New airport survey method takes flight
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(Left to right): Photos, discrete lidar and waveform lidar point-clouds of common airport obstructions—a tree (top) and tower (bottom)—showing the achievable point density increase using full-waveform data.
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irports need regular area surveys to map out possible obstructions that could affect construction, tree maintenance or runway approach patterns. A promising alternative to expensive physical surveying is airborne light detection and ranging (lidar).
Christopher Parrish, a civil and environmental engineering graduate student, is studying lidar, and he sought advice from ECE McFarland-Bascom Professor Rob Nowak. Together, Nowak and Parrish developed a new workflow for processing data from waveform lidar by taking into account models for both distortion and signal characteristics.
The approach resulted in a robust, reliable obstruction mapping method that addresses previous challenges while simplifying workflow. Parrish applied the new methods to lidar signals collected around the Madison area with great success, and the two published their results in the May 2009 issue of the Journal of Surveying Engineering.
“This is a huge advance,” says Nowak. “It totally revolutionizes how well they are able to do these automatic airborne surveys of airports.” Parrish estimates a 46-percent decrease in total obstruction survey completion time and a 38-percent decrease in human labor time, according to the most recent National Oceanic & Atmospheric Administration National Geodetic Survey (NGS) lidar obstruction survey.
Lidar works similarly to radar but uses laser light as its signal. As a surveying plane flies over an area officials want to map, it sends out a laser pulse. Sensors on the plane detect the signal as the laser reflects off the surfaces it encounters. Then, engineers collect data from all the beams that scanned a particular point in space and map all the detected reflections in a scatterplot. Officials can use the resulting point clouds to determine the shape, size and location of obstructions.
NGS has researched lidar for the past decade. Traditionally, NGS has used discrete data, focusing on only the initial return of each laser pulse, or the “front edge” of the return signal. Now, systems can digitally acquire and save the entire laser return, a process known as waveform lidar, which results in scatterplots with an average of 252 percent more data points than traditional methods.
“Traditional methods focus on what happened to the signal and the process that distorts it, but they ignore the physical characteristics of the signal itself,” says Nowak. The new obstruction mapping method could be applied to a variety of signals that are distorted, incomplete or noisy. One example is MRI, which Nowak says is a great example of how the new method could make a big difference beyond airports.
