From: James Rogers (jamesr@best.com)
Date: Mon Mar 20 2000 - 12:39:01 MST
On Mon, 20 Mar 2000, Michael S. Lorrey wrote:
> Joe Dees wrote:
> > The test actually works AGAINST the agent-firing hypothesis, as in
> > the FLIR recreation, people are visible next to all the fired weapons,
> > whereas in the original FLIR, no contiguous people are visible. Guns
> > do not kill people unless other people are firing them, and such people
> > being visible in EVERY instance of the "recreational" gunfire, but in
> > NO instance of the original glints, the test results do not bode well
> > for the contentions of the Branch Davidians' attorney that such glints
> > represent gunfire.
>
> Another reason why the people may show up in this footage and not in
> the original footage is that the ambient temperature and ground
> temperature on the day of the original incident were very close to human
> body temperature, while the recreation film was shot at temperatures of
> 69 degrees, a 30 degree difference. Additionally, there was not a fire
> going in the recreation to dampen the sensitivity of the FLIR at low
> temperatures.
Michael is right on the money for this one. Humans and other animals will
quickly disappear into the ground clutter as the ambient temperature
approaches their normal body temperature, particularly if they are
stationary. The practical effect is that the effective resolution of
human objects drops as the ambient temperature increases. In other words,
while it is easy to resolve a person a quarter 400m away when the ambient
temperature is 60F, you have to be practically on top of a person to
resolve them when the temperature is 90F. In my own experience (using IR
in a search mode), IR is almost useless on warm summer days because you
have to get so close that you can see what you are looking for without the
IR. It works great at night, though.
Gunfire on the other hand, is always much hotter than ambient.
> All of these factors, as well as the use of dyes and starches in
> clothing could be contributing factors in why the people's bodies showed
> up in the recreation, but not the original incident.
I don't think this is a factor, since FLIR is a passive technology.
As I understand it, the fabrics/dyes used in BDUs are non-reflective in the
IR spectrum so that you don't stand out when painted with an IR beam
(e.g. from near spectrum devices like night vision). You can't effectively
shield a person against far infrared e.g. FLIR. For hunters, there is a UV
issue with some detergeants and brighteners, since certain animals can see
into the UV spectrum.
-James Rogers
jamesr@best.com
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