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1
Content available New signal processing in a passive sonar with gradient antenna
100%
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.
2
Content available Small antenna for a dipping sonar
100%
Marszal J. , Jedel A. , Ostrowski Z.
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tom Vol. 4
169--172
EN
The dome enclosing the antenna of dipping sonar should be of the smallest possible size. Presented in the paper is a concept of hydroacoustic antennas of active and passive sonar. The active antenna performs mechanical scanning while the passive antenna uses the orthogonal array of gradient hydrophones. In addition to that the antenna array includes ultrasonic transducers of a sound velocity profiler, a pressure sensor for measuring the depth of antenna submergence. With that many sources of signal in the sonar's ease, a multiple fibre cable is required or signal modulation to transmit the signals over a limited number of wires. The sonar in question uses distribution over time and an original modulation method for simultaneous transmission of several signals using a cable channel. Block diagram and formulas describing the entire signal from the sonar's antenna are included.
3
Content available Mutual Clutter Suppression Techniques for FM Sonars
88%
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.
4
Content available Bearing errors in passive sonar stationary target location
88%
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.
5
Redukcja wzajemnych zakłóceń w sonarach impulsowych z modulacja częstotliwości
88%
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.
6
Content available Time variable gain for long range sonar with chirp sounding signal
75%
Marszal J. , Ostrowski Z. , Schmidt J. , Kilian L. , Jedel A. , Schmidt A.
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tom Vol. 10
117-122
EN
The main purpose of applying Time Variable Gain (TVG) in active sonars with digital signal processing is to reduce dynamic range of echo signal and adapt it to the dynamic range of the analogue to digital conversion. With high transmission losses level, the dynamic range of the input signal in long range sonars can be very high and even exceed 200 dB. When chirp sounding signals with matched filtration are used, sonars can reach very long ranges. The article presents optimisation of TVG control for long range sonars. It also looks at the influence of chirp sounding signal compression, the result of digital matched filtration, for the TVG controlling. The examples of obtained results are presented.
7
Content available Multibeam sonar with hexagonal array
63%
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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