New aerial images of the Oso landslide show the topography of the debris field in unprecedented detail.
The images were commissioned by the Washington State Department of Transportation and are based on a laser-surveying technique called lidar — light detection and ranging. In the survey, a plane equipped with a laser scanner flew over the area, firing thousands of light pulses per second. The system builds a three-dimensional map of the surface based on how long it takes those pulses to bounce back.
Sophisticated software weeds out signals that bounce off trees and structures, essentially peeling away the vegetation to reveal the terrain below. Elevations in lidar maps are accurate to within a few inches.
State and federal geologists are analyzing the image to calculate the volume of the slide and as a baseline to compare to future images to detect any ground motion or deformation.
A zoomable version is available here.