Frequency/period Limits for the AWAC
There is a direct relationship between the deployment depth of an AWAC and the limit on the measureable wave frequency (or period).
The physical phenomena controling this is discussed in a previous forum entry for the direction limits. If you wish to learn more about why
this happens then jump here:
AWAC directional wave frequency limits Principle
The nondirectional frequency limit is a limit imposed by the Acoustic Surface Tracking (AST). This limit has to do with size of the ensonified AST footprint
on the sea surface relative to the measurable wavelength. We use a Nyquist-like logic, whereby the measureable frequency is when the diameter of the footprint is equal to half a wavelength. Any wave smaller than this will be more or less unmeasureable. The size of this circular footprint is determined by the (a) the beam width and (b) the distance from the sea surface. The size of the footprint will increase with wider beam width or with the greater the distance from the sea surface.
Fortunately, the beam width is only 1.7 degrees, so this means the AWAC can be deployed at surprising great depths without sacrificing wave information.
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