The view from between 1 and 7, approximately

OneWhiteEye:

It appears to me that the camera records the movement of the aircraft and we are ASSUMING the velocity is constant because the APPARENT rate of forward movement of a point on the aircraft is constant, BUT THIS IS NOT TRUE!!!!

Here's why:

Consider the case of a camera set up 50 meters from the wall looking precisely down the impact face. And let's say, for simplicity, that the aircraft is 50 meters long. Let's also say that the nose of the aircraft was moving at 872.75 meters per second at impact or 0.87275 meters in 1 millisecond.

This means that the nose of the aircraft apears to move through 1 degree of arc because tan 1 degree is 0.017455, hence the distance moved by the aircraft's nose is 50 x 0.017455 = 0.87275 meters

Now consider the motion of the tail at the same instant. It MUST move 0.87275 meters for a non-compressing aircraft, but this is a sweep of less than 1 degree of arc as seen by our camera. In fact, 1 degree of APPARENT motion of the tail is, if my trig is correct, about 1.7 meters of REAL motion of the tail. Or conversely, for a constant velocity aircraft, the tail should only move through about 0.5 degrees initially, and appear to accelerate to TWICE this angular speed by the time it impacts the wall. So, if the aircraft image APPEARS to maintain a constant angular sweep rate (which is, after all, what we are measuring with these smear-o-grams) the real aircraft is in fact decelerating ......

Thus, in this example, the "parallax error" is very large and cannot be ignored.

It looks like we need to know the distance of the camera from the aircraft to begin to deal with this problem!

Yes! Absolutely right, good math. The distance traveled in the field of view is an appreciable fraction of the distance to the camera unless this is zoomed. It's even worse when not perpendicular.


Maybe we can get scale from the tail target, a convenient invariant.

Edit:

I hope you can see this GIF animation, posted before. Watch the target grow in size over the frames until it stops with the red dot in the upper corner. Then, back to frame one, and the size reduction is visually obvious. Taking the size with boundary detection would be noisy, but reasonable accurate when averaged over several frames.

Give me a little time to finish the work on the program that will be used on the north tower antenna. It should work very well on getting the size of the checkerboard in each frame.

Isocontours... I think, says it all.


http://i6.tinypic.com/6ai760p.png

But the distance to the camera would be nice, too!

Another view of the checkerboard, tail, and sky. Inverted, filled, and looking from the lower right.


http://i7.tinypic.com/2whe2rk.png

Presumably that's why they included the handy-dandy scale bar on the Phantom II's fuselage.

Then Parallax doesn't matter.

Length: 62 feet 11 inches (19.1 meters)
Wingspan: 38 feet 11 inches (11.8 meters)
Height: 16 feet 5 inches (5 meters)

sub·son·ic
–adjective
1. noting or pertaining to a speed less than that of sound in air at the same height above sea level.
2. infrasonic.
http://dictionary.reference.com/search?q=subsonic

wcelliot:
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A point (of many) that goes straight over your head (because it's untrue), is that the acoustic spectrum of a 10microsecond spike goes all the way from DC to a MegaHertz, so it includes spectral energy in all bands, including the audio band (40-20,000Hz).
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1) a blast "spike" is not a sound wave, but you are still trying to conflate the two.
2) you repeatedly assert a 10µs duration of "spike" without substantiation.
3) Trippy's infrasound N-"spike" endured to the contrary for 2,050,000µs.
4) Arthur's "Typical HE pressure/time curve" for a blast endured to the contrary for 3,300µs
5) A 10µs "acoustic" (*cough*) "spike" that produced a wave of DC in the air would be quite fantastical and electrical, but it would not be acoustic.

With regard to point 5, I would try to retract gracefully to the effect that you were "only joking" or had inadvertently conflated sound propagation in the real world with the current produced in the output circuitry of an amplifier when driven to clipping, or something like that.


