Simrad EY500, Instruction Manual

Page: 226 / 262

Calibration
24
P2260/E
4 NOISE MEASUREMENTS AT SEA
The final result of the noise measurements should be a plot of the acoustic noise
in front of the transducer versus vessel speed. This plot may be compared with
similar plots for other transducers on the same vessel, or plots from other
vessels, and may thus serve as an evaluation of the transducer location and the
vessel noise radiation. In addition, the noise plot may be a guide in choosing the
vessel speed during acoustic surveys. Since the propeller pitch and revolutions
per minute influence the noise level, it is important to determine the most
favourable combination of these factors. Normally a slow rotation and a high
pitch give the lowest noise.
The noise measurements should take place at least one nautical mile off shore,
far from other ship traffic and and with favourable weather conditions. It is
preferable that the water depth is 200 m or more. The noise should be measured
at different vessel speeds, from 0 to maximum speed, with steps of 2 knots. The
vessel’s course must be kept steady during these measurements.
With the settings specified below, the printer will produce an echogram and an
integrator table. With some experience it should be possible to reveal the noise
source from looking at the echogram. Typical sources may be propeller
cavitation, small damages on the propeller blade, the machinery, or thermal
noise. It is a good routine to save the echogram with the integrator table for
comparison with later recordings.
Select the Operation Menu and set:
Ping Mode: Normal
Ping Interval: 0.0
Transmit Power Normal (only for the EK 500)
Noise Margin: 0 dB
Select the Transceiver Menu/Transceiver-1 Menu (if the transceiver to be tested
is transceiver No. 1) and set:
Mode: Passive
Pulse Length: Medium
Bandwidth: Wide
Select the Transceiver Menu/Transceiver-2 Menu and set (only for the EK 500):
Mode: Off
Select the Transceiver Menu/Transceiver-3 Menu and set (only for the EK 500):
Mode: Off