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What is the difference between lidar data and a digital elevation model (DEM)?

Light detection and ranging (lidar) data are collected from aircraft using sensors that detect the reflections of a pulsed laser beam. The reflections are recorded as millions of individual points, collectively called a “point cloud,” that represent the 3D positions of objects on the surface including buildings, vegetation, and the ground. 

Digital elevation models (DEMs) are one of many products that can be derived from lidar data, though they can also be derived from other sources. DEMs are digital representations of the earth’s topographic surface. They’re a “bare-earth” product because they do not include surface features like buildings and vegetation. 

A high-resolution DEM can be derived from lidar point-cloud data by stripping away the surface features and sampling the ground elevation in uniform increments to produce a bare earth model. 

The USGS is in the process of replacing all of our legacy DEMs with DEMs derived from lidar and IfSAR (Alaska only) data. 

Learn more: 

Divided image with tree-covered slope on one side and the treeless, bare earth on the other side revealing landslides
By processing lidar point clouds (left) to bare earth DEMs (right), the vegetation is stripped away to reveal past landslides and steep slopes at risk of failure masked by forested canopies. In dense forests, landslides--especially old landslides--might be invisible on aerial images and hard to detect from the ground.

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