Simrad EY500, Instruction Manual

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Simrad EY 500
12
P3403E/A
M
M 9
'
4
U 2
0
6
9
(17)
M
M $
'
m
U
2
U
1
M
M 9
GU
(18)
$
' PHDQ
[
M
M $
] (19)
individual tracking of several potential bottoms simultaneously. For example,
bottom return number one could be from a large school of fish, return two from
the true bottom, and return three could be the echo which has travelled twice
up and down between the surface and the bottom.
In conjunction with echo integration it is vital that the bottom return is not
included in the integration process. After bottom detection, therefore, an
algorithm is activated which decrements the detected depth in small steps until
the received echo signal has vanished. Experience has shown that this last
technique substantially improves echo integration near the bottom. However,
it should be observed that for an inclined bottom the detected depth tends to be
slightly shallower than the true depth along the transducer axis.
5 BOTTOM RANGE
Bottom range is available on the display and on the printer and allows the
echogram relative to detected bottom to be shown with a resolution different
from that of the main echogram. This feature is useful when studying soft
sediment layers and bottom consistency. Waves propagating down into the
bottom are strongly attenuated, and echoes from subbottom layers are soon
below the dynamic range of the echogram colour scale. Hence, additional
amplification (performed in software) brings these echoes into the visible range.
Excess amplification is set from the menu system in dB’s per meter below the
detected bottom. A typical value would be 0.5 dB/m. However, the optimum
value will depend on bottom type and frequency and should be found
experimentally.
6 ECHO INTEGRATION
The method of echo integration is recognized as an efficient and reliable
technique for fish stock assessment. The EY 500 performs integration within
independently set depth layers. Basically, the integrator performs integration
in the vertical direction within the layers and averaging in the horizontal
direction along the path travelled by the vessel. The integration process is based
on the quantity 10log(S
v
) and is defined by the equations 17, 18 and 19: