Deadzone Height Calculation
The distance from the bottom at which there is a bias (H_{BotBias}) associated with both processes therefore depends on pulse duration, angle to the fish, and depth (see Ona and Mitson 1996) as follows:


[17] 
where
BD = Bottom depth
θ = angle of fish location relative to the acoustic axis
c = sound speed in m•sec^{1}
τ = pulse duration in sec
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 7^{o} 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 halfpower beam angle of 11^{o}. Ona and Mitson (1996) present the theory of nearbottom echo integration as well as the equations needed to correct of this bias.
If sampling to a depth of 100 m using a 120 kHz with a 7º transducer, then:
and
S_{v} values from within 0.5 m of the bottom are biased