caa a22 4500 397551649 CHVBK 20180308164752.0 cr unu---uuuuu 161202e199608 xx s 000 0 eng 10.1006/jmsc.1996.0087 doi (NATIONALLICENCE)oxford-10.1006/jmsc.1996.0087 Acoustic sampling and signal processing near the seabed: the deadzone revisited [Elektronische Daten] [E. Ona, R. B. Mitson] There are particular difficulties in making acoustic estimates of the abundance of demersal and semi-demersal fish. One possibility which exists in any survey situation is that the fish may move from the direct path of the vessel because of the noise it is radiating. However, the problems addressed here are primarily due to the physical characteristics of the transmitted acoustic pulse from the echo-sounder and its interaction with fish close to the seabed. This paper looks at the factors controlling the detection of these fish in terms of the acoustic sampling volumes near the bottom, the discrimination theoretically possible between fish and seabed echoes and the "depth anomaly”. The acoustic deadzone is defined and its volume is determined. Practical aspects of signal processing in this near seabed situation are then described, including seabed recognition and safeguarding fish signals from contamination by the bottom echo and from noise. Next, an echo-integrator deadzone comprising the acoustic deadzone, the backstep zone, and the partial integration zone (related to pulse length) is described and defined. Equations for calculating the effective volume or effective height of this deadzone are developed. Estimation errors due to the echo-integrator deadzone are investigated and equations derived for the necessary corrections. An example is shown of partial failure of the bottom recognition system and how the echo integrator result can be corrected to compensate. © 1996 International council for the Exploration of the Sea Articles nationallicence fish abundance estimation nationallicence near-seabed nationallicence acoustic deadzone nationallicence echo-integrator deadzone nationallicence Ona E. Institute of Marine Research P.O. Box 1870, N-5024, Bergen, Norway aut Mitson R. B. ACOUSTEC Swiss Cottage, 5 Gunton Avenue, Lowestoft, Suffolk, NR32 5DA, UK aut ICES Journal of Marine Science Oxford University Press 53/4(1996-08), 677-690 1054-3139 53:4<677 1996 53 icesjms https://doi.org/10.1006/jmsc.1996.0087 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1006/jmsc.1996.0087 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Ona E. Institute of Marine Research P.O. Box 1870, N-5024, Bergen, Norway aut NATIONALLICENCE 700 1- Mitson R. B. ACOUSTEC Swiss Cottage, 5 Gunton Avenue, Lowestoft, Suffolk, NR32 5DA, UK aut NATIONALLICENCE 773 0- ICES Journal of Marine Science Oxford University Press 53/4(1996-08), 677-690 1054-3139 53:4<677 1996 53 icesjms Metadata rights reserved CC BY-NC-4.0 http://creativecommons.org/licenses/by-nc/4.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-oxford