Community News

2018 0409 lidar map

There are two strange-looking depressions on top of a hill just east of the Baker Dam in Concrete. And evidence of a massive prehistoric landslide near Cultus Mountain, east of Mount Vernon. You wouldn’t know it from looking at aerial maps, though.

Near the Baker Dam all you see are trees, and the Cultus Mountain slide only shows up as a large depression – covered with more trees. But with Skagit County’s new Lidar story map and data, you can see all the way to the bare earth – to the complex, sometimes weird, and fascinating geologic features that make up Skagit County.

“The Lidar maps are pretty cool on their own, but we also use the data for a number of different purposes,” said Dr. Josh Greenberg, Skagit County GIS Remote Sensing Analyst. “We can see where rivers have historically changed course, we can determine changes in elevation height – for example, of riverbanks. It’s an incredibly valuable tool for flood modeling, as well as for examining landscape features around the county.”

Part of an ongoing partnership with the U.S. Geological Survey (USGS), the Lidar imagery was collected over the course of a year in 2016 and 2017.

“The Pacific Northwest is a difficult place to fly because you need leaves off the trees, no rain or wind, and no snow cover,” said Dr. Greenberg. “What we originally thought would take a few months ended up taking more than a year. We needed the right conditions for the entire region.”

Lidar systems are typically installed in airplanes, and emit infrared laser pulses that travel to the earth and back as the plane flies. A computer system calculates the time, location and height where the pulse hits an object or the earth. A secondary step allows the computer to remove trees, houses or other obstructions to show the bare earth. The final Lidar map allows users to see areas of the ground that are usually hidden in aerial images.

Skagit County first began partnering with the USGS in 2005, when Lidar was still in its infancy. Interest in Lidar maps picked up significantly in 2014, following the SR 530 slide in Snohomish County, when the state Legislature directed the Department of Natural Resources to collect improved Lidar data for assessment of potential landslide dangers, among other projects. Dr. Greenberg teamed up with Dr. Jon Riedel of the National Park Service to create the county’s story map.

To view the LIDAR story map, visit www.skagitcounty.net/LidarMap. To find out more info about Lidar data, visit https://www.skagitcounty.net/lidar.