Why do not we see clearly an airplane in footage of the Pentagon?

This question I'm often made by those who approach for the first time to the analysis of the attack on the Pentagon on 11 September 2001.

I will try to give an answer. In the book "Debunking Myths 911" , in Chapter 3, it is addressed the subject of surveillance cameras in the Pentagon and the analysis of the question movies released by the DoD (Department of Defense) following the conclusion of the Moussaoui trial. .

These movies, since their release, were the subject of many criticisms and analysis, because in fact the general public expectation of seeing a plane crash into the Pentagon, similar to what is seen in many movies taken from different angles the impact of the Boeing 767 against the South Tower, has been disappointed.

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In the movie you see a widespread impact, followed by an explosion and subsequent development of a huge cloud of flames, but a plane, as would be expected commonly to see him, not even a shadow. But are we really sure that you had to see a plane? That is, we would really have expected to see an airplane going to slam into the Pentagon, flying at very low altitude until final impact?

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In the book of Popular Mechanics appear these phrases:

"A Pentagon spokesperson tells Popular Mechanics That the video was taken with a Philips LTC 1261 security camera and recorded at one frame per second. Jerry Housenga is a technical product specialist with Bosch Security Systems, Which bought the Philips room division in 2002. According to Housenga, it was unrealistic to think That the low-quality security camera footage would reveal the crystal-clear image of a Boeing 757 traveling at 780 feet per second. While most advanced security and surveillance cameras can be in September to capture real-time video, the attached recording systems are almost always at September Significantly slower frame rates in order to conserve storage space. As a result, it is unlikely That the recording system of any nearby security camera would be in September at a rate high enough to capture the speeding plane with decent resolution. "

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The airplane then, according to Popular Mechanics, flying at a speed of about 780 feet / second, that is, equal to 237.9 meters / second, that is, to give the sense of the magnitudes of which we are speaking, with a speed of 858 kilometers / Now. The surveillance cameras at the Pentagon that made ​​shooting was under NTSC standard, then produced 29.97 frames per second in 60i mode, that is, by capturing 60 fields per second. Each frame (frame) consists of two half-frames or field. Until proven otherwise, it is also reported publicly so far, it would then interlaced analog cameras operating in NTSC standard, at a fixed location.

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Regarding the analyzes that follow, I would like to clarify that I have consulted over time a large amount of technical and talked with technical operators sources who work for years in the field of audio-video production, both of CCTV specialists video production / broadcasting, but I however, specifically anyone to not trust my evaluations and to make their own checks on what I say below, by screening all my doubts. Referring instead to a widespread source of surfers on the net, like Wikipedia for readers' convenience, we read:

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"The NTSC format is interlaced , where 60 semiquadr the form 30 frames per second (in fact the exact frequency is of 29.97 per second - 60 Hz ). Its resolution is 640x480 pixels "

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But to understand the meaning of the phrase, you must understand what interlacing, again from Wikipedia :

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"Interlacing (or interlace) is a technique for improving image quality in a video transmission, which limits the extra consumption of bandwidth. It consists in alternating display between the lines of a frame. Viewing the entire frame and then passing to the next, with cathode ray tubes was created an unfortunate side effect: Because the electron beam is drawing the image on the tube to get started from the bottom, the top of the screen was more stable to the human eye, while the lower part was perceived as in constant vibration (given that remained visible for less time). Interlacing allowed to avoid this. The technique is to draw on the screen the odd lines and then the even lines (PAL / SECAM) or vice versa (NTSC). In this way, the retina of the eye of the viewer is immediately affected by the entire frame, which is then (1 / 50th of a second for PAL, 1 / 60th for NTSC) affected by the remaining rows (sic, Ed). RCA was discovered by engineer Randall C. Ballard in the late '20s. It has been used for TVs from the beginning of the 70s. Side effect of enhancement is the effect flicker (flicker) that, at times, makes the unpleasant vision. Today, with the birth of the first cathode-ray tubes that worked at 100 Hz (PAL) and subsequently with the use of plasma and LCD technologies, and with the emergence of high definition formats, it is no longer necessary to transmit the image in interlaced format. It is important to understand that the interlacing is a television technique and not cinematic. A film is necessarily made ​​of frames "full" and even if broadcast on television will have no interlacing (ie the odd lines and will equal about the same time) (see note 1, ed) . Today it is considered a special effect the option of de-interlacing, that is, the interlacing removing and creating (artificial) of a full-frame information. "

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Note 1: in order to clarify what is stated Wikipedia, which may be a little 'difficult, it is necessary to explain that the passage of the films in electronic format is done with a special selective technique, for which every single frame of the film is taken up twice, so that taking the next field of the frame pairs, these are always referred to the same frame of film. A further problem, which often flies over, is that on the film format works at 24 frames / second, while the video format works at 25 frames / second (PAL) or 30 frames / second (NTSC), for which, in the absence of suitable corrections, the original length of the film varies depending on the video format chosen, with the shorter video format than on film.

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From which it is understood that, put in a nutshell, the human eye is tricked by the rapid succession of 60 fields per second, drawing the synthesis of moving images.

. At this point we just have to figure out what a half-frame, or field, and we always rescues Wikipedia , in English:

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"Other technical standards in the final recommendation were a frame rate (image rate) of 30 frames per second Consisting of two interlaced fields per frame (2: 1 interlacing) at 262½ lines per field or 60 fields per second along with an aspect ratio of 4: 3, and frequency modulation for the signal sound "

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and yet :

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"With progressive scan , an image is captured, Transmitted and displayed in a path similar to text on a page: line by line, from top to bottom. The interlaced scan pattern in a CRT ( cathode ray tube ) display completes such a scan too, but only for every second line. This is the carried out from the top left corner to the bottom right corner of a CRT display. This process is repeated again, only this time starting at the second row, in order to fill gaps in Particular Those left behind while performing the first progressive scan on alternating rows only. Such scan of every second line is called a field. The afterglow of the phosphor of CRT tubes, in combination with the persistence of vision results in two fields being perceived as a continuous image Which Allows the viewing of full horizontal detail with half the bandwidth Which would be required for a full progressive scan while Maintaining the Necessary CRT refresh rate to prevent flicker.

Only CRTs can display interlaced video directly - other display technologies require some form of deinterlacing . "

. So it is understood that the field is no more than the image taken in alternate rows to which each frame consists of two fields, each of which shows only the even rows or odd, in a manner that the persistence of the image in retina or the CRT does replenish the impression of a full frame.

In summary, the footage of the Pentagon would have been taken by cameras working in interlaced mode at 60 Hz, that is, with the recovery of 60 fields per second for a total of 29.97 frames per second. That said, it would be incorrect conceptual comparison of a camera with a film camera, because with the same shutter speed (1/60 second), the camera captures the image on film ALL while the analog camera that works interlaced mode, capturing only made a field, that is, or even lines or odd lines of the frame, but not both. This stems from the electronics that controls the operation of the camera. The problem that arises, then you understand what would be expected from the vision of a player of a video taken from an analog camera in a fixed location, an object in rapid motion which crosses the shooting range, shot and saved on videotape with time lapse recording 1 frame / second and converted to mpeg1.

. The problem is complex, because it is necessary to distinguish the various steps:

1. interlaced analog camera at a fixed location that resumes;
2. time-lapse system that records on videotape (in the article we consider a digital recording system, as a safety case; if the system was analog, the quality of the recorded and reproduced would be even lower);
3. any export of other support movie, for example CD-ROMs or DVDs;
4. reproduction of digital movie on a player.

The combination of the first three items listed determines the quality of digital video distributed on CD-ROM or DVD, while the fourth determines the quality of the perception of that digital movie by the end viewer.

. WHAT THE CAMERA resume?

. We begin to observe then what would resume the interlaced analog camera at a fixed location. The surveillance cameras at the Pentagon that would resume the famous movies of the impact would be, unless new documents are not currently known and it is also reported at the time, analog interlaced NTSC, Color, the automatic iris pattern, with a shutter speed of 1/60 second. The camera cuts to a fixed scene, background objects and properties, and objects that move within it (machines, people, clouds, etc.), and captures the field shutter speed of 1/60 second.

We construct a simplified model to understand how it behaves airplane flight AA77. The air penetrates in the visual field with the speed, estimated, to simplify the model and not weigh it down with unnecessary formulas, equal to that of impact, of about 237.9 m / s, according to a trajectory that, in the first approximation, we can consider have an angle of approximately 46 ° with the straight line joining the airplane with the camera. In this simplified case, the aircraft's speed, point to point of the linear trajectory described by the airplane, can be decomposed into the two radial and tangential components with respect to the center of a hypothetical circumference with center in the camera and passing through the instantaneous position of 'airplane.

The tangential component of the airplane's speed is one that tells us how much you sposterebbbe the airplane for each second of a theoretical line "quasi-parallel" to the CCD plane which incorporates, while the speed of the radial component tells us than you come close, specifically, the plane of the camera.

Put simply, the tangential component tells us to what would move the second the airplane at a constant distance from the camera, while the radial component tells us how fast the plane would approach or moves away from the camera. The first would be responsible of detections of linear movements of the camera on the CCD, the second of changes in dimension of the object taken.

So we have, in sum, an object that would move in its representation on the CCD and that, simultaneously, would approach changing its size and the shape of the projection. Simplified assumption of initial angle of 46 °, for EVERY FIELD, that is, every sixtieth of a second, the object would move from the point considered linearly, in parallel to the CCD, of 2.85 me would approach of 2.75 m. That is, the single frame of 30 per second, is composed of odd and even line that relate to the same object that has been moved in its projection on the straight line parallel to the 2,85 CCD me that approached to 2.75 m . This reasoning extremely simplified, only applies to the initial point of the actual trajectory, because for each point of the same vary both the distance from the camera that the angle at which it breaks down the speed vector, and then vary accordingly the variations of the displacements and perceived dimensions and recorded by the CCD. It 'is therefore clear that it is unthinkable to compare a complete image taken at 1/60 second from a film camera with an interlaced frame captured from an interlaced analog camera, in which the odd and even lines of the same frame shooting the same object actually placed differently in space. This is because the even rows and odd rows of the same frame actually originate from field tripped at a distance of 1/60 of a second.

As the airplane approaches the impact with the Pentagon, if we admit, for a model of simplicity, the constant airplane speed (but it is a reductive hypothesis, because in reality the airplane is being accelerated physics), decrease however, the radial component of the velocity increase and consequently the tangential (to the rule of the parallelogram of carriers composition, according to the new radial and tangential directions of concentric circles with the center in the camera and passing through the point at which is located the plane) .

Then the plane, only to geometric and non-physical issues, would undergo an acceleration tangential and radial deceleration compared to the camera, that would decrease the magnification of the object perceived by the CCD, but would increase the difference between the spatial positions projected on the parallel to CCD between the odd and even lines of the same frame.The effect, out of the model would be further amplified by real airplane acceleration. This already makes it clear that it is difficult to expect to see a well-defined plane as the fictional town might think.

It then raises another question: what would capture the CCD if the sixtieth second when remains "open" the shutter the light that strikes the CCD only comes in part from the object and partly from the bottom remains intact?

Let me explain: if at a certain instant the shutter is opened to capture a field (for example the even rows of the frame) and we considered, again for example, a point of the shooting range that he was 2.50 meters before the tip aircraft, airplane that moved with tangential speed of 171.1 m / s, this time taken would remain for most of the exposure time when the light of the hard landscape, and only while the shutter is about to close would be reached by airplane tip (which, remember, would move in the sense of 2.85 m) ring road.

What would record, then, the CCD?

The background with a haze due to the airplane that Came To almost closing shutter? Probably yes; we would have the same effect for a point that was in the airplane tail, in which the opening shutter we would for a brief moment the airplane tail, but then, for most of the exposure period, the background fixed.

