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    Wyświetlanie 1-8 z 8
    Tytuł:
    Correction of frequency distortion of the DDS signals
    Autorzy:
    Elminowicz, A.
    Zajączkowski, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/331959.pdf
    Data publikacji:
    2010
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    The Diver Detection Sonar (DDS) as a surveillance system has been designed to monitor the threat of underwater attacks against harbours, ships, naval bases, coastal industrial installations, oil platforms etc. This paper describes technical complexity of designing wideband DDS, with increased coverage effectiveness and following additional advantages: improved range resolution, high signal to noise and reverberation ratio and possibility operation of several sonars in the same frequency band using different type of modulation. The article presents technological principles and problems related to the wideband sig-nals transmitting and receiving by cylindrical piezocomposite transducer as well as implementation of the broadband compression technique for correction of frequency distortion.
    Źródło:
    Hydroacoustics; 2010, 13; 83-88
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Doppler effect in wideband sonars
    Autorzy:
    Elminowicz, A.
    Zajączkowski, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/332069.pdf
    Data publikacji:
    2004
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    To increase sonar range and to improve the range resolution and SNR, modern sonars use a matched filtration what corresponds to correlation between replica of transmitted sig-nal and received echoes. Motion of sound source or/and object causes frequency Doppler shift of received signals, thereby generating the distortion of the correlation processing of echo with signal replica. In the paper, the results of studies of sonar signals (CW, LFM and HFM) immunity to correlation distortions due to Doppler effect are presented. It has been demonstrated that only HFM signals are immune to adverse Doppler effect in correlation processing.
    Źródło:
    Hydroacoustics; 2004, 7; 31-36
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    High resolution multi-beam side looking sonar
    Autorzy:
    Elminowicz, A,
    Zajączkowski, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/332745.pdf
    Data publikacji:
    2005
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    The conventional side–scan sonars does not ensure sufficient angular and range resolution to detect very small objects with small target strength. Decrease of beam width leads to the increase of angular resolution but requires the decrease of towing speed what means reduction of searched area. Other method of the angular resolution increased is designing multi–beam sonar or sonar with synthetic aperture. The paper presents a design of effective multi–beam side looking sonars with a large angular and range resolution operates with 100 kHz, 200 kHz, 400 kHz and 600 kHz. The sonar, described in the paper, operates with 200 kHz frequency; LFM modulation – 20 kHz and 40 kHz band; array provides 32 elements with d/ë spacing what ensure a shaping of 5 or 9 beams with 0,40° width. The range of sonar is from 250 m to 300 m, the level of side lobes are smaller than -20 dB and level of grating lobes for 5 beams are smaller than -30 dB. The principle of sonar performance and wideband effective processing are presented. Effectiveness of processing depends on beams number and decrease of beams number, together with the range increased, leads to increase of processing effectiveness.
    Źródło:
    Hydroacoustics; 2005, 8; 37-46
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Application of DDS and magnetic barrier cooperating with acoustic barriers and tethered sonobuoys for harbour and anchorage underwater protection
    Autorzy:
    Elminowicz, A.
    Zajączkowski, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/331708.pdf
    Data publikacji:
    2011
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    The underwater protection system that consists of wideband Acoustic Barriers (WAB) and wideband DDS (WDDS) is a very suitable acoustic device to operate in Littoral Water (LW) and Extremely Littoral Water (ELW). A new approach to underwater protection harbour and task group on the anchorage against AUV, DDV and torpedos is focused on designed stationary tethered sonobuoys with passive sonar, active multistatic sonar, intercept sonar and also possibility of jamming intercepted underwater objects. Passive omnidirectional sonar may be used for initial detection of intruder on the long distance (up to 5 km) and active multistatic sonar will be applied for detection and precise location of detected object. Intercept sonar is waiting for homing sonar signals generated by AUV, DDS, torpedos or submarines and received signals are basis generating jamming signals. The paper describes the WAB, WDDS and magnetic barrier integrated to short range (up to 1000 m) protection systems. The long range (up to 5000 m) sonobuoy – for various technical parameters and environmental conditions – has been studied.
    Źródło:
    Hydroacoustics; 2011, 14; 39-46
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Multistatic systems
    Autorzy:
    Elminowicz, A.
    Zajączkowski, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/332386.pdf
    Data publikacji:
    2006
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    This paper describes key features of a multistatic operation in the littoral beginning from multistatic system (MS) configuration, his performance model and constraints imposed by environment of shallow water. The architecture of MS, features and requirements of MS basic subsystem has been presented. Essential role as during MS operation is fulfilled by data fusion and tracking methods as well a communication between MS units, has been protruded. The application of MS, especially for underwater protection systems, in the form of barriers protecting anchorage, harbour, straits or entries to the harbour has been presented. Other applications are connected with military operation, especially Anti–Submarine Warfare (ASW) in littoral areas. Attention was paid on possibility of cooperation among the different acoustics devices in MS.
