Simrad ER60, Operator'S Manual

Page: 47 / 182

Operational procedures
39
850-164692 / Rev.B
In order to allow the echogram to indicate the depth where the
selected back-scattering is reached, make the following settings:
•
In the Echogram dialogue box, set Backscatter = Sv
(20 Log TVG).
•
In the Colour Scale dialogue box, set the desired lower Sv
limit.
Example: If the desired lower Sv limit is -70 dB, and at the
same time a signal-to-noise ration of 10 dB is required, the
setting in the
Colour Scale dialogue box for 20 log TVG
must be -80 dB . The depth where the light grey colour
appears on the echogram then indicates the maximum depth
where the desired
Sv limit is obtained with a signal-to-noise
ratio of 10 dB.
When you select Backscatter = Sp (40 log TVG) in the
Echogram dialogue to record single object target strength, the
desired lower TS limit has to be set in the same way as above.
Example: If the desired lower TS limit is -50 dB, and at the
same time a signal-to-noise ratio of 10 dB is required, the
setting in the
Colour Scale dialogue box for 40 log TVG
must be -60 dB . The depth where the light grey colour
appears on the echogram then indicates the maximum depth
where the desired lower
TS limit is obtained with a
signal-to-noise ratio of 10 dB.
When the trial has been completed, the corresponding noise
level in dB re 1
µ
Pa can be calculated for the described
procedure.
The instantaneous background noise is based upon one single
echo sample out of a fixed number of equidistant echo samples.
λ
Wavelength = c/f
c Speed of sound (m per sec)
f Frequency (Hz)
G Transducer gain (dB)
SaCorr Sa correction value (dB)
The current transducer gain is found in the Transducer
Parameters dialogue box.
Print the next table, and use it to fill in the measured values.