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1
Content available Simulation algorithms for DOA estimation with UCA
Janowski T., Porosińska E.
Hydroacoustics
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2012
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Vol. 15
65-74
EN
Multi-sensors passive arrays are used to detect different objects emitting wideband acoustic signal to aquatic medium. The most important design problem is to proper match the size of the antenna and number of sensors to the wideband frequency range. Especially the multimode operation significantly increases the detection efficiency. In case of cylindrical antennas interesting is object detection at two frequencies. The first frequency results directly from the antenna radius, whereas the second one is doubled. The article presents detection capabilities of antennas composed of several hydrophones.
2
Content available Location of the hydroacoustic noise sources performed by distributed passive sonar
Janowski T., Porosińska E.
Hydroacoustics
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2012
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Vol. 15
75-82
EN
Hydroacoustic location of underwater sound sources is commonly used to protect naval bases or military sea areas from various threats. Sonar technology applies hydrophones to detect sources of underwater noises. DOA estimation method based on the high angular resolution MUSIC algorithms are commonly used for small size antennas composed of hydrophones. The article proposes another approach to this problem. Additional equipage of the hydrophone with the GPS receiver and radio transreceiver enables construction of the distributed antenna. The size of such antenna can be significantly higher in comparison to the classical passive antenna. The article describes the algorithms of the sound sources location, results of the computer simulation and possibilities of hydrophone manufacturing as well its practical usage.
3
Content available Target tracking using multiple passive sonars
Janowski T., Porosińska E.
Hydroacoustics
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2011
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Vol. 14
69-74
EN
The DOA estimation methods based on the analysis of the noise subspace enable high resolution bearing determination of naval objects emitting hydrouacoustic noise. The knowledge of the objects number is the essential parameter for DOA algorithms. Practically, the number of the objects is unknown. In case of high sea ambient noise to object signal ratio the detection with desired probability is significantly hindered. In the event of system based on the console the detection decision belongs to the operator. The visual analysis of the reception beamformer changes conducts to the intruder detection. Whereas in case of the standalone systems the decision making process is performed by the detection and tracking algorithm. This article describes such algorithm based on the analysis of the machine states.
4
Content available Modified music algorithm for DOA estimation using the a-priori defined unitary matrix
Janowski T., Porosińska E., Zając R.
Hydroacoustics
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2009
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Vol. 12
77-82
EN
The determination of the number of the simultaneously observed objects is an important problem of the MUSIC algorithm. As the result of the covariance matrix eigendecomposition the eingevector and unitary matrix are obtained. The unitary matrix defines the transformation of the measurement vector. Consequently the obtained vector is orthogonal to the noise subspace. The solution of the eigendecomposition problem can be avoided assuming a-priori knowledge of the unitary matrix. Practically, the passive sonar detects the first appeared noisy object. This enable to beforehand define the set of the unitary matrixes exactly matched to the previously determined directions of the signal arrival. The article presents the form of the matrix and features of the measurement vector transformation. The results of the DOA algorithm computer simulation for passive sonar composed of four hydrophones developed in the OBR CTM S.A. are also presented.
5
Content available Theoretical problems of the wideband sonar time-spatial filtration
Janowski T., Kotłowski A., Porosińska E.
Hydroacoustics
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2003
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Vol. 6
221--228
EN
The paper presents the synthesis of the time-spatial matched filtration algorithm. First part specifies base for the algorithm-input data. Successively, the matched filtration for continuous junction is depicted. This leads to the canonical form of the time-spatial filter. Consecutively, the decomposition into series connection of the matched and spatial filtration is realized. The next step is the signals approximation by Fourier series due to equivalence between approximation and interpolation on uniformly distributed discrete sampIes. The equation of the spatial filtration - in frequency domain - results from this mathematical operations. Application of the Bluestein's method to solve this equation provides to the final algorithm version. Advantages of the developed algorithm are presented in conclusions.
6
Content available Stationary sonar for shallow water
Elminowicz A., Porosińska E., Kotłowski A.
Hydroacoustics
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2001
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Vol. 4
61--64
EN
The aim of the paper is checking possibility of building active stationary sonar designed for work in very shallow water, depth 8 - 10 m. Sonar is designed for monitoring very weak and moving targets by TS about -20 dB at the range up to few hundred metres. This paper presents construction of wide-sector sonar consists of two linear transducers. Beampatterns of the transducers are adjusted to conditions existing in very shallow water, particularly to minimize bottom and surface reverberation and effect of multipath propagation. Below are presented results of tests and measurements made for different types of targets and different environmental conditions - including: state of the sea, strong aeration of the near surface water, and influence of different sound propagation conditions for detection of the targets. The paper contains results of influence few types of signal processing for improvement SNR, thus increasing probability of the targets detection.
7
Content available Badanie przetwornika o nierównomiernie rozmieszczonych elementach
Elminowicz A., Porosińska E.
Hydroacoustics
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2000
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Vol. 3
135--140
EN
General object of nonuniform array design is the approximation of desired beam pattern with reduced number of elements which are required for uniform array of d/α=0,5. This work intends to study possibilities of design procedures lead to useful, nonuniform arrays with elements situated in raster d/α=0,5. Options of spacing elements for nonuniform arrays presented beneath are reduced to the raster d/α=0,5, which enable easier technical realisation of the beamformer. Arrays with equal excited elements have been used, what is highly practical, both for transmission and receiving. Many designs of arrays have been proposed and tested The beam patterns for steered beams are presented.
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