Re: Anti-armor mines!

At 04:15 PM 9/4/98 +1200, you wrote:
>As a further amendment to gravity gradiometers:
>In the June 1998 issue of Scientific American, page 58, third column,
first
>paragraph, I quote:
>    "Some of the resident engineers had thought of using these
sensitive
>meters to monitor the LOAD of passing trucks, ..."
>    My emphasis added.
>    A truck weighs 10 - 100 tons? It's load is 10 - 100 tons? A
submarine
>weighs 1000's of tons. A minefield is probably 100Kg to 1 ton. A 10 -
1000
>difference. It's not much for 200 years of technology advancement to
get the
>required accuracy to detect a minefield by it's gravity gradient.
>
Keep in mind that both gravity meter and gravity gradiometer readings
are 
interpreted to indicate variations in the local densities. The 
materials used to build a several thousand ton submarine are far 
denser than the surrounding seawater (roughly 7 times as dense, IIRC).
The difference in density between a mine and the surrounding 
substrate is much less. How could you tell the difference between 
a rock and a mine? I'm sure J.A. will correct me if I'm wrong, but 
most mines you would be looking for would be less than 10kg.

I'm not saying it's impossible, but I just think that the signal to 
noise ratio would be extremely low. Avoiding detection would simply
be a matter of matching the densities of the mine and the substrate.
This would make detection by gravimetric means _impossible_ since the 
mine would not change the local gravity field.

Cheers,

       Tony Christney
       acc@questercorp.com

  "If the end user has to worry about how the program was 
   written then there is something wrong with that program"
				  -Bjarne Stroustrup