Re: Advantages Of FLIR Vs. NVG Image Intensification Systems ?

On Thu, 24 Nov 2005 12:29:38 -0500, "Robert11"
<rgsros@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

>Can someone please summarize for me the major differences between a FLIR
>system vs NVG (image intensification) ?

The terms FLIR and NVG refer to how they're used. FLIR is
vehicle-mounted (tank or plane) NVGs are big heavy spectacles. Either
can use any of the three generations of technology. It's the tecnology
that makes the fundamental difference in capabilities.

1st generation begin in WW2. They used simple image conversion tubes to
take a bright (but invisible) image produced by a large infra-red
floodlight and transform it to a visible image. Their enormous drawback
is the need for an active illuminator, which makes a _massive_ target on
any battlefield.

They lasted into the '70s for tank sighting systems and the '80s as
convoy driving NVGs. Vehicles could be equipped with infra-red only head
and tail-lights, so that drivers with goggles could drive a convoy
whilst "blacked out". As these had less obvious active illuminators
than the tank sights, they remained useful for about a decade longer.

2nd generation were image intensifiers. These are the "starlight scopes"
that still need illumination to work, but can manage with a little
moonlight or leakage from the target's own lighting.

Modern retail "NVGs" can be of this type (the cheap ones are just 1st
gen). They still have military significance, particularly for personal
weapon sights. Their great advantage is their simplicity and
compactness, their drawback is the continuing need for a clear sight of
a dimly illuminated target.

3rd generation use long-wavelength infra-red, as is radiated by any watm
object, even without any illumination. They can literally "see in the
dark". Their other advantage is that these wavelengths are not absorbed
by cloud cover or smoke screens, as shorter wavelengths are.

Particularly for tank sights, this gave rise to a change in basic
tactics. A smoke screen is no longer a merely defensive measure to hide
behind, it can also cover an attack by vehicles that can see through it
to operate and to select their own targets.

The disadvantage is that these systems are still large and very
expensive. They require complex chemistry to make their sensor elements
and these elements are often fragile, sensitive to moisture or of
limited life.

As these systems are by their nature sensitive to any warm item, they
also need their optics to be actively cooled. This was originally done
by compressed gas and a Joule-Thomson cooler (the gas cools when
expanded through a small nozzle, the gas isn't "stored cold" itself).
Very few actually used a bucket of liquid nitrogen, as that's a logistic
nightmare in military service. More modern systems may use electric
coolers, providing longer active lifetimes in the field. The "field
useful cooling time" is a major constraint on their effectiveness.


As to resolution, then this is limited by the same old optical problems
of any other system. Big sensors have better resolution, bigger optical
systems relative to the sensor size give better sensitivity. If you can
afford it and carry it, then you can have big sensitive sensors - look
at helicopter-mounted systems or the business end of an A-6 targetting
pod.

.