Kongsberg EM 712, Installation Manual

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nearly the same frequency. Interference effects can be observed with all types of
waves, for example, light, radio, acoustic, surface water waves or matter waves.
https://en.wikipedia.org/wiki/Interference_(wave_propagation), April 2016
Ambient noise
Ambient noise is usually not a limiting factor to the performance of sonars and echo
sounders.
The ambient noise may be split up as follows:
•
Sea noise
: Air bubbles, seismic disturbances, waves, boundary turbulence, etc.
•
Biological noise
: Fish, mammals
•
Man made noise
: Other vessels, interference
•
Precipitation noise
: Heavy rain or hail
In some areas, where many vessels operate together, the engine and propeller noise from
other vessels may be disturbing. Interference from hydroacoustic instruments located
in other vessels may also be a limiting factor. The sea noise depends on the weather
conditions. In bad weather the sea noise can be quite high due to the waves.
Electrical self noise
Electrical or electronic self noise is picked up or generated in any other part of the
equipment than the transducer.
Hum picked up by the transducer cables or picked up from the power supply is usually
the most common source of electrical self noise. At higher frequencies – where rather
wide bandwidths are necessary – the noise from components, transistors or other
analogue electronic may be a limiting factor.
Some means to reduce acoustic noise
Several factors are contributing to the performance of the hydroacoustic equipment
used on board a vessel. Careful planning of the EM 712 installation may reduce the
acoustic noise.
Unfortunately, it is impossible to simply provide a number of specific procedures to
reduce the noise.
An important factor is the physical location of the transducers. This depends on the
vessel's design and construction, how the hull is shaped, and how the water runs along
the hull. Other factors deal with other equipment mounted on board, and this will also be
vessel dependant. At moderate ship speeds the machinery noise is usually dominant. At
medium speeds the flow noise increases more rapidly and takes over, while at higher
speed the propeller noise will be the main contributor.
Kongsberg EM 712 Installation manual