Re: [OT] Longbow Hellfire (was Re: GMS Air)

On Sat, 2 Oct 1999, Andrew Martin wrote:

> Christopher Ruhl wrote:
>
> > I'll leave the final call to some of the brighter list members, but
> > from all the literature I've read on the Longbow system, the
> > millimetric-wave radar is a passive system.  I know it seems
> > contradictory, but it is supposed to detect the disturbances in
radio
> > frequencies caused by large masses like tanks and have the
definition
> > to identify them by type.
> 
>	I'm pretty sure the radar is active but incorporates a passive
> receiver system

i remember reading about millimetric (mm) radar a while back. this was
in
the 'new scientist', so it could all be complete bunk. also, my memory
is
a bit hazy. you have been warned.

the thing is, mm radio waves interact with water molecules as well as
metals. mm radio photons are of the same energy as the hydrogen bonds
between water molecules, or something. i would guess that the bonds
between atoms in metals (such as they are) are of a similar energy.

thus, water and metals emit them as part of their thermal radiation,
just
as they do IR (in fact, you can consider mm radio a sort of
infra-infra-red). thus, passive mm instruments can detect warm objects
containing water (eg people) or metal (eg tanks). 'warm' in this context
covers pretty much everything unless it's being seriously chilled.

anyway, the point is that you can build a passive mm radio imager, which
operates a lot like an IR camera. i remember a description of the image
of
a building: the people and metal fittings (pipes, cable ducts, etc), are
perfectly visible (as glowing blobs), and the concrete, plastic, etc is
transparent. it sounded pretty cool.

anyway, i could be totally wrong about all this: just as there are two
types of IR, there could be two types of mm radar.

if i'm right, then mm radar should function essentially like a tv camera
which only sees metal and wet things; you'd still need some intense
computing power to analyse the image and find the target. otoh, it might
be that metal and people are different 'colours', so they're easy to
distinguish.

oddly enough, i found nothing much on the web. there was this one
half-decent political link which mentioned some details:

http://wonderland.pasdex.com.au/~belgrave/the_expurgated.obey.html/x-ray
.htm

tom