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From: Ken James (no email)
Date: Fri Jun 02 2006 - 02:57:21 EDT
The issue of semi-submerged containers does not seem to me to really be an
issue - lets see - containers are 12 feet or so minimum in an dimension -
when containers are really going to be an issue, I would be most probably in
deeper water, thus getting pretty goog forward range - specified as AT THE
SURFACE - but the container is 12 feet down - seems to me I would see it
pretty good!
Reply;
This is not a correct conclusion. The fact is all the fwd scan units depend
on a depth of water to see fwd, in other words they cannot see the surface
(unless maybe they bounce a beam off the bottom and the reflection bounces
back...). The deep water is needed to see fwd as the beam angles out as a
conical or elliptical beam and the angle makes it spread down as it goes
fwd.
As far as I know, it is not technicaly possible with sonar to spot an object
right on the surface because as the beam travels to the air water interface
it gets refracted and reflected and so becomes useless.
I think the container depth of 12 ft would only be see-able if the boat was
very close. By that time it is too late.
Of course if you are a sub looking up it would be different.-Ken
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