If an act of terrorism were to occur again in the New York City region, the Global Positioning System (GPS) base station, located at New Jersey Institute of Technology (NJIT) would go into immediate action. The system, which was used extensively by rescuers during the World Trade center recovery effort, provides very high accuracy positioning, says Joshua Greenfeld, Ph.D., professor of civil and environmental engineering at NJIT.
Greenfeld manages the GPS at NJIT. The system enables viewers to monitor and map a targeted region using almost invisible equipment. The military coalition led by the United States outside of Iraq is using GPS to direct manpower, move equipment and navigate vehicles, warplanes, tanks and missiles.
To the naked eye, a GPS is the essence of “smart” technology. At a base station, such as the one at NJIT, a viewer sees no more than a small antenna, which is no larger than a common rooftop apparatus to improve television reception. Inside the building, computers display information relayed to them from the antenna.
The workhorses in the process are, of course, GPS satellites, positioned about 13,000 miles above earth. The satellites broadcast electro-magnetic signals that are received by special equipment. The electro-magnetic signal is used to measure the distance between the GPS receiver and the GPS satellites. Distances measured from at least four satellites determine the position of the GPS receiver. The equipment ranges from a small hand-held device, the receiver, which is capable of positioning with an accuracy of plus and minus 30 feet, to a device that is small enough to be carried in a backpack. The diminuative latter, if used in conjunction with a GPS base stations, can deliver an amazingly correct position that is less than an inch from where it is really located.
NJIT houses one of the nation’s most accurate GPS base stations. It is a member of an international network of GPS base stations that collects and processes GPS signals every second on a 24/7/365 basis. The network is called the Continuously Operating Reference Stations (CORS). At the NJIT base station, the accuracy of the position has been refined to one tenth of an inch. Other high-end receivers can use this base station accuracy to position themselves within a fraction of an inch in real-time.
During the world trade center disaster, NJIT’s GPS system worked something like this. Low flying specially equipped airplanes hovering above Ground Zero took three-dimensional digital aerial and composite images created from thermal and other sensors of the rescue effort. The base station at NJIT computed the correct position of the airplane and its sensors. Consequently, highly detailed, accurate three-dimensional maps and spatial information databases were created from these flying missions. The National Oceanic and Atmospheric Administration (NOAA) was also involved in computing and disseminating the data.
The speed of the NJIT operation was especially helpful to rescue workers. At the time, Richard Snay, a manager at the National Geodetic Survey, a division of NOAA, lauded NJIT for increasing the speed with which it recorded the locations of the planes. “Every second NJIT was retrieving data on the satellites and sending it on to the government, “ he said. “The increased data collection rates were especially critical for accurately positioning the aircraft to map the disaster sites.”