This split image shows two different digital models of a forest in California: a digital surface model (DTM) and a digital terrain model (DTM). These models were used to derive the height of the tree canopy.

The models were created from a LiDAR (light detecting and ranging) dataset. LiDAR uses a laser scanner and positioning systems mounted in an aircraft (generally a plane or helicopter). The laser emits rapid pulses of light and the time it takes for that light to return to the aircraft is measured. Because the light is returning to a moving aircraft, the positioning systems are used to compensate for where the craft's position is when it sends the light down and where the craft is when the light is returned. Some of the light emitted hits the tops of trees, some hits lower branches, and some hits the ground, like sunlight filtered through the trees. The collection of pulses returned create a point cloud.

ArcGIS Pro was used to convert the LiDAR point cloud into a digital surface model (DSM), which includes all points in the point cloud, and a digital terrain model (DTM), which uses only those points that hit bare ground. From these two models, the height of the trees is calculated by subtracting the DTM from the DSM, resulting in the canopy height model (CHM).

Technology like this can be used to estimate aboveground biomass (all parts of the tree except the roots), from which forest carbon sequestration is derived.

Image credits: Surface & Terrain Models, J. Frauman. 3D Model: U.S. Geological Survey, 2019, USGS 3D Elevation Program Digital Elevation Model. LiDAR Data Citation: U.S. Geological Survey, 20250515, USGS 1/3 Arc Second n40w121 20250514: U.S. Geological Survey.