GA.CJJ@Forsythe.Stanford.EDU (Clifford Johnson) (12/22/89)
From: "Clifford Johnson" <GA.CJJ@Forsythe.Stanford.EDU> } > there is a large IR signature associated with heat } Thermal radiation is emitted over a broad range of wavelengths . . . } capabilities depend, of course, on the sensors, the targets of } interest, and the background against which those targets are observed. While not an expert, I believe the distance of the sensor from the source is also important, especially because the atmosphere absorbs radiation except at certain wavelengths. Thus, viewed from space, an oil fire has the same infra-red radiation pattern as a missile exhaust plume. Given this look-alike phenomenum, the term "signature" is very misleading. Are satellite sensors sufficiently sensitive to detect residual differences in spectroscopic distributions as to reliably differentiate between various hot sources? I don't believe so. Can anyone enlighten me? To: MILITARY@ATT.ATT.COM
patterso@ads.com (Tim J. Patterson) (12/23/89)
From: patterso@ads.com (Tim J. Patterson) In article <12535@cbnews.ATT.COM> GA.CJJ@Forsythe.Stanford.EDU (Clifford Johnson) writes: >Are satellite sensors sufficiently sensitive to detect residual >differences in spectroscopic distributions as to reliably >differentiate between various hot sources? I don't believe so. >Can anyone enlighten me? There is indeed a spectroscopic difference between an oil fire and a missile plume. In order to detect a spectroscopic difference you need a multi-channel IR sensor-aka multispectral. Certainly neither of the 2 available multispectral satellites (LANDSAT TM, and SPOT) has the IR resolution to see the spectral difference. While it is theoretically possible to do this, optical and detector plane technology in the IR region is more difficult than much of the visible region so probably this type of discrimination will have to continue to be done using target/background discrimination and spatial cues.
nadel@aerospace.aero.org (Miriam H. Nadel) (12/23/89)
From: nadel@aerospace.aero.org (Miriam H. Nadel) In article <12535@cbnews.ATT.COM> GA.CJJ@Forsythe.Stanford.EDU (Clifford Johnson) writes: > >While not an expert, I believe the distance of the sensor from the >source is also important, especially because the atmosphere absorbs >radiation except at certain wavelengths. Thus, viewed >from space, an oil fire has the same infra-red radiation pattern >as a missile exhaust plume. Given this look-alike phenomenum, >the term "signature" is very misleading. > The atmosphere is more important as a source of refraction. The observed position of an IR source depends, in part, on how much atmosphere you're looking through. >Are satellite sensors sufficiently sensitive to detect residual >differences in spectroscopic distributions as to reliably >differentiate between various hot sources? I don't believe so. >Can anyone enlighten me? Generally satellite sensors are relatively broad band. Differentiation between various IR sources has more to do with their pattern of motion than with their spectroscopic distribution. To use your example, an oil fire will be in a fixed location with respect to the earth, while a missile exhaust plume will have a characteristic motion, depending on the type of missile. One can detect relatively small changes in position, depending on the exact configuration of the sensor focal plane. It isn't unusual to have several hundred separate sensor cells. By the way, the biggest source of noise is probably IR radiation from stars. A common approach is to use a catalog of known star positions to remove them from the data stream. This has more to do with reducing processing load than with the possibility of false detections, however. Miriam Nadel -- One of the 60% of Americans who do not spend a lot of time on their personal appearance. nadel@aerospace.aero.org
wanttaja@beaver.cs.washington.edu (Ronald J Wanttaja) (12/23/89)
From: ssc-vax!wanttaja@beaver.cs.washington.edu (Ronald J Wanttaja) > While not an expert, I believe the distance of the sensor from the > source is also important, especially because the atmosphere absorbs > radiation except at certain wavelengths. Thus, viewed > from space, an oil fire has the same infra-red radiation pattern > as a missile exhaust plume. Given this look-alike phenomenum, > the term "signature" is very misleading. > > Are satellite sensors sufficiently sensitive to detect residual > differences in spectroscopic distributions as to reliably > differentiate between various hot sources? I don't believe so. > Can anyone enlighten me? Stationary sources don't cause much problem. Oil well fires differ from missile plumes in two important categories: They don't move, and they don't vary significantly within short periods of time. Missiles don't just turn on and off; there is a distinctive time-intensity history for each than can be used to determine missile type. Motion is also important, of course, since oil wells don't generally move. Missiles accelerate. So, normally there's little problem telling an oil well fire from missile launches. However, in weird cases, the software can be fooled... that's why there are men (and women) in the loop. However, as for telling a stationary tank from a bakery, a satellite would be in sad shape, for the reasons you mentioned. Ron Wanttaja (ssc-vax!wanttaja)