Simrad SH40
Layers and deflections
Your sonar operations may also be disturbed by environmental situations that you are unable to control. Two typical conditions are temperature and salinity layers, and deflections caused by increasing or decreasing water temperature.
Temperature and salinity layers
You may experience that temperature and/or salinity layers exist in the water column. Since the speed of sound in water depends on its temperature and salinity, such layers will cause the sound beam to be reflected.
A
B
(CD015005F)
If you transmit a sonar beam down towards a temperature or salinity layer (A), it will be reflected as indicated in the illustration. The school of fish (B) you thought you would see will not be visible at all.
Deflections
On warm days — especially during summer — the sea surface will be heated by the sun, and the water temperature will gradually decrease with increasing depth.
36
B
A
(CD015005G)
When the temperature decreases (A) closer to the bottom, the sonar beam is deflected down as indicated by the illustration. The school of fish (B) you thought you would see is not visible at all.
302656/A
Basic theory
On cold days, you may experience the opposite: the cold water will be close to the surface, and the water temperature increases with increasing depth.
A
B
(CD015005H)
When the temperature decreases (A) closer to the surface, the sonar beam is deflected up as indicated by the illustration. The school of fish (B) you thought you would see is once again not visible at all, and you will also see a ring of surface echoes.
302656/A
37
ISBN-10: 82-8066-067-4
ISBN-13: 978-82-8066-067-4-1
© 2006 Simrad
Simrad AS
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P.O.Box 111
N-3191 Horten,
Norway
Telephone: +47 33 03 40 00
Telefax: +47 33 04 29 87 www.simrad.com
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