Simrad ES80 Reference Manual page 465

http://en.wikipedia.org/wiki/Signal_to_noise_ratio (September 2013)
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 may be divided into the following
types of noise:
• Self noise
• Ambient noise
• Electrical noise
• Reverberation
• Fishing gear noise
The transducer can pick up noise from
A
• Biological disturbances
• Interference
• Cavitation
• Propeller noise
• Flow noise
• Acoustic noise from other hydroacoustic systems
The transducer cable is long, and may pick up electric noise from generators,
B
pumps, cooling systems and other electric or electromechanical devices.
The preamplifiers are very sensitive, and they can easily pick up electrical noise
C
from internal and external power supplies. The preamplifiers are also vulnerable for
analogue noise created by their own electronic circuitry. Digital noise created by
the converter and processing circuitry can also create problems.
D Converters transform the analogue echoes to digital format.
Signal processing circuitry can create digital noise.
E
406273/C
Concept descriptions
463