Now showing items 1-10 of 132
Digital representation of split-beam-transducer beam patterns
(ICES CM Documents;1986/B:2, Working paper, 1986)
The farfield beam pattern of each of two different split-beam transducers is computed and represented in the axial region by a finite number of constant levels. The accuracy of representation is determined as a function ...
Cylindrical sonar design for fish echo surveying
(ICES CM Documents;1988/B:3, Working paper, 1988)
Most applications of echo integration involve use of a fixed single-beam transducer that is rather narrow and downwards-oriented. It is often desired to sense fish in other directions, for example, to assess components ...
Summary of methods for measuring fish target strength
(ICES CM Documents;1988/B:4, Working paper, 1988)
Methods for measuring fish target strength are intercompared. The consistency of results obtained on the same or related species by different methods is noted.
Target strengths of Antartic krill (Euphausia superba)
(ICES CM Documents;1988/B:6, Working paper, 1988)
Encaged aggregations of swimming krill have been measured at 38 and 120 kHz. The results indicate that the target strength values are substantially lower than previously assumed.
Acoustic sampling volume versus equivalent beam angle
(ICES CM Documents;1988/B:5, Working paper, 1988)
Irnprovements in target strength measurement have shown the equivalent beam angle (EBA) to be a worrisome source of error in echo integrator surveys. The reason is that the EBA is generally defined as a purely physical ...
Designing an improved transducer array geometry
(ICES CM Documents;1988/B:2, Working paper, 1988)
Improvements in a split-beam transducer that is also used for surveying are sought through changes in array geometry. These are assessed through relative changes in the sum of source level and voltage response and the ...
Simultaneous two-sphere two-transducer calibration
(ICES CM Documents;1990/B:23, Working paper, 1990)
When directional transducers are mounted nearby, the central lobes of their beam patterns may partly overlap at ranges typical for standard-target suspension in calibration exercises, e.g., 20 m. According to the ...
Equivalent beam angles for several standard transducers
(ICES CM Documents;1990/B:21, Working paper, 1990)
Nominal values for the equivalent beam angle are given for several transducers. These are the standard split-beam transducers designed for the SIMRAD EK500 scientific echo sounder, with operating frequencies of 38 and 120 ...
Bad-weather calibration of split-beam echo sounder systems
(ICES CM Documents;1990/B:22, Working paper, 1990)
A condition for standard-target calibration is stability of the sonar platform and target rig. This condition cannot always be met, nor need it be when the transducer has a split-beam function. Since the position of ...
Definition of the problem of estimating fish abundance over an area from acoustic line-transect measurements of density
(ICES CM Documents;1990/D:25, Working paper, 1990)
The problem of acoustic abundance estimation is briefly reviewed. Under proper conditions, fish density can be measured with high accuracy along line transects. Observed variations in fish density consequently reflect ...