FROM: Andy Resnick SUBJECT: Re: A very basic FLIR question DATE: Thu, 23 Sep 1999 07:57:05 -0400 ORGANIZATION: NASA Glenn Research Center NEWSGROUPS: sci.optics Boris Broadside wrote: > I read about optical systems sometimes, but my sources are very patchy - > they are usually way over my head (e.g. Jane's Weapons Systems) or way too > basic (e.g. cyclopedias and dictionaries). > > What makes it a FLIR? I would think that a forward-looking infra-red > would just be an infra-red system that only sensed things ahead of the > carrying vehicle. But then, I see FLIR in 360 degree mounts sometimes, > and I never see anything called a "down-looking" or "side-looking" > infra-red. There must be some side-scanning thermal systems, right? > > Are FLIRs active, or passive? Or can they be both? > > Is thermal imaging a completely different thing than FLIR? Or is there > some overlap? > > What about those systems (like Snooperscopes and goggles) that aren't the > starlight/image-intensifier type. Do these count as FLIR and/or thermal > imagers? These goggles have IR illuminators, so I assume they are not > much good when used passively. Is it an "amplitude problem", i.e. they > are too crude to pick up background IR? Or is it a "frequency problem", > i.e. they are tuned only to their illuminator, which is presumably in a > different or narrower band than warm bodies and machinery? > > -- > Sincerely, > > The Reverend Boris Broadside > (not a real reverend) > > P.S. Please reply to the newsgroup Boris, FLIR is indeed simply an IR camera mounted on a gimbal. IR imaging is also sometimes referred to as 'thermal imaging' because the wavelengths imaged correspond to thermal energies, especially in the 8-12 um band for room-temp objects and the 3-5 um band for engine exhaust. Don't know about snooperscopes- never heard of 'em. Sometimes you have a near-IR illuminator like a diode, in which case you are seeing the reflection of an object (in near-IR) rather than thermal emission. Andy Resnick FROM: Patrick O'Donnell SUBJECT: Re: A very basic FLIR question DATE: Thu, 23 Sep 1999 11:57:30 -0700 NEWSGROUPS: sci.optics Andy Resnick wrote: > Boris Broadside wrote: > > > I read about optical systems sometimes, but my sources are very patchy - > > they are usually way over my head (e.g. Jane's Weapons Systems) or way too > > basic (e.g. cyclopedias and dictionaries). > > > > What makes it a FLIR? I would think that a forward-looking infra-red > > would just be an infra-red system that only sensed things ahead of the > > carrying vehicle. But then, I see FLIR in 360 degree mounts sometimes, > > and I never see anything called a "down-looking" or "side-looking" > > infra-red. There must be some side-scanning thermal systems, right? > > > > Are FLIRs active, or passive? Or can they be both? > > > > Is thermal imaging a completely different thing than FLIR? Or is there > > some overlap? > > > > What about those systems (like Snooperscopes and goggles) that aren't the > > starlight/image-intensifier type. Do these count as FLIR and/or thermal > > imagers? These goggles have IR illuminators, so I assume they are not > > much good when used passively. Is it an "amplitude problem", i.e. they > > are too crude to pick up background IR? Or is it a "frequency problem", > > i.e. they are tuned only to their illuminator, which is presumably in a > > different or narrower band than warm bodies and machinery? > > > > -- > > Sincerely, > > > > The Reverend Boris Broadside > > (not a real reverend) > > > > P.S. Please reply to the newsgroup > > Boris, > > FLIR is indeed simply an IR camera mounted on a gimbal. IR imaging is also > sometimes referred to as 'thermal imaging' because the wavelengths imaged > correspond to thermal energies, especially in the 8-12 um band for room-temp > objects and the 3-5 um band for engine exhaust. Don't know about > snooperscopes- never heard of 'em. Sometimes you have a near-IR illuminator > like a diode, in which case you are seeing the reflection of an object (in > near-IR) rather than thermal emission. > > Andy Resnick Gentlemen, I don't mean to antagonize, but the 3-5 um band passive sensors such as PtSi, microbolometers, et al make excellent imagery from room temperature objects. They also have better deltaT sensing than the 8-12 um sensors such as HgCdTe focal plane arrays. The 3-5 band has always gotten a bad rap because that's not where the maximum of room temperature blackbody photons occur. When considering 2D imagers, one must consider problems like spatial nonuniformity which can really cause big headaches for the 8-12 sensors. Sorry to spout off, this is a sore point from a previous life. Pat O'Donnell