From: Bruce Maccabee <brumac.nul> Date: Sun, 26 Aug 2012 14:19:05 -0400 (EDT) Archived: Mon, 27 Aug 2012 08:21:47 -0400 Subject: Re: Chasing Mexican UFOs >From: Michael Tarbell <mtarbell.nul> >To: post.nul >Date: Fri, 24 Aug 2012 13:39:53 -0600 >Subject: Re: Chasing Mexican UFOs >>From: Bruce Maccabee<brumac.nul> >>To: post.nul >>Date: Tue, 21 Aug 2012 21:59:34 -0400 (EDT) >>Subject: Re: Chasing Mexican UFOs <snip> >>As my article shows, the FLIR system was pointed toward the area >>of the oil field, about 100 miles away, as the plane flew >>eastward for many miles. I demonstrated reasonably good, >>although not perfect, agreement between the FLIR lights and the >>oil burnoff fires that were picked up by satellite that day. At >>the very least I was able to demonstrate that the oil fire >>explanation was plausible. The biggest question was, could the >>mid-IR (3-5 micron) radiation travel that far and be detected. I >>proposed to the Mexican Air Force an experiment using their FLIR >>equipped airplane to test the oil field hypothesis, but they > >never did it - or at least never told me they had. Their main >>argument against the fires was "we never saw them before or >>since." This of course, does not rule out the possibility that >>unusual atmospheric conditions occurred on the day of the >>sighting. >I know little about FLIR, but perhaps you can comment on whether this >first-order analysis, which doesn't much depend on the FLIR details, >holds any water: >Whatever the sensitivity of the FLIR may be (in terms of minimum >detectable wattage), we must consider whether IR radiation from >the atmosphere (essentially a ~300 deg-K black body) would swamp >whatever signal might be coming from the oil fields 100 mi. >away. >The mean spectral radiance of the atmosphere in the 3-5 micron >region is ~100 microwatts/sq.cm per steradian per micron of >wavelength [Ref.1]. So for an angular field of view of 3 degrees >(~.002 steradian), which is roughly the 'medium' field of view >setting for the FLIR in question, there will be ~0.4 >microwatts/sq.cm of 3-5 micron radiation being received from the >atmosphere alone. In order to be detectable, presumably the >target of interest must itself produce a non-negligible fraction >of this, let's say at least 4 nanowatts/sq.cm (i.e., 1% of the >background value). >Now consider the two principal mechanisms of radiant intensity >loss between the target and camera: geometric (1/R^2) >divergence, and atmospheric extinction (scattering and >absorption). >For geometric divergence: A spherically isotropic source in a >vacuum delivering 4 nanowatts/sq.cm from a range of 100 miles > would have a total radiant power output of (4 nanowatts) x (4pi >x [100mi x 1.61x10^5cm/mi]^2) or ~13 megawatts in the 3-5 micron >band. Let's say the earth's surface is a perfect reflector and >reduce that by a factor of 2, to ~6.5 megawatts. >For atmospheric extinction: The extinction coefficient in >maritime air in the 3-5 micron band varies considerably, but the >value at 4 microns is characteristic, with a value ~0.055/km >[Ref.2]. Applying this value across the entire wavelength band, >at 100 miles range the transmitted power is reduced by a factor >of EXP(.055/km x 100mi x 1.61km/mi), or roughly a factor of >7000.> >Hence the total 3-5 micron radiant power at 100 mi. range >required to noticeably exceed the atmospheric background >radiance at the camera is at least ~7000 x 6.5 megawatts or ~46 >gigawatts, which is some 7 times the hydroelectric power output >of the Grand Coulee Dam. >While it would clearly rule out the oil field flare theory, this >number is so enormous that I'm seriously doubting my own >calculation. Can you point out where/if I went astray? Not > really my area of expertise, so >please set me straight if necessary. > Wolfe L. W., & Zissis, J. G., The Infrared Handbook, Office >of Naval Research, Department of Navy, Washington, DC, 1978 > Yates, H. W., & Taylor, J. H., "Infrared Transmission of the >Atmosphere", U.S. Naval Research Laboratory, 08 Jun 1960 Thanks for your rather erudite comments. There are very few UFO sighting cases that can be discussed in such an analytical manner. You have correctly pointed out that the detection of an oil field burnoff fire 100+ miles away depends upon the path luminance and the attenuation as well as upon the power radiated in the FLIR bandwidth and the sensitivity of the FLIR. Radiation from the atmosphere is from a "wide angle" source whereas the radiation from an oil field fire is from