Seeing Under the Cedar: Canopy Height & Bare Earth

A photo map sees the tops of things: cedar canopy, oak crowns, brush along a fence line. It can't see the dirt underneath.

On Hill Country land, your terrain, drainage and volumes all depend on that dirt. A LiDAR scan reaches it.

Two surfaces, not one

LiDAR pulses slip through gaps in the foliage, some reaching the ground, so one scan builds two surfaces:

• DSM — Digital Surface Model: the top surface, following treetops, brush and rooftops.
• DTM — Digital Terrain Model: the bare earth, with vegetation and structures stripped away.

Every terrain and drainage layer is built on the DTM (see Reading Your Terrain Layers and Where the Water Goes). Without LiDAR, they would follow the treetops and get the drainage wrong.

The Canopy Height Model (CHM)

What it is: subtract the bare earth (DTM) from the top surface (DSM). What's left is the height of the vegetation, cell by cell: the Canopy Height Model.

It reads near zero over open pasture, low over young cedar and tall under a mature oak motte.

When to use it:

• Brush and cedar management — see where the heavy canopy is and what clearing involves. Fly again afterward and compare.
• Fuel load and fire planning — find dense canopy near structures.
• Habitat and pasture planning — tell open grazing land from brushed-in acreage.
• Trusting your terrain data — the CHM shows the LiDAR separated canopy from ground.

Why it beats a photo map

A photo-based elevation model drapes over the brush; it can't measure ground it can't see. LiDAR reaches through canopy gaps, so the bare earth and everything built on it hold up on wooded land.

Where brush is heavy, make sure your package includes a LiDAR scan (see Point Cloud (LiDAR)).

The honest limit

Canopy height and bare earth come from your elevation data like the terrain layers, with the same limit. Drainage, flow, terrain, and floodplain layers are derived analysis computed from our elevation data to support planning and design. They are not a certified survey, a stamped engineering study, or a FEMA flood-zone determination. Boundary and title work needs a licensed Texas surveyor; we don't do that work.