In a message dated 10/01/1999 7:13:12 AM Central European Daylight T,
> monty@arcadia.turner.com writes:
> On Fri, 1 Oct 1999, Andrew Martin 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 indetify them by type. My immediate reference
for this is Army Technology's Apache entry at
<http://www.army-technology.com/projects/apache/index.html> under the
heading of Missiles ("The Longbow fire control radar incorporates an
integrated radar frequency interferometer for passive location and
identification of radar emitting threats. An advantage of millimetre wave is
that it performs under poor visibility conditions and is less sensitive to
ground clutter. The short wavelength allows a very narrow beamwidth which is
resistant to countermeasures.").
And now, back to your regularly scheduled selection of GZG
product/settings/rules debates.
> Christopher Ruhl wrote:
I'm pretty sure the radar is active but incorporates a passive receiver system
as your following quote points out:
> My immediate reference for this is Army Technology's Apache entry at
Note that the radar _incorporates_ the interferometer? Basically
it can "hear" radar "pings", a passive sensor. With the interferometer, it
can then give an angle/bearing to the source of the ping, much like
knowing where a sound comes from, when using your ears.
> An advantage of millimetre wave is that it performs under poor
Here's what the radar send out, when it goes active, MMW.
So basically the radar is in passive mode "listening" for opposing radar
"pings". When in active mode, the radar sends out a "ping" of MMW energy in
the desired arc and "listens" for echoes. The MMW Hellfire is ARH, but, I
believe, it can travel along a bearing, flying blind, so as to minimise enemy
response time to the active radar homing "pings" the missile itself can send
and receive.
> On Sat, 2 Oct 1999, Andrew Martin wrote:
> Christopher Ruhl wrote:
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