We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
Real-time calibration of in situ measurements of target strength.
- Authors
MacLennan, David N.
- Abstract
MacLennan, D. N. 2011. Real-time calibration of in situ measurements of target strength. – ICES Journal of Marine Science, 68: .The in situ measurement of target strength (TS) depends on exactly one fish being within the sampled volume. This is more likely to occur the nearer the transducer is to the fish targets. The detection rate can be improved by lowering the transducer on a cable from a stationary vessel, so decreasing the range to the observed fish. In this application, a standard sphere is commonly suspended below the transducer to provide the real-time calibration of the received signals. However, forward scattering by the sphere distorts the transmitted pulse, and equally the returning fish echoes, causing a bias in the estimated TS. Further, for a split-beam transducer, forward-scattering of the fish echo by the sphere modifies the phase differences observed between the transducer segments. This changes the apparent distribution of targets, but not the estimated TS. The biases are not large, those considered being within ±0.9 dB, and they depend on the sonar frequency, the target range, and the direction. The theory of these effects is examined, and formulae are provided for correcting the observed fish echo to that which would be received in free-field conditions, i.e. with the sphere removed.
- Subjects
FISHES; FISHERIES; FISHERY management; FISH management areas; TRANSDUCERS
- Publication
ICES Journal of Marine Science / Journal du Conseil, 2011, Vol 68, Issue 3, p626
- ISSN
1054-3139
- Publication type
Article
- DOI
10.1093/icesjms/fsq172