Self Noise - Kongsberg Simrad SX90 Reference Manual

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. Electric noise from generators, pumps, cooling systems
B
and other electric or electromechanical devices is easily picked up.
C The preamplifiers are very sensitive. They can easily pick up electrical noise from
internal and external power supplies. The preamplifiers are also vulnerable to analogue
noise created by their own electronic circuitry. Digital noise created by the converter
and processing circuitry can also create noise problems.
The converters transform the analogue echoes to digital format.
D
Signal processing circuitry can create digital noise.
E
Related topics
Improving the recognition of fish and schools using receiver filters, page 117
Concept descriptions, page 638
Acoustic noise, page 645

Self noise

Any vessel equipped with a hydroacoustic system (for example echo sounder or sonar) will
produce more or less self noise.
There are many sources of such self noise. It is necessary to analyse the different sources
of self-noise on a vessel, and find out how each source can affect the noise level of the
hydroacoustic instruments.
Machinery noise
The main contributor to machinery noise is usually the main engine on board the vessel. The
contribution from auxiliary machinery may, however, be considerable, especially if it is in
poor shape. The machinery noise can be transmitted to the transducer as:
• Structure-borne noise through the ship structure and the transducer mountings.
• Water-borne noise through the hull into the water to the transducer.
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Concept descriptions
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