Of Trippy's wave you previously produced the following garble:
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The N-shaped waveform that Trippy provided showed a vertical leading edge, that sample is from the direct-path from the explosive. It would look like it had a slope less than 90degrees if it had been sampled at, say, 1million samples per second.
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This argument begins with a flawed observation about the angle mapped by the rise to maximum compression over a period of 0.67 seconds (670,000µs). The angle is actually a function of the resolution with which the time axis is viewed relative to amplitude. Zoom out to encompass longer durations on the map, and the rise and fall in amplitude will eventually be represented by a single pixel on the time axis, i.e. a "spike", eg:
___|___ = 30 minutes of time (horizontal axis) with a single 0.49Hz pulse in the middle at -20dB
That the leading edge of Trippy's spike is far from vertical is not due to a sampling rate that you don't know, or the inability to respond to faster pulses (or repeating cycles), but because it took 0.67 seconds to achieve maximum compression on a 14.67 pixels-per-second map.


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So I'm not saying that an explosive detonation is silent, I'm saying that you can hear it go off, but you can't hear anything distinctive between that and anything else that has a similar characteristics in the same audio band. It WILL have energy in the 20,000Hz to 1,000,000Hz part of the spectrum that you won't hear, though, and ordinary recording equipment won't capture.
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You were in fact suggesting that (1) detonation is silent, and that (2) all audible sound results from the original spike reverberating in the environment. After I mentioned that frequency in the world of sound doesn't shift as a consequence of distance propagated, you changed your story, suggesting instead that there is an audible component in the 10µs "spike" after all --- one that somehow endures at sustained amplitude for a significantly longer period. But like the reverberated frequency-shifted spike preceding it, this audible component can't include any "characteristic" qualities of an explosion -- because you say so.


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Any notion that explosives have a characteristic waveform would require the contributions of this part of that spectrum, and ordinary recorders simply undersample this part of the "characteristic waveform" and won't reproduce it. You can still hear the 40-20,000Hz part of the waveform, but that's less than 2% of the "characteristic spectrum" of the detonation.
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Any notion that explosives have a characteristic waveform would not require the contributions of an inaudible part of the spectrum. Notions don't require contributions from a spectrum. What you are trying to say, dogmatically ad nauseum, is that the only features distinguishing an actual explosion from any of your purely hypothetical explosion-like alternatives must be found outside the discriminable region. But this is just an ad hoc assertion, poorly framed by you to exclude perfectly sound evidence for the use of explosives.

Incidentally, the human frequency spectrum technically begins at 20Hz. Your lower boundary, at 40Hz, is a full octave higher.


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But, let's consider that part for a second - the spectrum of a real explosion goes all the way up to MHz frequencies, ...
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Three problems in just half a sentence:
1) We aren't analyzing the inaudible domain
2) You have not substantiated your repeated MHz assertion
3) You are still conflating a shock wave with sound waves

Thus, let's not consider that part of the spectrum.

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20kHz is only 2% of the way up in frequency, but all those sonograms you provided seemed to peak-out at 10-11kHz. What happened to the 10-20kHz components?
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1) 2% of your personal assertion doesn't weigh much on the scales of evidence.
2) I didn't post any "sonograms" - I posted a spectral distribution extracted by Fourier Transform.
3) High frequencies attenuate with distance propogated at a much faster rate than do low frequencies - perhaps you have heard?
4) Audio compression codecs discard a lot of information that we tend to ignore. Lower sampling rates used for distribution online tend to also lower the frequency response. Gosh! -- I thought already you knew that!
5) After heavy compression and resampling at a meagre 6kHz, I can still clearly and easily discriminate between Ella Fitzgerald and Billy Holiday---but not by inspecting a visual map of amplitude over time, or a visual map of spectral distribution over time. So how do I do it?
6) I can clearly and easily discriminate between brass and wind and strings and drums and chimes and explosions and glass breaking and birds twittering and 1812 overture canons --all at a meagre and very dull 6000 samples per second. Given the high-amplitude of high frequency components not encoded at this rate, how do you think I achieve this miracle of pattern re-cognition?

