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1
Content available Determining the distribution of acoustic field intensity using the sound ray density method
100%
Gawrysiak J. , Salamon R.
Hydroacoustics
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2000
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tom Vol. 3
99--104
EN
The article presents a numerical method for determining the intensity of sound. The method is based on surface density of sound rays. It assumes that a ray of sound carries a specific acoustic power. As a result, it is no longer necessary to determine intensity in caustics, especially given the fact that intensity determined in caustics using the method employed so far has an infinite value.
2
Content available Code signals transmission using MFSK modulation in shallow waters
80%
Zachariasz K. , Schmidt J. , Salamon R.
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tom Vol. 4
261--264
EN
The paper presents an acoustic system for the transmission of digital data in shallow coastal waters of which multi-path propagation and intense reverberations are characteristic. To ensure a small error probability of moderate speed transmission, the system uses corrective codes and a technique of incoherent modulation MFSK (Mufti Frequency Shift Keying). To synthesise the transmission signal, estimate the spectrum of the signal received and code and decode the channels, a DSP processor was used. The paper includes the results of a computer simulation in which the system was put to work in the presence of Gaussian noise. The system was tested in shallow coastal waters and the results are discussed in the paper.
3
Content available Visual representation of the effects of spatial and frequency filters applied in passive sonars
80%
Raganowicz A. , Salamon R. , Rudnicki M. , Kilian L.
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tom Vol. 4
213--116
EN
The operator of a passive sonar should be able to discern the direction (bearing) of a submerged, noise-producing object. Interference to bearing comes from reverberations, noise from the sea, man-made noise and noise generated by other objects. The article presents methods of spatial and frequency filtration designed to provide various forms of display of those fragments of the spectrum that are of interest to the operator. The operator makes his selection on the basis of many spectrograms that are produced during the successive listening cycles, displayed on the monitor. The amplitudes of spectral lines in the spectrograms are presented as lines of various lengths and colours. The summation spectrum of the displayed listening cycles is presented, too. The lines from a selected spectral range are shown on the panoramic amplitude graph in the function of the bearing angle. Thanks to that the determination of the location of the source of sound is significantly improved. The source of sound can also be discerned by using a reverse technique whereby a group of spectral lines is determined on the basis of a selected sector of angular observation.
4
Content available Principles of computing and displaying the results of detection by underwater systems as part of sound velocity measurements
80%
Raganowicz A. , Kilian L. , Salamon R.
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tom 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.
5
Hydroakustyczny system transmisji danych w wodach płytkich z zastosowaniem modulacji MFSK
80%
Schmidt J. , Zachariasz K. , Salamon R. , Kilian L.
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tom Vol. 83, nr 27
289-292
EN
The paper presents a hydroacoustic system for the transmission of digital data in shallow coastal waters of which multi-path propagation and intense reverberations are characteristic. To ensure a small error probability of moderate speed transmission, the system uses Corrective Hamming's codes and a technique of incoherent modulation MFSK (Multi Frequency Shift Keying). To synthesise the transmission signal, estimate the spectrum of the signal received and code and decode the channels, a DSP processors are used. The paper includes the results of a simulation in which the system was put to work in the presence of Gaussian noise. The system was tested in shallow lake waters and the first results are discussed in the paper.
6
Content available New signal processing in a passive sonar with gradient antenna
80%
Salamon R. , Marszal J. , Kilian L. , Jedel A.
Hydroacoustics
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2000
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tom Vol. 3
129--134
EN
The well-known set up of an acoustic source bearing consists of four ultrasonic transducers located in the corners of a square and an additional fifth transducer placed in the centre of the square. The subtractions of the signals from the opposite transducers are proportional to sine and cosine of the angle of the arrival wave. The subtracted signals are modulated by the signal from the central transducer and treated as co-ordinates (X, Y) of the points exposed on the display with the Cartesian co-ordinate system. However such a simple solution has one serious limitation, viz., it gives satisfactory results only when a signal to noise ratio is high enough, because the noise frequency band is large compare with the bandwidth of measured signal. The paper presents an improved version of the system. Received signals are sampled and their discrete Fourier transforms are calculated. Every spectral line in DFT is presented as an individual point on the monitor. The angular position of the point shows the direction of the wave arrival and the distance from the co-ordinate origin is proportional to the power of the spectral line.
