Re: [PSUBS-MAILIST] Re: SONAR

["Matt Cadieux" <compkid15@earthlink.net>]

The change of medium is correct but the hitting against the air would
"Bounce" SOME of the signal back and a normal fish finder will probably not
work with the transition from water to air.  I tried it on a robot I built.
I very precise sonar may work but one of the regular ones most people have
won't detect enough of the change.  I'll find out for sure for you.
----- Original Message -----
From: "Ed Greany" <crest25@attglobal.net>
To: <personal_submersibles@psubs.org>
Sent: Sunday, August 12, 2001 8:07 PM
Subject: Re: [PSUBS-MAILIST] Re: SONAR


> Yep, you're correct. Sonar will bounce or deflect with a change in
> medium or gradient temperature layer. I didn't comment about it bouncing
> or now off the surface since I have never tried that. I only know about
> signals going down or out from the vessel.
>
> Ed
>
> Adam Lawrence wrote:
> >
> > I don't know much about sonar but I do know about ultrasonics with
respect
> > to UT or weld inspection. When sound moves through steel,  plastic, or
> > whatever it moves at a relatively uniform velocity for the specific
medium.
> > When the sound wave reaches a point where the medium changes, like air
on
> > the other side of the steel plate, most of the wave is reflected back to
the
> > source. I would think that sound would reflect off the bottom and off
the
> > surface in a similar manner since a change in medium (velocity) has
> > occurred. As far as the sonar device needing to be calibrated for that
> > application, I don't know.
> > Adam L.
> > ----- Original Message -----
> > From: Matt Cadieux <compkid15@earthlink.net>
> > To: <personal_submersibles@psubs.org>
> > Sent: Sunday, August 12, 2001 10:21 PM
> > Subject: Re: [PSUBS-MAILIST] Re: SONAR
> >
> > > In order for a sonar to work it has to "hit" against something and
bounce
> > > back so an upward facing sonar would only give you readings if you
were
> > > under something.  SO it would only really be good to check when your
> > > surfacing to make sure that your not coming up under a boat other then
> > that
> > > it would give no reading.
> > > ----- Original Message -----
> > > From: "Ed Greany" <crest25@attglobal.net>
> > > To: <personal_submersibles@psubs.org>
> > > Sent: Saturday, August 11, 2001 3:13 PM
> > > Subject: Re: [PSUBS-MAILIST] Re: SONAR
> > >
> > >
> > > > Good question. The answer is no, now unless they are both on the
same
> > > > frequency.
> > > > The received is tuned to receive a certain frequency (range) and it
is
> > > > listening for its own bounce.
> > > > It's like two radio operators standing next to each other talking to
> > > > someone on the other end. The two radios do not mix and confuse the
> > > > receivers.
> > > >
> > > > Ed
> > > >
> > > > Michael B. Holt wrote:
> > > > >
> > > > > What problems appear if one uses TWO fishfinders: one pointed down
to
> > > > > give distance below the keel and one pointed up to give distance
to
> > > > > the surface?  Would the two interact to produce false readings?
> > > > >
> > > > > Mike
> > > >
> > >
>