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See, with your expensive speakers,
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Did I say that my speakers were "expensive" at some point?
As it happens, I was employed for several years as a professional audio specialist for a multinational corporation that produces sound engineering bibles, domestic hifi systems, professional audio recording equipment, professional mixing equipment, concert amplification, sound reinforcement systems, signal processors, drums, guitars, trumpets, pianos, flutes, digital synthesizers, and a vast array of other indistinguishable noise producing things like that ---- so the contrary is quite true.

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the top-end frequency response is limited by the mass of the speaker cone and the power of the speaker coil - the coil's force has to accelerate the speaker-cone mass to reproduce the high slew-rates associated with high-frequency sounds. Sound familiar?
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Remember how I already explained to you that my speaker diaphragms could easily be made to oscillate at rather high frequencies due to their relatively low mass?

Does my demeaning tone sound familiar?


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That's why the expensive speakers brag about their power and the REALLY expensive speakers brag about what their speaker cones are made of - low mass/high-rigidity materials.
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1) Expensive hifi speakers don't brag about anything. Marketing people do.
2) Marketing people brag about the engineered capacity of speakers to adequately handle high power levels from amplifiers, but the reasoning has nothing to do with the power required to produce high frequencies - au contraire!
3) Battery-powered devices produce high frequencies at high amplitudes for hours at a time at very low cost, and with little engineering effort (consider the domestic battery-powered smoke alarm) -- but you never see a battery-powered subwoofer.
This is because low frequency cones are necessarily designed with a large surface area in contact with a large volume of air, and because they have a substantially longer excursion range than tweeter diaphragms. Although not forced to oscillate at the rapid rates required of a tweeter, they must impact with a significantly larger volume of air during each excursion. Human perception of the spectrum is not linear over the volume range, with high and low frequency perception declining at lower amplitudes (the reason most amplifiers have a compensating loudness switch or contour). Thus, to produce high fidelity sound that appears balanced over the spectrum at even moderate volume requires a generous supply of power --- most of it to drive the bass. Additionally, high power output is equated with lower distortion at all volumes, higher damping factor resulting in a tighter bass response from passive cones at all volumes, and a higher signal to noise ratio at all volumes.

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But as you've pointed out, concrete floors, even ones 600x bigger across than they are thick (like a playing card) are still concrete, and that's fairly massive. Then again, the structural steel connected to that concrete was stressed to the breaking point, so the energy available to move that concrete was a lot greater than you speakers' voice-coils.
The point is, that a sudden release of mechanical energy coupled to a big floor will make a pretty good approximation of a woofer reproducing an explosion.
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It will take not just a lot of energy, but a special kind of miracle to make the steel-reinforced concrete woofers oscillate repeatedly at a rapid rate while they pancake(!), piston(!) and powderize(!).
That is why you can't reference a real world sound similar to the recorded explosion on 911, but I can.

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It'll have some upper limit to its frequency response,
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This acoustically rational statement is startling and almost shocking in the midst of so many unsound claims. Yes - that is true.

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so the top-end of its frequency spectrum will tend to drop off. I wouldn't expect it to go as high as 20,000Hz, would you?
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No - I would not expect a steel-reinforced concrete floor of any dimension to oscillate or resonate at 20,000 cycles per second if struck.

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But a block of C-4 definitely WOULD have higher-frequency components all the way up to the MHz.
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If you struck a block of C4 with a drumstick, I don't think it would oscillate with discernible amplitude at any frequency for significant duration. If you want to detonate the C4, then a very different kind of explanation is required to account for the resulting sound.
You don't seem to comprehend this requirement.

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So show us a sonogram from a WTC collapse that has spectral components in the 10kHz to 20kHz range and let's talk.
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Learn how to reference your dogmatic assertions, then maybe we can talk like adults in a scientific manner. This would preclude use of the term "sonogram," but would include uncompressed sound extracted from Naudet footage extending from approximately 14Hz to 18kHz --- more than sufficient spectrum.

