Kongsberg Simrad SN90, Installation Manual

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Acoustic noise
As with any other hydroacoustic systems, the quality of the SN90 presentations are
subject to unwanted acoustic noise. The echoes from any large and small target must be
detected inside the noise.
It is important that we keep this noise level as low as possible in order to obtain long
range and dependable interpretations of the echoes. Even with the advanced noise
filtering offered by the SN90, we must address the noise challenge during both planning
and preparations for the SN90 installation.
Topics
Contributing factors, page 54
Self noise, page 56
Ambient noise, page 58
Electrical noise, page 58
Reverberation, page 59
Some means to reduce acoustic noise, page 59
Contributing factors
Several factors are contributing to the performance of the hydroacoustic equipment
used on board a vessel.
Such factors include:
• The quality and properties of the transmitted signal
• The quality of the receiving system
• The operational settings made during operation
• The properties of the target(s)
• The signal-to-noise ratio
The majority of these factors can neither be controlled nor improved by means
of installation methods or transducer locations. The quality and properties of the
transmitting and receiving systems are key factors during our product development, while
our end user documentation aims to help the user to make the right filter settings during
operation. As for the target properties, there is nothing any of us can do with those.
The signal-to-noise ratio , however, can be improved by making the correct choices
during installation.
Signal-to-noise ratio (often abbreviated SNR or S/N) is a measure used in
science and engineering that compares the level of a desired signal to the level of
background noise. It is defined as the ratio of signal power to the noise power, often
expressed in decibels. A ratio higher than 1:1 (greater than 0 dB) indicates more
Simrad SN90