So in summary, we would have dynamic effects related to the geometry of the airplane actual trajectory and fixed camera shooting point, dynamic effects due to the airplane agents physical forces and effects "Video Electronics" related to the operation mode and the camera shooting . .

WHAT would register THE VIDEO RECORDER?

. The acquisition system, as mentioned, records images from the camera, but to allow adequate time autonomy, not recording all NTSC 29.97 frames per second (each consisting of 2 field), but records 1 frame for every second, according to a saying time-lapse recording system.

Which frame among 30 frames per second?

It depends on how the system is set, but certainly, at each end of the second, is entered in the corresponding frame.

Know how it set the recorder is still important, because the 29.97 frames per second are very different to each other "content" of the image.

How likely are you to record just that frame in which the plane is full, if it exists at such a frame and with all the doubts of the previous point?

The selective skimming due to the time-lapse recording is such that the airplane, although shot by the camera, may not be registered, because it is part of those frames that would not be considered by the recorder.

A further information that you should have certainty before advancing hypothesis is the presence or not of an apparatus for de-interlacing of the input before registration and any other signal circuitry that could alter the structure of recorded field compared to those caught by camera.

. WHAT WOULD BE EXPORTED ON CD-ROM or DVD?

. Another problem would arise then from the subsequent export of the stored frame from the video cassette recorder on CD-ROM or DVD.

Given that the recorder is recording 1 frame per second from the camera, if it were reproduced in the recorded movie (or rather the series of recorded images) to the normal speed of 29.97 frames per second, we would have an acceleration effect of 30 times, for which the movies should be exported have been obtained by techniques which are permitted by the normal CCTV digital players with which you can fix at will the playback speed, or, another cruder technique would be to replicate 30 times each frame before producing export movie.

The movie recorded in NTSC standard has a single frame of the definition of at least 640 * 480 pixels votes, but the movie is diffused by the DoD to MPEG1 format, which has a single frame resolution of 352 * 240 pixels, that is by far lower than the native format recorded, admitted that this was right in the NTSC standard.

So in addition to all the above factors, in the export process one has, to force things, a further reduction of image resolution, in addition to a compression that uses a lossy format, which may, compared to the original, introduce a further complication in the individual pixels of representation.

It would therefore be necessary to know which treatments would be subjected the movie recorded on videotape before exporting it to MPEG1, for example, may have been de-interlaced.

A brutal form of de-interlacing, and compression is to eliminate completely a field, leaving only or the even rows or odd ... Something surely must have occurred, given that the number of lines of distributed MPEG1 movie is half the size native NTSC.

. SHOWS WHAT A PLAYER?

. It 'clear that the quality of the player (hardware and software), affects the usability and the final level of the MPEG1 movie compared to the end viewer. A bill would see a video-CD, that is, an MPEG1 movie, on a player from room, another play a MPEG1 file into a professional video editing program on your computer. But these doubts are not based on technical considerations related to movies in itself, although, no doubt, several players provide quality various playback of the same digital file.

. CONCLUSIONS

. In light of these simple considerations, my answer to the question "why do not we see clearly the Pentagon plane in the films released by the DoD?" Is that not knowing:

• what level of detail of the original images on videotape,
• how it made the acquisition chain, processing and storage of frames (including the setting of the equipment),
• such treatment has undergone the first footage of the MPEG1 compression

it is not possible to establish a reliable degree of certainty what the copy in MPEG1 format is roughly equivalent to the original recorded video content: the only sure thing for me is that the videos released by the DoD are definitely inferior by definition and by quality than the original, and technical doubts outlined above do not help in order to have certainty from which to proceed.

In light of the above, I consider that it would be statistically more suspect a movie that showed clearly a plane striking the Pentagon: the movies released by the DoD, following a FOIA request after the close of the Moussaoui trial, are not for me a try conclusive of the presence or not of a plane at the Pentagon, but if I had no option, the clues are more in favor of the presence of a plane of his absence.