Re: Radar, sonar and more

In a message dated 2/24/00 2:39:13 PM Central Standard Time, 
kevinbalentine@yahoo.com writes:

<< 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.
 
 No. 2 Will an abnormally loud aquatic environment
 prevent the effective use of sonar?
 
 Thanks in advance for any help you can provide. >>

1) Any thick natural surface will stop radar cold as it reflects the
beam - 
rock, trees, wooden walls - sufficent distance of thick vegetation any 
substance through whihc the beam will not pass is a "naturally occuring"

anti-radar device

If you mean purposefully used artificial substance we have chaff today -

which is a thin strip of mylar - preferably cut to the same physical
length 
as the wave length of the radar which sends back HUGE echoes to the
receiver 
effectively making any definition of possible targets impossible.

Background sound must be filtered out of passive sonar detection
systems, 
computers and the human ear are very good at doing this, but both
require 
time to evaluate the data. Echoes from active sonar are alos bollixed
fairly 
easily, though not always effectively, by bubble bursts and noise
makers, 
botto echoes and the like.