On September 11, 2001, Carol was working at a property adjacent to the World Trade Center towers and recorded the subject video shortly after the second airliner struck the South Tower. As part of her work assignment that day, Carol had a thermal imager with her that she used to record the short video that now appears on YouTube. To our knowledge, this video is the only thermal imagery that exists of the Towers prior to their subsequent collapse later that morning. More information regarding Carol's experience may be found in a paper that she authored in 2002. This paper may be accessed for free at our content-based website, Irinfo.org, here
As to your questions regarding temperature measurement, the imager was located too far away from the the towers to measure temperatures accurately. Additionally, emissivity and other camera inputs critical for accurate temperature measurement were not properly set at the time that the images were captured. Because of this, no temperature data should be inferred from the numbers displayed on the imager's monitor screen. To date, no one in our company has ever asserted that the temperature of the fires was below 120°C. However, it was still possible to produce thermal imagery even though the fire temperature was well above the temperature range displayed on the imager's monitor screen.
Undicisettembre: Could you clarify what you mean by
“though the fire temperature was well above the temperature range displayed”?
Thermal imagers that are capable of measuring temperature commonly have one or more fixed temperature measurement ranges. In order to measure temperature accurately, several factors must be addressed. Chief among these are that the temperature of the measured object must be within the chosen measurement range on the thermal imager. If an object's temperature is above the thermal imager's selected temperature range, it is possible for the thermal imager to produce an image; however, accurate temperature measurement is not possible. In such cases, areas which are above the selected temperature range are usually represented as the 'hottest color' on the imager display. The thermal images from September 11, 2001, were generated by a Flir Systems, Inc. ThermaCAM PM390. The temperature range was set to Range 2 (15° - 120°C) which allowed for imaging; however, would not permit accurate measurement of the temperature of the fire.
Undicisettembre: Is it possible that this thermogram is showing the temperatures of the smoke outside the building rather than the temperatures of the fires inside?
Although it looks very straightforward and simple, thermal imaging and accurate infrared temperature measurement are far more complicated than most people realize. While infrared energy behaves like daylight, there are several important differences that are not readily apparent to lay people.
First and foremost, thermal imagers cannot measure through most solid objects including glass and plastic that exceeding a few millimeters in thickness. Thermal imagers convert the normally invisible thermal patterns across the surface of an object into a color or monochrome image which is displayed on the monitor screen of the imager. Within a thermal image, the colors or gray shades represent the apparent thermal patterns across an object's surface. Thermal imagers that are capable of measuring temperature can also provide temperature values for imaged objects provided that the object is sufficiently close and the imager controls have been properly adjusted.
The thermal imager produced an image of thermal patterns across the surface of the buildings above and below the fires, in the breaches caused by the aircraft, falling debris, and in small part, of the smoke that was produced by the fires. What is of particular interest in the thermal images is that the smoke which is visually opaque is largely transparent to the thermal imager. The ability for thermal imagers to image through visually opaque smoke is why firefighters use thermal imaging to assist them in their firefighting efforts.
Undicisettembre: Had the thermal imaging camera been properly calibrated, would the displayed temperatures have been much higher than the ones in the video?
The imager was properly calibrated and functioning correctly on September 11; however, the imager controls were not adjusted to afford accurate temperature measurement of the buildings at the World Trade Center. Even if the imager controls were properly set, the buildings were too far away to accurately measure their temperature. Since the temperature of fire is in excess of 120°C, it is an absolute certainty that the fires were burning hotter than the chosen temperature range on the thermal imager.
Undicisettembre: Would it be possible to carry out post-processing of this thermogram?
While post processing of thermal imaging is routinely done, it requires that the images are recorded to 12 bit media using a PC card or the imager's internal memory. In the case of the video, this media is only 8 bit and accurate post processing is not possible.
Although many people have expressed opinions as to the significance of our thermal images, most are incorrect. The thermal images taken on September 11 show the thermal patterns across the Towers 1 and 2 and provide qualitative information regarding the upper portions of the buildings which were visually obscured by smoke. They do not provide any information regarding the temperature of the buildings nor were they intended to. They simply are a unique record that was captured as interesting images without any expectation of future analysis or scrutiny and without any belief that the Towers would soon collapse.
Undicisettembre: You said that the media is 8 bit. How come the text on the display says
“TIF file output = 12 bit”?
