From: Terry W. Colvin (fortean1@mindspring.com)
Date: Thu Jan 16 2003 - 19:47:29 MST
On Sat, 19 Jan 2002 17:41:02 -0700,
"Terry W. Colvin" <fortean1@mindspring.com> wrote:
>Subject: FWD (SK) Re: FLIR [Waco, Branch Davidians]
>
>A few weeks back I purchased Mike McNulty's latest video about the Branch
>Davidian debacle. The title is "FLIR," and it is another attempt by McNulty to
>portray the US forces as killers of innocent BDs.
<snip>
>John Blanton
>
>-------------------
>
>Here are some comments I have...
>
>>FLIR is an acronym that stands for Forward Looking Infra-Red. It's a
>>technology that uses far infra-red radiation for seeing without benefit
>>of visible light. Why it's necessary to add the words "forward looking"
>>is not clear, except that IR is not very satisfying as acronyms go, and
>>it's too much like a Spanish verb.
>
>My understanding is that FLIR is not an acronym for the technology, but for
>the specific devices themselves--infrared viewing pods attached to aircraft.
>They're literally "forward-looking infrared" cameras, to allow the crew to
>pick out details in the dark, so they can target weapons, gather
>information, navigate in bad weather, etc.
This is correct. FLIR is an acronym borrowed from the military, where
an infra-red sensor is mounted either in a pod or in the nose of an
aircraft and is used to image the field of view immediately in front
of the aircraft (the "forward looking" bit). So-called "FLIR"
installations mounted on police helicopters are not specifically
"FLIR" at all, but "steerable IR" sensors. To confuse things even
more, they are sometimes referred to as "FLIR Radars", when they're
not even radars either, which is entirely different (are you out there
and taking note, Sheriff John Bunnell??!).
Radar emits narrow beams of radio energy which are reflected off objects
in the field-of-view and detected by a receiving antenna. Actually,
"reflected" is not quite the true story, either, but I'll let that pass.
IR sensing is usually entirely passive - the IR detector only senses
IR radiation, it doesn't emit it, like using a flashlamp or a radar to
illuminate a field of view, though IR floodlights do exist (these act as
"stealthy floodlights", because if you don't have an IR sensor then
you can'see it). This is complicated to achieve and is not used very often.
IR is more correctly called "Thermal Imaging" (TI). This is the TI in
the acronym TIALD (Thermal Imaging and Laser Designation), which is an
integrated weapon aiming system that uses a thermal imager to view a scene
and detect targets, and a laser designator for so-called "smart" (terminally
guided) weapons (bombs or missiles). TIALDs are usually fitted to aircraft
in the form of an externally-mounted pod which contains a steerable turret
containing the TI sensor and the laser designator. Civilian police imaging
systems have borrowed this concept by having a steerable spherical turret
with windows in it though which the sensors view the outside world. The turret
usually also contains (or is slaved to) a powerful floodlight ("Night Sun",
for example.
The other "see in the dark" system is the Image Intensifier (II). This is
another entirely passive system, which takes available light (including a
small amount of infra red) and amplifies it several hundred times using a
device caled a photomultiplier.
Again, TV and film have mangled the technology. Most "thermal goggles" you
see in the movies are actually image intensifiers, which do not function in
daylight (you can damage the photomultipliers by exposing them to bright
light).
IIs do not function in total darkness, but do work in extremely low light
conditions ("cloud covered starlight" is the usually quoted lower limit
to their performance).
Both systems have advantages and disadvantages - TIs work in total
darkness, but don't resolve fine images. IIs show shadows and fine detail
such as power lines and vehicle tracks, but are overloaded by bright lights,
and so on. Where TIs are bulky and require weighty cooling equipment, IIs
are light and compact, often being the size of a pair of field glasses.
More sophisticated systems combine the two (a technique called "image fusion"),
with high-speed software to take the best bits of both systems to synthesise
a higher quality image. Image fusion can also combine data from other sensors,
including radar and visible-light cameras, and could feasibly include Ladar
(laser, that is, optical wavelength radar), sonar and so on.
TI's main use is to look for targets. Engines, exhausts and tyres on
vehicles that have recently been in motion show up as bright, hot spots
against the darkness of the cooler surrounding terrain. TI can (and is)
used during daylight as well as at night. TIs can spot artificial camouflage
against natural foliage, and can even see the difference between camouflage
improvised from foliage because cut and dying greenery has different thermal
properties to undamaged trees and bushes.
IIs are only used at night or in darkened building interiors. Their main
use is to aid a pilot in seeing the view outside the cockpit. Because IIs
are light and robust, they can be worn by individual troops moving and
fighting at night, and can be incorporated into gunsights.
IIs are not especially effective in poor weather, since they only apmplify
the available light. TIs are marginally better, but not much. Poor weather
is still the major factor in reducing the availability of aircraft to
assist other troops.
HTH
Robin Hill, STEAMY BESS, Brough, East Yorkshire.
--
Terry W. Colvin, Sierra Vista, Arizona (USA) < fortean1@mindspring.com >
Alternate: < fortean1@msn.com >
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