Re: Radar, sonar and more

On Thu, 24 Feb 2000 12:38:26 -0800 (PST), Cleats Balentine writes:
>I'm working on a scenario inspired by a recent report
>I heard on NPR about the ocean of Europa ... it's
>still in the embryonic stages of development.
>
>Anyway, I need some help that I'm hoping some listers
>might be able to provide:
>
>No. 1 Is there any naturally occurring element that
>can block radar? Is there any elemnet hypothesized or
>in hard sci-fi literature that can do this?
>Essentially what I'm looking for is something that can
>refract radar and prevent accurate readings.

Sure.  Lots of dirt.  Hills are good at blocking an amazing range of
EM radiation.  Do you want something smaller?  steel blocks radar
fairly well I seem to remember.  Mostly because it reflects it like
crazy, so you get a good return on the steel, but not on anything
behind it.  Really, radar penetrates things fairly poorly, so just
about anything will block and reflect it. 

Now, if you want to absorb the radar so you get no returns, its a
little harder.	I believe water absorbs radar pretty well, as do some
new plastics and such.

>No. 2 Will an abnormally loud aquatic environment
>prevent the effective use of sonar?

Maybe.	There are two general forms of sonar detection, active and
passive.

Passive is just listening for sounds that sound unnatural.  If the
background is loud and random, but there is still a repeating man made
sound in there, you may well be able to find it, if the random
sampling isn't so much higher amplitude that the man made sound is
reduced to noise.

Active sonar is where you send out a loud "ping" and listen for the
echos.	If the background is loud enough, it might be hard to hear the
ping when it comes back, but in general you should be able to tune the
frequency of the ping so that you can listen to a very tight frequency
range and eliminate most of the noise.	

Does that help?

-=- Matthew L. Seidl		email: seidl@cs.colorado.edu		
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