Simrad EY500, Instruction Manual

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Simrad EK 500 / EY 500
P2260/E
5
1 THE PURPOSE OF CALIBRATION
The EK 500 and EY 500 are scientific echo sounders designed for quantitative
measurements, i.e. measurement of single fish target strength and
measurement of biomass backscattering coefficient. During the calibration a
reference target with a known target strength is lowered into the sound beam,
and the measured target strength is compared with the known target strength.
If it is necessary to adjust the echo sounder, this is performed by changing a
parameter in the mathematical equations in software. Since the echo sounder
is digital right from the receiver front end, there is no analog gain adjustment.
The reference target is normally a metal sphere. Simrad supplies copper
spheres, one for each frequency. The sphere diameter is selected for minimum
temperature dependence.
For acoustic surveys where accurate quantitative measurements are required
it is essential that the echo sounder is correctly calibrated. It is a safe practice
to perform the calibration before and after the survey. If experiences over time
show that no adjustments are necessary, it may be appropriate to reconsider the
need for frequent calibration. Simrad recommends that calibration is performed
at least once a year, and in areas with different summer and winter condition
at least twice a year.
In the following calibration procedure typical settings on the EK 500/EY 500 are
specified:
Ping Interval: 1 sec.
Transmit Power: Normal (applies only for EK 500)
Pulse Length: Medium
Receiver Bandwidth: Wide
Transducer Depth:
0.0 m
If other settings are to be used during the survey, the calibration should be
repeated for these.
A lobe program which can be supplied from Simrad makes the TS gain
calibration procedure a relatively uncomplicated task by using an extra PC
connected to serial line 1 in a split-beam system. This program will be
noncritical with respect to movement of the reference target sphere and it will
enable the inexperienced operator to obtain a good calibration result. This
program should be used whenever possible. This procedure is described in
chapter 3.