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Oh, and find me a microphone that has a DC response. Without the DC component, the waveform captured MUST be balanced at zero, so that high-pressure shock wave has to go negative to balance-out the response. Otherwise, it'd be capable of detecting barometric pressure. You want to impress me, grab a book on Fourier Series and read a few chapters, you'll learn a lot about more about acoustics than you currently do.
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Show me just one of these amazing sounds you speak of that propagate as direct current.
Then show me DARPA's request for development of a microphone for recording explosions.

But first you must substantiate the 10 microsecond duration for your non-acoustic pulse.

Cheers.

Arthur::
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Except Al, what he means by "With the USE OF DELAYS ... We can control sound levels" is EXACTLY the reason you get the BANG BANG BANG BANG associated with HE demolition.
Consider the ALTERNATIVE.
No Delay Then ONE MUCH BIGGER BANG.
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What is the maximum amplitude threshold of human hearing in decibels?
What is the relationship between distance of propagation and amplitude?
Suppose I line up 120 linear shaped explosions in rapid sequence on my digital multitrack and superimpose (mix) the 120 individual waveforms.
What do you suppose the resulting waveform will sound like?

Also, what do you suppose a linear thermite or thermate cutter might sound like?


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Which of course, as the sound tracks from multiple sites have shown, the collapse begins with the slow pulling in of an exterior wall and when the motion becomes obvious its well BEFORE any EXPULSIONS of high speed debris or before any loud sounds are generated by the falling structure.
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As a matter of documented fact, at least one expulsion occurred at 9:37AM - well before the motion became obvious.

Do you think a notable sound associated with the ejection might have been captured on the plaza video?

If a linear-shaped charge or a kicker charge was detonated in the core near the 77th floor, how much attenuation would you expect the building to impart on the amplitude of the resulting sound before it reached the perimeter and propagated approximately 1000ft to the plaza below?

If an ordinary magnitude linear-shaped charge or a kicker charge was detonated in the core near the 77th floor, do you think someone at the plaza would hear an explosion from the basement below almost instantly, followed by an explosion from above almost a second later? --- or would they hear just one explosion from above? -- or, being at street level with a relatively high noise floor from traffic, would they be more likely to hear nothing of significance?

If high-speed explosives were employed in conjunction with thermite-cutters of some kind, would you expect acoustic evidence recorded at street-level to be more evident during the last moments of collapse, or the first?


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As to your comparator, BFD.
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?
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One is a shaped charge set off in the open, the other is an UNKNOWN sound from an UNKNOWN source at an UNKNOWN distance.
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The sound produced by "something unknown" on 9/11 was similar enough to the shaped charge explosion that it would pass as a substitute for "the real thing."
It did not resemble the sound of a car crash, an aircraft wing snapping, a train coming off the rails, a drum, "something heavy falling on the floor from above," or a "catastrophic brittle failure."


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Al, you get more desperate with each passing post
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Your gross misrepresentations get more inflammatory and bellicose by the day. eg:

QUOTE

The video shot from the WTC plaza captured an intriguing event at 9:37:04 a.m. A jet of air, dust, and a large piece of debris was ejected from a window, 77-355, on the 77th floor at an extremely high velocity. Longer distance videos show that puffs of smoke and/or dust appeared simultaneously on the east face from several open windows near the center of the 78th floor and from open windows on the north side of the 79th floor. Interestingly, the smoke flow from the windows on the west sides of the 79th and 80th floors, which had decreased markedly by this time, did not increase. Within 14s of this release, a large fire either grew or became visible near the center of the east face on the 82nd floor. [b]A long distance video shot from the south showed that fire and smoke were pushed from multiple locations on the south face at the same time the strong jet occurred on the 77th floor of the east face. -NIST NCSTAR 1-5A, WTC Investigation (p. 346)