This story revolves around the National Geodetic Survey (NGS), which is part of the National Ocean Service (NOS), which in turn is a part of the National Oceanic and Atmospheric Administration (NOAA), which in turn is part of the Department of Commerce (DOC). A wonderful example of government bureaucracy at its best. This is also about how specific technology will hopefully aid in the recovery of remains, as well as clearing and possibly rebuilding once that point is reached.
The National Geodetic Survey has a few main functions that it currently performs:
(Paraphrasing and direct quote from the "Who We Are" page.)
- Define and manage the National Spatial Reference System.
- Perform aerial photography surveys of airports within the U.S. and U.S. possessions to position obstructions and aids to air travel, with the end result being airport obstruction charts.
- Mapping the coastal U.S. and its possessions with the purpose of constructing navigational charts.
- "Developing standards and specifications for conducting geodetic surveys, coordinates the development and application of new surveying instrumentation and procedures, and conducts outreach activities including technical workshops conducted throughout the United States and an advisory program conducted with several states."
When I first heard that pilots from the NOAA Corps would be flying over the destroyed World Trade Center and taking photographs similar to the ones for use making airport obstruction charts, I wondered what the possible reason could be. This didn't seem to fit with the mission of NGS. I soon learned the purpose of these flights, and NOAA has recently shared them on the web in a press release.
NGS has been given the task of mapping the area to aid in recovery and cleanup. Using a special Kodak film that cuts down on smoke and haze, the pilots overflew and photographed the Trade Center wreckage on September 23rd and 26th at an altitude of 5,000 or 6,000 feet (about one mile), after previous work by NGS survey crews beginning on September 15th. Using the photographs and survey data taken, this data will be "used to provide a very accurate geographic network", to aid in finding where things are, such as support structures, elevator shafts, garage areas, and storage areas, so that recovery efforts can be concentrated in the correct locations. With the amount of destruction, there are very few points of reference, and I am told that, once the data has been processed, the locations of these specified areas will be plotted with accuracy to about one meter. In addition, determination of heights and depths into the ground will be sought so cleanup crews can know approximately how much debris must be removed, the size and position needed for the cranes, and whether they must beware of flooding from the surrounding waterways.
There is a fairly detailed summary on the NOAA news page showing what sort of technology was used to assist in the collection of the data. GPS was used to position ground and airborne mapping sensors, fixing lattitude, longtitude, and height within five centimeters. Two nearby Continuously Operating Reference Stations were also used for data collection. These provide continuous "carrier phase and code range measurements in support of 3-dimensional positioning activities throughout the United States and its territories." The aerial photographs were taken using a modified Cessna Citation aircraft.
The first result of the data collection was already completed at the time of the press release, and images from three different angles can be seen here, here, and here. The different colors represent heights, and the key can be seen on the NOAA news page. These images are known as LIDAR images, or Light Detection and Ranging. Basically, by measuring the round trip time of a laser pulse from the aircraft to the ground, it allows a fairly accurate elevation to be determined much more quickly than past methods.
The photos that were taken will undergo further processing, with the same software that is used for airport obstruction charts, called SOCET. With the use of high end workstation hardware, this software will be used to process digital photos using three dimensions for fairly precise measurements that may greatly aid recovery efforts. The largest image that had been on the web is much larger than the one linked to above and provides much better detail, but due to unforseen circumstances, the 14MB image is no longer available for viewing at the NOAA website. The images that will be used for processing will be many times larger, as a format other than jpg will be used to prevent data loss.
As the press release states, a similar flyover took place at the Pentagon. Needless to say, the Pentagon photos have not been made available to the public. It may be presumed that, since the recover of remains is a considerably smaller task at the Pentagon than the World Trade Center, the Pentagon may hope to use any data such as plotting where structural supports once stood to help the rebuilding effort take place as quickly as possible. This is purely conjecture, however.
Hopefully, the efforts of NGS, NOAA, NOAA Corps, and everybody else involved, will make the unenviable task of cleanup and recovery a little easier, and will help give some sort of peace to those that may never really know peace again -- those that are waiting for some sort of remains and ultimate confirmation that their loved ones are no longer with us. Obviously, those that are in the trenches deserve the credit, but this just seemed like one of those small stories that was worth sharing.