Simrad EY500, Instruction Manual

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Simrad EY 500
14
P3403E/A
PORT STARBOARD
FORE
AFT
(CD469)
FP
AP
FS
AS
Figure 3 Split-beam transducer.
7 SPLIT-BEAM OPERATION
Observation of fish with the EY 500 is based on echo integration for assessment
of the total biomass and the split-beam technique for assessment of the size
distribution of individuals. Thus, the split-beam feature represents a valuable
supplement to echo integration.
.
A split-beam transducer is electrically divided into four quadrants as shown in
figure 3. All four quadrants are excited in parallel during transmission.
However, the received signal from each quadrant is amplified separately in a
four-channel matched receiver allowing the direction of arrival of an echo to be
determined. An acoustic wavefront propagating towards the transducer arrives
at different times at the four quadrants causing the phase angle of the electrical
output signal from the quadrants to differ. The fore-and-aft angle is determined
from the electrical phase difference between the fore and the aft transducer
halves (the FP+FS signal relative the AP+AS signal), and the athwartships
angle from the starboard and port signals (the FS+AS signal relative to the
FP+AP signal). The ratio between the electrical and mechanical angle is
referred to as the "angle sensitivity" of the transducer (see table under
Transceiver Menu in section "Operation").
In figure 4 fish "A" is positioned along the transducer axis where maximum
transducer gain occurs, and fish "B" is positioned towards the edge of the beam
where the gain is lower. Evidently, the echo signal from fish "A" will be stronger
than the signal from fish "B" even though they are of the same size and at the
same depth.