Two days after the landslide at Oso, Wash., a University of Washington scientist got a morning call from a radar company and research partner.
“You guys have a plane, we have a radar, is there anything we can do for the landslide in Washington state?” was the question by Yuly Margulis, the president of New York-based company Artemis Inc.
Gordon Farquharson, an engineer at the UW Applied Physics Laboratory, normally does aerial imaging over the oceans. But he consulted with UW colleagues who are geologists, obtained some discretionary funding from the APL, and obtained permission to fly a survey over the landslide site.
Farquharson and Chris Chickadel, an oceanographer at the APL, conducted two one-hour surveys, on Thursday, March 27, and Monday, March 31. They crisscrossed the site to take photos and then used image processing software to create a composite image.
“With thermal imaging we can tell where water is, so we can see the groundwater and saturation level, and measure the extent of the new river channel, and we can also measure the impounded water behind the slide,” Chickadel said. “It’s a way to map the changing nature of the slide as it’s going to evolve over the next weeks and months.”
Researchers are now processing their data, which will be made available to the public. They hope the two datasets could offer clues to the slide’s cause and evolution.
“It is critical to image the slide as soon as possible, because the mass will likely undergo rapid changes owing to continued movement, river action and seepage in the massive landslide deposition area,” said Joseph Wartman, a UW professor of civil and environmental engineering.
Wartman is co-leading a scientific investigation of the landslide that will incorporate data from the UW aerial surveys.
The team uses a Cessna 172 plane that is owned and operated by Regal Air, a flight school and charter company based at Everett’s Paine Field. Farquharson sat in the co-pilot’s seat to operate the equipment, which takes up the back half of the body of the plane.
Their equipment included an Artemis radar to measure topography, similar to one used by the UW group for imaging of coastal circulation and currents near river mouths. Cameras recorded visible light and thermal infrared wavelengths to map water inundation, groundwater seepage and slide extent.
Detection of movement in the soils near Oso could indicate areas of the slide that are still unstable. Data from immediately after the slide might show clues to what caused the slope to fail.
The Washington State Department of Natural Resources conducted similar aerial surveys using lidar technology to make precise topographic maps of rock and soil. Lidar is more sensitive than radar, but can have trouble with trees or in poor weather, Farquharson said, so the two datasets will be complementary.
The UW system is designed to be economical. The equipment is lightweight and the radar has a wide-angle view, both of which allow it to operate on small, low-flying planes. Researchers hope to explore the use of this system in taking more regular surveys of landslide risk areas, to monitor changes in groundwater and study changes in soils.
“I could see this technology might be useful for regular monitoring of landslide prone slopes,” Farquharson said.