Mapping Ground Zero with Lasers

securitas writes: "Amazing how the WTC disaster has shone a light on technology (pun intended). LIDAR (Light Detecting and Ranging) is the optical equivalent of RADAR. It's being used to create hyper-detailed maps of the WTC disaster site from an altitude of 5000 feet to detect shifts in the rubble as well as areas in danger of collapse."

Comments

LIDAR

[iota]

Just in case anyone is interested, LIDAR is actually what 'Laser radar guns' use to track your speed. So if someone ever tells you that they got pulled over because of a Laser gun, tell them it was LIDAR they should blame.

Try telling that to a cop... "No officer, its LIDAR! Really!"

jason

Re:how is this done?

[stjobe]

Quote the article:

"A week ago, with billows of gray smoke still pouring from the remnants of the World Trade Center, a twin-propeller plane flew 5,000 feet overhead, bouncing pulses of infrared laser light off the scarred terrain below."

So I guess they don't actually monitor it constantly.

Re:maybe offtopic

[budgenator]

not sure about any real attempt to dig it out, there's lots of problems there.
First the WTC was built in a "bathtub" because the foundation is below sea level so if the bathtub is cracked mud could rush in and de-stablize near by structures like subways, utility conduits and other building foundations. The WTC actualy re-inforced the tub internaly to prevent its colapse; now its rubble. To do this there is talk that they may have to drill through the tub and sink tie-backs into the bedrock or build cross-bracing beams and remove the rummble between the openings.
FYI Infrared lasers LIDAR is helpful here because of its excellent smoke-haze penetration and higher detail. Microwave side-looking radar might work but I think that the dust would either block or distorte the data. The sonar is probably used to probe the columns in near by buildings for hidden internal damage

Re:how is this done?

[mpe]

How do they monitor the site constatly from 5000 feet? is there a plane constantly circling around the site or is it done by a sort of balloon? can't this monitoring be achieved by satellites?

A satellite can't monitor such an area constantly, since Manhatten isn't on the equator.
The easiest way would be a teathered balloon.

Re:Interesting

[GospelHead821]

I'm not sure about the specifics, but if you pulse a very low-intensity sound wave through any substance, you can measure the distortion of the wave to see whether the material is behaving as you expect it to. If it is not, it is often because of miscroscopic structural defects.

LIDAR use before (VFX)

[malducin]

LIDAR technology is not soemthing new out of the blue. It has ben used quite a bit before. I saw it once at SIGGRAPH 99 (2 years ago). It's very useful for creating detailed 3D models. Kind of like a range finder, but it sweeps an area to get 3D range data out of it. It has even been used in films like in End of Days and What Dreams May Come. Here are a couple of articles from VFXPro.com

Panavision: Cinema in a New Light
Panavision's Panascan LIDAR System Integrates Cinematography

Interesting to see how this technology can be applied for a critical job. Especially when they start diging deeper below the level of the Hudson to detect any shifts.

CNN Map

[Alien54]

While not as neat or as detailed; this CNN map is interesting as an overview of the site.

http://www.cnn.com/SPECIALS/2001/trade.center/dama ge.map.html

Note that a High speed line would nice to have when viewing this

Google Search Stats for 9/11

[msheppard]

Zeitgeist type stuff for the 11th.