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Lynn, That is very interesting...Thank you. David Bartsch From: LynnDarnel@aol.com Date: Wed, 27 Aug 2008 10:14:57 -0400 Subject: Re: [PSUBS-MAILIST] sonar question To: personal_submersibles@psubs.org Dave: Side scan sonar is usually a horizontally aimed phased-array sonar system. I have not seen the latest technology, but I have worked with side scan sonar in the past. The unit itself is a towed, torpedo-shaped, device with a row of transducers on each side. It transmits sound pulses out and records echo intensity. It does not observe things in 3-D, but effects like sonic shadows behind tall objects allow a trained operator to determine that something is sticking out of the bottom and approximately how tall it is. The shape of things is not always clear in 2-D unless you get the right view. Example: An upright sailboat seen from the stern might look like a block with a stick in the top. A perpendicular view from either side, however, would present a clear view of the hull profile from which you can calculate length (knowing travel speed) and height (from the cast shadow). Operation of side scan is a lot like looking out a distorted vertical slot on each side of a submarine. What you see instantaneously doesn't mean much, but if you record what you see and show it all at once you get a reasonable horizontal view. The effective width of the sound beam, horizontally, is very narrow like viewing through a vertical slit. The vertical spread of the beam is essentially from top to bottom. The vertical pattern is such that it does reflect off the bottom giving a good indication of altitude of the side scan. The sound also reflects off the surface, in shallow water, presenting clutter in the images. I hope that helps. Lynn Darnell ************** It's only a deal if it's where you want to go. Find your travel deal here. (http://information.travel.aol.com/deals?ncid=aoltrv00050000000047) Be the filmmaker you always wanted to be—learn how to burn a DVD with Windows®. Make your smash hit |