That is correct; however, the imagery provided by the thermal imager was recorded to 8mm videotape, which is 8 bit format. The video recording that appears online shows thermal imagery provided by the camera along with a scrolling data screen to the left of the thermal imagery that displays camera settings.
Undicisettembre: So the camera was set to 12-bit but the recording was on an 8-bit medium and therefore the data was reduced to 8-bit format?
The thermal imagery on the video is an accurate representation of what was recorded on September 11. There was no switching of data nor were the data post processed in any way. As described above, the thermal imagery that appears online is from an 8mm videotape that was used to record the output from the thermal imager. The videotape shows an exact representation of what was displayed on the thermal imager's monitor including thermal imagery and the dynamic on-screen data field described above.
Undicisettembre: This appears to be the original video shot by Carol Ciemiengo: the second part of the thermogram starts at 7:59. At 8:02 you can see the upper part of the tower, hit by the aircraft. Just below it you can see the lower part of the tower showing a higher than average thermographic temperature, although those floors were not involved in the impact and the resulting fire. What could have caused this?
This video was recorded by Carol Ciemiengo; however, the copy on YouTube was not uploaded by Carol or anyone working for my company. In fact, it was uploaded without our permission by someone who obtained a copy of the video that we provided to the National Institute for Standards Technology (NIST) in 2012. This copy was obtained under the US Freedom of Information Act (FOIA). Since we did not upload it to YouTube and were therefore not responsible for it, we have never commented publicly on it.
What you are seeing is thermal reflection from the fire in the South Tower on the surface of the North Tower. This reflection is due to the low emittance of the building's metal surface and appears well below the height of the area where the airliner impacted the North Tower. It is NOT another fire in the North Tower. For your reference, both towers are being imaged from the roof of a building located at Church and Vesey Streets providing a view of the North and East sides of both towers.
Undicisettembre: Let's talk about humidity, emission of infrared radiation and distance.
Due to the presence of carbon dioxide, moisture (humidity), and particulates, Earth's atmosphere will absorb or attenuate infrared radiation passing through it. Generally, this attenuation increases with distance since there will be more moisture and carbon dioxide at greater imaging distances. Even when atmospheric attenuation is relatively high, high temperature targets such as a building fire can still be seen due to the large amounts of heat that they emit.
Undicisettembre: So visible light travels better through air than infrared rays...
The wavelengths of visible light are, in fact, shorter than infrared...
Undicisettembre: ...and the greater the moisture in the air, the shorter the distance over which infrared rays are absorbed.
Undicisettembre: Just to clarify a point about moisture, on the ground the camera displayed a relative humidity of 50%.
Jim Seffrin: Your observation is correct. 50% is a default setting on the camera and it was not changed by the operator on September 11. On this model infrared camera, the setting for relative humidity only affects the accuracy of temperature measurements; it has no bearing on the thermal image. Because the relative humidity setting does not affect the thermal image, changing it to another value would not change the observed thermal patterns. Although temperature values appear in the data screen at the left, they are indicative of camera settings and not actual target temperatures. In fact, temperature measurement features were turned off during imaging on September 11.
Undicisettembre: Based on your experience, what are your thoughts about the events of September 11? What do you think about the various conspiracy theories about 9/11?
Jim Seffrin: While I cannot speak for opinions of others, I believe that the events of September 11 were a terrorist attack that was masterminded by Osama Bin Laden. The mass murder of 3000 souls was carried out by terrorists who flew the planes into the World Trade Center, the Pentagon, and a field in Pennsylvania. These incidents were not caused by the US government and statements that they were are simply outrageous claims by misinformed or misguided people.
Being an American, I fully respect that others may have opinions that differ from my own. I also respect critical thinking and the opportunity to ask questions as part of the learning process. Prior to forming an opinion, one has a responsibility to make certain that the information used to form opinions is correct. In the case of the September 11 attacks, there has been a wealth of misinformation and conjecture associated with the thermal imagery that appears on YouTube.
Since you first contacted me, I have spent a fair amount of time explaining the videos and answering your questions in the hope that others would benefit from accurate and truthful information. I can only hope that others consider the truth about the thermal imagery prior to forming an opinion. In light of this you are welcome to post my comments to your blog; however, it is unlikely that either Carol or I will respond to others on this topic as it is not easy to talk about and it can be a considerable distraction from our daily work.