Deadzone Height 1.0

The distance from the bottom at which there is a bias (HBotBias) associated with both processes therefore depends on pulse duration, angle to the fish, and depth (see Ona and Mitson 1996) as follows:<br />eqn17 [17]<br /><br />where<br /><br />BD = Bottom depth<br /><br />?zN* = angle of fish location relative to the acoustic axis<br /><br />c = sound speed in m*sec-1<br /><br />?Ya*z = pulse duration in sec<br /><br />Here this is calculated for the half- power beam angle as an indication of distance from the bottom where we can expect a bias. For a typical 7o transducer operating with 0.4 msec pulse length, the HBotBias is 0.5 m at 100 m depth (see example below). This increase to 0.76 m with a half-power beam angle of 11o. Ona and Mitson (1996) present the theory of near-bottom echo integration as well as the equations needed to correct of this bias.<br /><br />If sampling to a depth of 100 m using a 120 kHz with a 7?*N* transducer, then:<br /><br /><br />eqn17.1<br /><br />and<br />eqn17.2 <br /><br />Sv values from within 0.5 m of the bottom are biased

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