7
Content available Mutual Clutter Suppression Techniques for FM Sonars
71%
Marszal J. , Rudnicki M. , Jedel A. , Salamon R. , Kochańska I.
Archives of Acoustics
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2016
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tom 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.
8
Content available Signal processing in the hydroacoustic ships berthing aid system
71%
Marszal J. , Salamon R. , Kilian L. , Raganowicz A. , Szurowski T.
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tom Vol. 1
237--242
EN
The berthing of ships is an extremely complicated task that requires decisions on the movement of ships based on a large number of variabies: tide wind, visibility, speed, distance from jetty. Particular difficulties are related to the less maneuverable ships such as very large crude carriers. The presented hydroacoustic ships berthing aid system measures four distances of a ship to the jetty using the sonar echo method. The system computer calculates the bow and stern speed and distances to dolphins from the measured data. The results obtained are simultaneously presented on a large, high luminance display as well as printed out and recorded on computer discs. Additionally the dolphins displacements are measured and the data obtained together with its statistical parameters are recorded.
9
Content available Bearing errors in passive sonar stationary target location
71%
Schmidt A. , Marszal J. , Salamon R. , Jedel A. , Ostrowski Z.
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tom 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.
10
Content available Method for improving multibeam sonar bearing accuracy
71%
Leśniak W. , Marszal J. , Salamon R. , Zachariasz K. , Schmidt J.
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tom 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.
11
Wpływ gradientów prędkości na charakterystykę kierunkowa przetworników ultradźwiękowych
71%
Gawrysiak J. , Salamon R. , Kaczmarek J. , Raganowicz A. , Rudnicki M.
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tom Vol. 83, nr 27
263-268
EN
The usual assumption made in sound ray tracing is that the beam pattern will be conic. Approximation of the actual beam pattern using a conic beam is a way to simplify the maths. At the same time, it reinforces what is a false view, namely that side lobes have no effect on the detection capabilities of hydroacoustic systems. The article presents a short description of the sound ray density method which apart from eliminating the problem of computing field intensity in caustics area also enables the inclusion of actual beam patterns of ultrasound transducers. Further in the article, several examples are given of field intensity distribution generated by real transducers. The effect of non-homogeneous media on the distortion of the beam pattern is discussed, too.
12
Redukcja wzajemnych zakłóceń w sonarach impulsowych z modulacja częstotliwości
71%
Jedel A. , Salamon R. , Marszal J. , Kaczmarek J. , Ostrowski Z.
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tom Vol. 83, nr 27
281-284
EN
Some of important disturbances in sonar echo are signals emitted by the other sonars. Sonar receives these signals by the direct trace or as echoes from the targets. The mutual interference level depends on many parameters, like: the sounding frequency bands aliasing, the distance between sonars and the mutual localization of sonar transducers. The mutual interference of sonars is particularly sharp when the same type of sonars (with the same frequency bands) is used in the same area The analysis of such situations is presented in the paper. Some solutions of mutual interference reduction for pulse sonars with linear frequency modulation and match filtering with FFT technique, designed in Technical University of Gdansk, are given. The results of computer simulations are presented. It is possible to obtain the 40 dB reduction of mutual interference.
13
Content available Multibeam sonar with hexagonal array
51%
Salamon R. , Marszal J. , Kilian L. , Jedel A. , Ostrowski Z. , Raganowicz A. , Rudnicki M. , Wofan Z. , Zachariasz K.
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tom Vol. 2
133--138
EN
The paper presents a multi-beam digital sonar that was designed for monitoring and fish stock assessment in in/and waters. The sonar can also be used as a bottom profiler in lakes, rivers and shallow sea areas. The hexagonal piezoelectric transducer array co-operates with a commutator set. The 32 -channel digital beamformer creates 30 narrow receiving beams in every 60o sector of simultaneous observation. The six sectors cover the whole 360o angle range of the sonar. The beamformer digital signal processing is based on second order sampling of echo signals and the phase-shifting principle of beam deflection. The sonar block diagram, beamformer algorithms, as well as transducers designs are discussed.
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