Target strength analysis in high fish densities using a probing split beam transducer

Abstract only. Journal home page: http://scitation.aip.org/jasa

High-resolution target strength measurements in deep water

Abstract only. Journal home page: http://scitation.aip.org/jasa

A summary of target strength observations on fisheries from the shelf off West Africa

Abstract only. Journal home page: http://scitation.aip.org/jasa

Simple calibration technique for the split-beam echo-sounder

The split-beam echo-sounder is used to measure the target strength of fish. Calibration of this instrument requires sensitivity measurements to be made throughout the cross-section of the acoustic beam. It is necessary to measure the sensitivity variation as well as the mean value. The indicated target strength distribution is broadened if the sensitivity changes significantly with the target direction. The theory of this effect is developed. A calibration technique is described which requires few measurements to achieve good accuracy. For the ES400 echo-sounder, measurements at 30 points in the beam determine the mean sensitivity to ± 0.5 dB or better. The sensitivity measurements of a particular transducer and echo-sounder varied over a 3 dB range. Reasons for this unexpected variation are discussed

A summary of target strength observations on fisheries from the shelf off West Africa

Abstract only. Journal home page: http://scitation.aip.org/jasa

Hydroacoustic performance of fishery survey instruments

Abstract only. Journal home page: http://scitation.aip.org/jasa

Some pitfalls of short-range standard-target calibration

Often it is necessary or desirable to perform a standard-target calibration at rather short range, for example, because of shallow water or interest in measuring animals at short range. A number of general range-dependent effects may prove especially troublesome at short range. These include effects connected with (1) time-varied gain or similar range compensation, (2) finite size of the target, and (3) pulse repetition frequency. The origins of these effects are reviewed and, where particular to a specific system, illustrated by reference to the SIMRAD EK500 echo sounder

Etterlatte oljeplattformer som kunstige fiskerev

Prosjektet som beskrives i rapporten har til hensikt å belyse i hvilken utstrekning etterlatte plattformer i Nordsjøen samler fisk, og om de kan utnyttes til lønnsomt fiske. Hoveddelen ble utført ved Albuskjell 2/4 Fox ved Ekofisk sommeren 1998. Fiskeforekomstene rundt plattformen ble kartlagt ved hjelp av akustisk mengdemåling fra forskningsfartøy og plattfarm, fangstforsøk med trål og garn,undervannsfilming og akustisk merketeknikk. Det konkluderes med at etterlatte plattformer samler fisk og dermed virker som kunstige fiskerev. Fangstpotensialet er ikke godt nok dokumentert, men resultatene fra undersøkelsen tyder på at det kan stå betydelige mengder fisk, særlig torsk, under en slik plattform. Etterlatte plattformer brukt som kunstige fiskerev vil dermed kunne bidra til å øke lønnsomheten i torskefiskeriene i Nordsjøen