[PSUBS-MAILIST] Sonic Transmission in Shallow Waters

["Jens Laland" <laland@artematrix.org>]

Here is a summary from the book PHYSICS OF SOUND IN THE SEA (1969),
Chapter 6: "Shallow-Water Transmission" (i.e. sonic transmission, only):

In shallow water, a distinction must be made between transmission over
"mud" bottoms (which resembles deep-water transmission) and transmission
over all other bottom types. No significant differences has been
discovered in sonic experiments between any of the other bottom types,
including "mud and sand".

Over sloping bottoms, a significant dependence on refraction pattern has
been observed: with downward refraction transmission tends to be poor,
while in isothermal water it is as good as in deep water.

Over level bottoms, with isothermal water or in the presence of downward
refraction, the attenuation is very small for frequencies below 2 kHz
(ref., the HBH-2 should be operated below it's resonance frequency of 3
kHz).

In the portion of the sea fairly near to the surface, which is the region
of interest in sonic listening (in our case), the absorption coefficient
probably depends on highly variable factors, such as bubble content; thus
large deviations may be expected to occur quite frequently.

There appears to be little correlation at sonic frequencies between
transmission loss and refraction conditions, depth of the water, and
surface roughness. With strong upward refraction, an increase of
attenuation with increasing sea state has been observed, undoubtedly
caused by the poor reflectivity of a rough and aerated surface.

At short ranges, out to approximately the range equal the depth of the
water, image interference maxima and minima have frequently been measured.

Reliable information on sonic transmission is scanty and is less
consistent than the information on the transmission of sound above 20 kHz.

Sonic transmission has probably been a more difficult field for
investigation than supersonic transmission, because of the low directivity
of most sources of sonic sound.

Best regards,
Jens Laland






************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003.  Your email address appears in our database
because either you, or someone you know, requested you receive messages
from our organization.

If you want to be removed from this mailing list simply click on the
link below or send a blank email message to:
	removeme-personal_submersibles@psubs.org

Removal of your email address from this mailing list occurs by an
automated process and should be complete within five minutes of
our server receiving your request.

PSUBS.ORG
PO Box 53
Weare, NH  03281
603-529-1100
************************************************************************
************************************************************************
************************************************************************