Optimal acoustic beam pattern corrections for split beam transducers
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http://hdl.handle.net/11250/104697Utgivelsesdato
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Precise in situ target strength estimates of fish can only be
made when the effect of the transducer directivity is totally
removed from the recorded target amplitudes. By guiding a
standard calibration target through the acoustic beam while
simultaneously recording the amplitudes and angular positions
of the target, a precise reconstruction of product of transducer
transmit and receiving directivity can be made. From several
thousand point measurements taken in a cross section through the
acoustic beam, the recorded data have been fitted to a
generalized three dimensional model by the use of non-linear
estimation. The suggested model functions yield very low residual
beam correction error with 95% of the data within ± 0. 5 dB.
Within the half power points of the beam, the residual beam
correction error is close to the observed ping to ping system
stability of ± 0.1 dB. The precision and repeatability of the
method is demonstrated through data from four split beam
transducers mounted on four different research vessels. These are
three ES-400 transducers and one EK-500 transducer, all working
on 38 kHz.