Kongsberg Simrad SN90, Installation Manual

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381298/C
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signal than noise. While SNR is commonly quoted for electrical signals, it can
be applied to any form of signal [...].
http://en.wikipedia.org/wiki/Signal_to_noise_ratio (September 2013)
For active sonar and echo sounder systems, the signal is the echo that we want to know
something about, while the noise is any unwanted signals or disturbances. The echo
must be detected in the noise and therefore it is necessary to keep the noise level is as
low as possible in order to obtain long range and dependable interpretation. The noise
that contributes to the signal to noise ratio on hydroacoustic instruments may be divided
into the following types of noise:
• Self noise
• Ambient noise
• Fishing gear noise
• Electrical noise
• Reverberation
(CD010205_900_001)
A The transducer can pick up noise from
• Biological disturbances
• Interference
• Cavitation
• Propeller noise
• Flow noise
• Acoustic noise from other hydroacoustic systems
B The transducer cable is long, and may pick up electric noise from generators,
pumps, cooling systems etc.
C
The preamplifiers are very sensitive, and they can easily pick up electrical noise
from internal and external power supplies. They are also vulnerable for analogue
noise created by their own circuitry. Digital noise created by the converter and
processing circuitry can also create problems.
D
A/D converters transform the analogue echoes to digital format.
E Signal processing circuitry can create digital noise.
Preparations