    Źródło:
    Hydroacoustics; 2006, 9; 57-64
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Mutual interferences reduction between sonars or barrier modules operating in the same area
    Autorzy:
    Elminowicz, A.
    Zajączkowski, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/332459.pdf
    Data publikacji:
    2007
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    This paper describes key features of a Mutual Interference Reduction (MIR) in sea area, especially in shallow water, where some acoustic devices may operate simultaneously. MIR is an essential problem in mono– and multistatic systems. Receivers of sonars or barrier modules, operating in these systems, can receive signals from other acoustic devices by direct track, as echoes from the targets or as reverberations. The mutual sonars interference level depends on many parameters, like: the transmitting signal parameters (modulation, SL, B, T) and bands aliasing, mutual sectors coverage, the distance and mutual localization of trans-mitting transducers and receiving arrays, as well as type of matched filtration. The degrada-tion of mutual interferences by matched filtration has been determined. Influence of modula-tion type, B and T parameters on MIR at the matched filtration output have been presented also.
    Źródło:
    Hydroacoustics; 2007, 10; 39-44
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Multifrequency wideband sonar array
    Autorzy:
    Elminowicz, A.
    Lis, W.
    Zajączkowski, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/332415.pdf
    Data publikacji:
    2012
    Wydawca:
    Polskie Towarzystwo Akustyczne
    Opis:
    This paper describes of new approach to Multifrequency Wideband Arrays (MWA), applied piezocomposite technologies of the array elements. MWA operating in transmitting (Tx) and receiving (Rx) mode on two or three bands, requires state-of-the-art technology and efficient array designing than conventional array in which separate arrays for every band or even separate Tx and Rx transducers/arrays are used. The new piezocomposite elements are designed at OBR Centrum Techniki Morskiej S.A., manufactured by Materials Systems Inc. (Littleton, USA) and tested at the cooperation with Gdansk University of Technology. The article presents research and development work at the multifrequency wideband piezocomposite arrays elements. An example of dual frequency wideband Tx/Rx array with design parameters and its implementation for the dual frequency wideband sonar will be presented. The results of array elements measurements: TVR, RVS, Impedance and Phase versus frequency from 50 kHz to 500 kHz as well as beam patterns, will be also presented.
    Źródło:
    Hydroacoustics; 2012, 15; 33-38
    1642-1817
    Pojawia się w:
    Hydroacoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Can seabirds modify carbon burial in fjords?
    Autorzy:
    Weslawski, J.M.
    Urbanski, J.
    Gluchowska, M.
    Grzelak, K.
    Kotwicki, L.
    Kwasniewski, S.
    Legezynska, J.
    Wiktor, J.
    Wlodarska-Kowalczuk, M.
    Zaborska, A.
    Zajaczkowski, M.
    Stempniewicz, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/47719.pdf
    Data publikacji:
    2017
    Wydawca:
    Polska Akademia Nauk. Instytut Oceanologii PAN
    Tematy:
    sea bird
    sediment
    organic matter
    Kongsfjorden
    microplankton
    carbon source
    Svalbard Fjord
    Opis:
    Two high latitude fjords of Spitsbergen (Hornsund 77°N and Kongsfjorden 79°N) are regarded as being highly productive (70 g and 50 gC m−2 year−1) and having organic-rich sediments. Hornsund has more organic matter in its sediments (8%), nearly half of it of terrestrial origin, while most of that in Kongsfjorden (5%) comes from fresh, marine sources (microplankton). Analysis of the carbon sources in both fjords shows that a major difference is the much larger seabird population in Hornsund-dominated with over 100 thousands pairs of plankton feeding little auks in Hornsund versus 2 thousand pairs in Kongsfjorden, and marine food consumption estimated as 5573 tonnes of carbon in Hornsund, versus 3047 tonnes in Kongsfjorden during one month of chick feeding period. Seabird colonies supply rich ornithogenic tundra (595 tonnes of C, as against only 266 tonnes of C in the Kongsfjorden tundra). No much of the terrestrial carbon, flushed out or wind-blown to the fjord, is consumed on the seabed – a state of affairs that is reflected by the low metabolic activity of bacteria and benthos and the lower benthic biomass in Hornsund than in Kongsfjorden.
    Źródło:
    Oceanologia; 2017, 59, 4
    0078-3234
    Pojawia się w:
    Oceanologia
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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