detected by intercept sonars. In order to meet this objective, we can use periodical sounding signals that have low power, a very long duration and wide spectrum. If used in the silent sonar’s receiver, matched filtration ensures very good detection of motionless or slow moving targets. However, it is more difficult to detect echo signals of fast moving targets with Doppler effect causing significant error in target distance measurements. In an effort to find signals that can better resist Doppler effect, maximum length sequence was tested for its application in silent sonar. It has an elementary signal which includes linear frequency modulation. It was demonstrated that the signal produces much better results than those obtained with simple frequency modulation signals.
7
Content available Silent sonar with matched filtration
Salamon R., Marszal J., Schmidt J., Rudnicki M.
Hydroacoustics
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2011
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Vol. 14
199-208
EN
Radars with continuous wave frequency (CW FM sonars) are used in radiolocation as ‘silent radars’. They determine the distance to target by measuring the difference between the frequency of the sounding signal and echo signal. The article presents the principle of operation and parameters of silent CW FM sonars. Target distance determined by these sonars is based on the signal at the output of the matched filter. The Doppler effect is studied in detail to identify its effect on the sonar’s parameters. The results of theoretical calculations are presented together with the results of the sonar’s computer simulation.
8
Content available Doppler effect in the cw fm sonar
Marszal J., Salamon R., Zachariasz K., Schmidt A.
Hydroacoustics
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2011
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Vol. 14
157-164
EN
When sonars are used for military purposes they have to ensure unobtrusive operation, afeature that can be potentially secured by ‘silent sonars’ or continuous wave frequency modulation sonars (CW FM sonars). The article presents how these sonars operate and identifies the relations between their parameters. The Doppler effect and its impact on the CW FM sonar are studied to identify how it affects the sonar’s parameters. The results of simplified theoretical calculations are supported with results of computer simulations of a more realistic model.
9
Content available Modernization of ASW sonar SQS-56 at Gdansk University of Technology
Marszal J., Schmidt J., Salamon R., Kilian L., Raganowicz A., Zachariasz K., Ostrowski Z., Jedel A., Rudnicki M., Sidorko T.
Hydroacoustics
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2010
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Vol. 13
191-196
EN
The fast development of electronic technology and digital signal processing methods makes electronic devices, including sonar systems ones, obsolete very quickly. On the other hand the ships mechanical components including mechanical parts of sonars are operational for a few dozens of years. It makes good opportunity to modernize these devices by using modern electronic devices and new digital signal processing methods with application of existing antenna and mechanical systems. The paper presents the modernization of ASW sonar SQS-56 on the Polish frigate ORP “Kościusko”. The aim of modernization, the new parameters of the sonar and block diagram after modernization are presented.
10
Content available Doppler estimation method for moving target location
Salamon R., Marszal J.
Hydroacoustics
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2010
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Vol. 13
225-234
EN
The article presents an algorithm for target location based solely on Doppler shift of echo acoustic signals of a moving underwater object. The algorithm is designed for use in multi-static systems for protecting bodies of water from terrorist attacks by divers or submerged vehicles. The original source of signals is a transmitter emitting continuous acoustic waves. The echo signals from moving object are received by hydrophones located at fixed and known points in the water. Doppler shifts are determined from discrete Fourier transforms of hydrophone signals. The proposed iterative algorithm for target location calculates the approximate values of target speed vector and target coordinates which correspond to speed vectors as calculated previously.
11
Content available Method for improving multibeam sonar bearing accuracy
Leśniak W., Marszal J., Salamon R., Zachariasz K., Schmidt J.
Hydroacoustics
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2009
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Vol. 12
98-108
EN
The paper presents a simple method for improving multibeam sonar bearing accuracy. The principle proposed here is similar to the monopulse method, a solution commonly used in radars and sonars. With no manual or automatic beam rotation, the method offers a substantial reduction in the demand for sonar computational effort. It significantly reduces bearing error for a relatively high signal to noise ratio. The paper gives a boundary value of the output signal to noise ratio which when exceeded satisfactorily improves bearing accuracy.
12
Content available Bearing errors in passive sonar stationary target location
Schmidt A., Marszal J., Salamon R., Jedel A., Ostrowski Z.
Hydroacoustics
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2009
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Vol. 12
189-200
EN
The paper presents a method for determining the coordinates of stationary targets using passive sonar bearing. It identifies the requirements sonar movements must meet to keep the incorrect determination of coordinates to a minimum. It gives the relations, which help determine coordinate errors analytically. Numerical experiments are used to demonstrate the success of the analysis.
13
Zmodyfikowana metoda monopulsowa w wielowiązkowych filtrach przestrzennych sonarów pasywnych
Leśniak W., Salamon R.
Zeszyty Naukowe Wydziału ETI Politechniki Gdańskiej. Technologie Informacyjne
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2006
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T. 9
151-158
PL
Zwiększenie dokładności określenia namiaru celu można uzyskać w sonarach stosując metodę monopulsową. W konwencjonalnych sonarach polega ona na wyrównywaniu sygnałów w dwóch sąsiednich wiązkach poprzez obrót anteny. W cyfrowych sonarach wielowiązkowych obrót anteny można zastąpić obliczeniami, które przedstawiono w referacie. Opracowaną metodę poprawy dokładności namiaru pokazano na przykładzie szerokopasmowego sonaru wielowiązkowego z anteną liniową. Wyznaczono błędy namiaru spowodowane szumami morza. Zaproponowano sposób zmniejszenia błędu systematycznego pojawiającego się przy małych stosunkach sygnału do szumu.
