Texas A&M University
Department of Oceanography
Sound frequency: How low can you go?
Side-scan sonars and multibeam echo sounders each use
different sound frequencies for different applications.
The higher the
instrument's sound frequency, the smaller the wavelength -- and the greater
the detail of the final image of the seafloor. For example, in seawater,
the wavelength of a 12 kHz sound wave is 12.5 centimeters, but the wavelength
of a 500 kHz wave is only 0.3 centimeters. The higher freqency would give
a much better image of the seafloor.
But the trade-off is that high frequency sound weakens
more rapidly as it travels, so distant targets require lower frequencies.
More (below)
Deep-ocean sonars typically use frequencies in the 12-30 kHz range, whereas shallow water sonars use 100-1200 kHz. Also, the size of the towfish is related to wavelength: The longer the wavelength, the bigger the towfish. A 12 kHz side-scan sonar towfish would take up a moving van. A 500 kHz unit will fit nicely in the backseat of your car.
-- Will Sager
http://oceanography.tamu.edu/Quarterdeck/1998/3/sager-geometry.html
Copyright 1998-1999, Department
of Oceanography, Texas A&M University.
Updated November 24, 1998. (abdw)
Send Quarterdeck inquiries to quarterdeck@ocean.tamu.edu.
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