lenochs%drcoa1.decnet@drcvax.af.mil (DRCOA1: :LENOCHS) (05/31/91)
From: "DRCOA1::LENOCHS" <lenochs%drcoa1.decnet@drcvax.af.mil> A short comment on KTO Rules of Engagement regarding FLIR contacts. Much of the fighting was done at night using either radar, IR or low light TV. Of course they were firing on targets I.D. by FLIR. The primary reason for coming home on a lousy day with a plane loaded with ordinance was inability to see and avoid all the nasty metalic/explosive things the enemy tends to throw at you. Anyone have data indicating how much FLIR sensors are degraded by various atmospheric conditions? Rick Lafford Eastman Kodak lafford@serum.kodak.com Opinions, what opinions?
anderson@erim.org (Rod Anderson) (06/04/91)
From: anderson@erim.org (Rod Anderson) lafford@serum.kodak.com (Rick Lafford) writes: >Anyone have data indicating how much FLIR sensors are degraded >by various atmospheric conditions? I don't have any data on actual Desert Storm atmospheric conditions, but perhaps the following general comments apply. Most military FLIRs operate in the long wave infrared, from 8 to 12 micrometers. Water vapor is the dominant absorber in this band, although carbon dioxide and other gases contribute some. To first order, FLIR performance is inversely related to absolute humidity, the total amount of the dominant absorber along the line of sight. Given that this amount was probably very small under DS conditions, good propagation would result. Other effects could be important, however. Scattering by atmospheric aerosols (dust, sand, salt, etc.) can be a significant source of extinction. The degree of extinction is a function of the optical properties of the aerosol, its size distribution, shape, and extincted wavelength of interest. For small particles (less than .1 wavelength) the scattering is proportional to the inverse fourth power of the wavelength. (The familiar Rayleigh scattering case.) Wind-blown sand (of say, 1-4um) which would obscure visual detection at 0.5 um would be much less of a problem in the 8-12um band. Another effect of atmospherics on performance is the target source signature. For example, high cloud cover would affect the solar loading on a vehicle, and thus its thermal signature. Note that this is independent of atmospheric absorption along the line of sight. Clouds along the line of sight are another matter. Unless they are VERY thin, don't count on seeing through them, in spite of the 1/4th dependence. A comparison of weather data from DS with Central Europe would be very interesting. Lack of all-weather has always been a serious criticism of FLIRs. I wonder how Desert Storm will change the conventional wisdom. -Rod Anderson
nanis@llex.ll.mit.edu (Jeff Nanis) (06/04/91)
From: nanis@llex.ll.mit.edu (Jeff Nanis) anderson@erim.org (Rod Anderson) writes: >I don't have any data on actual Desert Storm atmospheric conditions, >but perhaps the following general comments apply. Although I doubt it reached conditions like Central Europe, they were getting a good deal of rain at times over there. -- Jeff Nanis nanis@ll.mit.edu An official opinion? Not on my life.