a "point" source as shown below. The scale size of a fire might be on the order of 10 feet (e.g.: a cylinder 1 ft in diameter by 10 ft high) so the angular size of the longest dimension would be on the order of 10/(5280 x 100) = 1.9 x 10^-5 rad = 1.9E-5 rad or 1.1E-3 degrees. The Medium field of view (FOV) of the FLIR system is 3.4 x 2.6 deg. This FOV is spread over a focal plane array of pixels that is 320 by 240 (half the NTSC standard TV linear resolution). Thus one pixel in the MED resolution has an instantaneous (linear) FOV (IFOV)(vertical and horizontal) of about 3.4/320 = 0.011 deg. Thus the angular size of the fire, 1.1E-3 deg, is much smaller than the angular resolution of the sensor in the MED setting, 0.011 deg, so, to the FLIR system the image of a fire of that size and distance would "fit onto" a pixel. If the fire were very bright its light would "slop over" onto adjacent pixels, making a larger image than expected, because of optical aberrations, including light scattering and diffraction in the optical imaging system. Detection of a distant light requires a difference in brightness between the light hitting the pixel(s) which receives the light and the adjacent pixels that do not receive light directly (immediately adjacent pixels would receive light indirectly due to "sideways spread" because of lens aberrations and diffraction). In this case the electrical signal output of the pixel(s) which receive direct or indirect light must be greater than the output of the pixels that do not receive the light. Specifically, the output of the pixels that do not receive the fire light depends upon the path luminance (PL, light scattered in the atmosphere) that is received by the optical system within the IFOV of a pixel, while the output of the pixels that do receive the fire light is the sum of the fire light, FL, as attenuated by the atmosphere and captured by the aperture diameter of the receiving optics, plus the atmospheric path luminance within the IFOV: FL + PL. Thus the light from a fire "competes", not with the total path luminance over the whole FOV, 3.4 deg, but only that fraction that corresponds to the IFOV of a pixel, .011 deg or 1.9E-4 radians. The solid angle in steradians can be approximated as the square of this, or 3.7E-8 st. A more accurate result uses the equation B = 2(pi)(1-cos(A)) where B is the angle in st. and A is the half angle of the IFOV or 0.011 deg/2 = 0.00522 deg. Using a 10 digit calculator yields 2.6E-8 st. (The same calculation using 3 degrees as the total FOV is 2(pi)(1-cos(3/2)) = .0021 st, as you used.) This reduces your 0.4 microwatts of sky luminance over the whole FOV to the amount incident on a pixel, 0.4 x 2.6E-8/2.1E-3 = 5E-6 microwatts about a factor of 10E5 lower than you calculated for the whole FOV. A light source that is 1% of the sky luminance need only be 5E-8 microwatts (or 5E-14 watts). Using your estimate of the inverse square multiplication factor (100 mi written in cm and squared),3.2E15, we find that the needed output from a fire is on the order of 160 W without accounting for atmospheric attenuation. Your estimate of the attenuation factor probably does not include the slant path effect which decreases the attenuation but if we use your factor of 7000 then the fire must radiate 160x7000 = 1.1 MW in the wavelength band of interest. Whether this is reasonable or not I do not know, but at least it does not require seven times the output of the Grand Coulee dam. I would like to point out that, years ago, I would have attempted a "first principles" calculation of the amount of radiation received by the FLIR but no one could tell me the actual radiant power of one of the oil flares within the bandwidth of interest. And, of course, there were no data on atmospheric transmission for that day and time. Therefore I relied upon the measurements and calculations related to sighting line variation over time as the strongest evidence in favor of the fires. And then there are the lower faint lights below "the Twins" (the pair of brightest lights - see the article). Are these reflections in the ocean? Listen to 'Strange Days... Indeed' - The PodCast At: http://www.virtuallystrange.net/ufo/sdi/program/ These contents above are copyright of the author and UFO UpDates - Toronto. They may not be reproduced without the express permission of both parties and are intended for educational use only.
[ Next Message | This Day's Messages ]
This Month's Index |
UFO UpDates - Toronto - Operated by Errol Bruce-Knapp