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Wyświetlanie 1-3 z 3
Tytuł:
On a threshold induced bias in fish target strength estimation
Autorzy:
Moszyński, M.
Powiązania:
https://bibliotekanauki.pl/articles/332238.pdf
Data publikacji:
2003
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
fisheries acoustics
marine organisms
Opis:
In fisheries acoustics the bias introduced by a system threshold in the integration of echoes from fish and other marine organisms has long been recognized. Some simple methods for evaluating such a bias uses Rayleigh assumption applied to fish backscattering length distribution. More adequate methods require that the target strength distribution of the fish and directivity pattern of the transducer be known. The method proposed here uses statistical approach for correction of target strength probability density function (PDF). The theory of conditional target strength PDF and conditional beam pattern PDF is derived. It provides correction not only for mean value of target strength but for whole distribution. The data obtained from simulations are presented and compared with those obtained from single-beam inverse processing.
Źródło:
Hydroacoustics; 2003, 6; 49-52
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effect of in situ radiated noise of the platform used on shallow water area on echo sounder data in fisheries-acoustics
Autorzy:
Brehmer, P.
Guennegan, Y.
Arzelies, P.
Guillard, J.
Cheret, Y.
Duformentelle, P.
Colon, M.
Powiązania:
https://bibliotekanauki.pl/articles/332717.pdf
Data publikacji:
2003
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
in situ
echo sounder
fisheries
acoustics
Opis:
The shallow water area of the coastal fringes is important to take into consideration in fish stock assessment because a great part of the stock, especially for the small pelagic fish is distributed in this area (20). In shallow water research vessels are prohibited to navigation (usually <20m) and usually only small boats can be used. One of the main source error in acoustics fish sampling is due to the avoidance reaction generated by the three dimensional noise diagram emitted by the boat. In this paper we highlighted the importance of wind direction and strength in the noise diagram emitted by the boat under in situ condition. A comparison of the noise level of two boats (a Research Vessel and a Speedboat equipped of similar echo sounder) has been made before simultaneous records of echo sounder data: the speedboat is more silent as revealed by in situ hydrophone measurement and near the ICES recommendations. The observation of shoal echo sounder descriptors shows an avoidance reaction as expected more important for the noisier boat: there the schools avoid more the research vessel. The avoidance reaction is characterised by a deeper position of the fish school barycentre, in the water column, detected by the research vessel and a shoal minimum depth higher than for the speedboat. The effect of noise diagram difference is clear on the same shoal descriptors, the difference appears for the vertical position of the barycentre and minimum altitude.
Źródło:
Hydroacoustics; 2003, 6; 31-40
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A simple standardisation of omnidirectional sonar in fisheries research through field calibration and sampling data
Autorzy:
Brehmer, P.
Gerlotto, F.
Powiązania:
https://bibliotekanauki.pl/articles/332471.pdf
Data publikacji:
2001
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
The paper presents a method making a comparison of acoustic results on schools through the use of omnidirectional sonar (possible). The weakness of such sonar for fisheries acoustics is that there is no practical way to accurately calibrate them, due to the fact that they are not designed specifically for scientific research. The procedure employed is through the use in the field of a reference target allowing to compare the echoes from one beam to the other and to evaluate roughly the operational threshold for school identification. Some results from a calibration achieved on a SIMRAD SR240 in Venezuela, 1998, are detailed.
Źródło:
Hydroacoustics; 2001, 4; 27-30
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-3 z 3

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