EN
In order to increase bearing accuracy in passive sonars the monopulse techniques can be used. In conventional systems the monopulse concept is realized by equalizing the signal amplitudes in two adjacent beams by appropriate rotation of the sonar array. In digital multibeam sonars the array rotation can be replaced by special numerical procedure presented in the paper. The proposed method was implemented for the linear array. The bearing errors originated from ambient sea noise were estimated. In addition, the bias reduction procedure was proposed for the case of law signal-to-noise ratio.
14
Content available Electronic stabilization of beams in sonar with cylindrical array
Marszal J., Leśniak W., Salamon R., Schmidt J.
Hydroacoustics
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2006
|
Vol. 9
119-124
EN
The article presents the principle of operation of the beamformer of sonar with a cylin-drical array. It demonstrates that a modified beamformer can be used for beam electronic stabilization. The paper presents the algorithm of a digital beamformer used to ensure that the beam’s axis is maintained in a horizontal plane when the ship’s pitch and roll are known. Finally, the article gives an overview of the technical problems of electronic beam deflection.
15
Content available Underwater communication system for shallow water using modified MFSK modulation
Schmidt J., Zachariasz K., Salamon R.
Hydroacoustics
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2005
|
Vol. 8
179-184
EN
The paper describes the design and operation of the Modified MFSK system for underwater communication. Its function is to transmit data and commands from ships to underwater objects in shallow coastal waters and lakes. The system was primarily required to ensure energy efficiency in its underwater section and the minimum of transmission errors. The emphasis was on non-linear distortions produced in piezoelectric transducers, an untypical source of errors.
16
Content available Processing the complex signal in the acoustic processor of a sonobuoy system
Raganowicz A., Rudnicki M., Salamon R.
Hydroacoustics
|
2005
|
Vol. 8
163-170
EN
The article presents digital methods for processing the complex signal in the acoustic processor of a sonobuoy. The overall system design and the complex signal are presented. Two alternative methods for signal processing are discussed: in the time domain and in the frequency domain. Block diagrams of the algorithms of both processing methods are included. The problems involved in the practical implementation of data analysis methods are discussed. The problems are produced by the phenomena occurring in the system’s analogue section and by the complexity of the computation related to how powerful the digital algorithms are. The computation errors in both methods are analysed. The advantages and disadvantages of the different signal processing methods are discussed, with emphasis on the practicality of the device. The advantage of the processing method in the frequency domain is explained. Graphic images of the results of both processing methods are included on the example of real signals received during the study.
17
Content available OFDM modulation and adaptive equalization for underwater communications
Kochańska I., Lasota H., Salamon R.
Hydroacoustics
|
2005
|
Vol. 8
77-82
EN
Transmission performances of a shallow underwater channel are limited due to multiple reflections of sound waves off the bottom and water surface, and to the non-stationarity caused mainly by water surface movement. In traditional narrowband telecommunication modems complex Decision Feedback Equalizers are used for minimizing the influence of intersymbol interferences caused by multipath propagation of sound waves. The article proposes adapting OFDM modulation and adaptive equalization based on Kalman filtration techniques for use in underwater communications system. The OFDM modulation is used in wideband ADSL telecommunication modems. The Kalman filtration algorithm is used for time-varying processes identification. The techniques were tested in simulation environment with promising results.
18
Content available Dynamic control of the receiving beam horizontal cross-section in the side scan sonar
Jedel A., Kilian L., Marszal J., Ostrowski Z., Salamon R.
Hydroacoustics
|
2005
|
Vol. 8
69-76
EN
A decade old side scan sonars are now being modernised by way of dynamically controlling the width of the receiving beam in the horizontal cross-section. The result is a quasi-constant linear resolution of the sonar (replacing constant angular resolution), when it picks up echo signals as it moves further away from the targets. The advantage of the treatment is that the ship using the side scan sonar can increase its speed without risking the loss of near targets’ echo. The articles describes how the system of dynamic control was implemented. Special TVG systems were introduced to control dynamic signal gain from several separate sections of the sonar’s acoustic array, which was divided symmetrically into unequal sections. The location of these systems in the sonar’s receiver is presented. Examples are given of curves that control TVG and of the effects of dynamic horizontal stabilisation of the sonar’s linear resolution as it receives signals.
19
Content available A directional sonobuoy system for submarine detection
Salamon R.
Hydroacoustics
|
2004
|
Vol. 7
195-208
EN
This article outlines the methods of detecting and locating submarines. Special attention is paid to the airborne system utilizing directional sonobuoys. The article discusses operating principles of such systems, a method of detecting and estimating the approach direction of the acoustic wave emitted by the vessel, and practical visualization methods. The article is related to the successful development of a Polish prototype of a directional sonobuoy acoustic system processor.
20
Content available Principles of computing and displaying the results of detection by underwater systems as part of sound velocity measurements
Raganowicz A., Kilian L., Salamon R.
Hydroacoustics
|
2003
|
Vol. 6
267--274
EN
The paper presents the upgraded system for measurements of sound velocity profiles and for computing and imaging the terms of detection in different hydrolocation and hydrocommunication systems. Three types of computations made by the system's processors are discussed. The most interesting task is to link the propagation routes and ray density with the parameters of the hydroacoustic system to obtain the desired display of the conditions to detect the signal from the background noises. Presented discussion of methodology of determining detection conditions using different forms of range equation gives a more detailed description of this task. In the next part of this paper the software's display function and necessary settings are specified and discussed. In the end two examples of computed detection conditions images (for active and passive sonar) are shown.
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