LiDAR Laser Maps Reveal Slide Risk
Maps created by an aerial scanning technique called LiDAR (lie-dar) reveal with stunning clarity a series of giant scars and piles of debris left by past landslides up and down the valley, including one more than twice as big as the monster that ripped loose Saturday, March 22, 2014.
LiDAR’s ability to peer beneath the region’s thick vegetation and lay bare the landscape has made it the go-to source on a wide range of geologic perils, from earthquake faults to flood zones.
But outside the circle of geologists, engineers and land-use experts, few people know the maps exist or how to access them. And though lidar can spot landslides that other surveys miss, counties are inconsistent in the way they incorporate the new information into their hazard planning.
“We’ve got all this great new data,” said University of Washington geologist David Montgomery. “But if you don’t have anybody to digest it and turn it into information that can get out to the public — it’s just nice data.”
BEFORE AND AFTER:
*Use the interactive tool above to compare lidar maps of the area before and after the slide. Puget Sound Lidar Consortium; Washington Department of Transportation
LiDAR uses ultraviolet, visible, or near infrared light to image objects. It can target a wide range of materials, including non-metallic objects, rocks, rain, chemical compounds, aerosols, clouds and even single molecules. A narrow laser-beam can map physical features with very high resolution.
LiDAR has been used extensively for atmospheric research and meteorology. Downward-looking lidar instruments fitted to aircraft and satellites carry out surveying and mapping – a recent example being the U.S. Geological Survey Experimental Advanced Airborne Research LiDAR. NASA has identified LiDAR as a key technology for enabling autonomous precision safe landing of future robotic and crewed lunar-landing vehicles.
Wavelengths vary to suit the target: from about 10 micrometers to the UV (approximately 250 nm). Typically light is reflected via backscattering. Different types of scattering are used for different liDAR applications: most commonly Rayleigh scattering, Mie scattering, Raman scattering, and fluorescence. Based on different kinds of backscattering, the LiDAR can be accordingly called Rayleigh LiDAR, Mie LiDAR, Raman LiDAR, Na/Fe/K Fluorescence LiDAR, and so on. Suitable combinations of wavelengths can allow for remote mapping of atmospheric contents by identifying wavelength-dependent changes in the intensity of the returned signal.