Optical stereo vs LiDAR for canopy height models

Every forester who's asked a remote sensing vendor for a canopy height model has heard both pitches. One says fly LiDAR, get a point cloud, done. The other says run stereo pairs through a photogrammetry pipeline and get almost the same surface for a fraction of the campaign cost. Both are telling the truth about their own method. The real question for a REIT asset manager or a carbon project developer is which one fits the reporting cycle you're working against.

How each method builds the surface

LiDAR fires pulses through gaps in the canopy and records returns off leaves, branches, and bare ground. Enough of those pulses make it to the forest floor that you get two things from one flight: a digital terrain model (DTM) built from ground returns, and a digital surface model (DSM) built from canopy returns. Subtract one from the other and you have a canopy height model with the ground survey baked in. That's the appeal. It's also why LiDAR flights are expensive and get scheduled once every five to ten years on most timberland, not annually.

Optical stereo works differently. Two or more overlapping passes of the same ground, shot from slightly different angles, let you reconstruct a surface model through photogrammetry the same way your eyes reconstruct depth from two viewpoints. The catch is that passive optical imagery can't see through a closed canopy to the ground underneath, so a stereo-derived DSM needs a DTM from somewhere else, usually an existing bare-earth model from a prior LiDAR acquisition, state LiDAR program, or SRTM-class source. Stereo gives you the top of the canopy, reliably and repeatably. It was never going to give you the ground.

Photogrammetry vs LiDAR canopy height: what changes year to year

Here's where it matters for a standing-volume program instead of a one-time survey. A DTM doesn't move. Bare earth is bare earth whether you captured it in 2019 or 2024, short of a landslide or a logging road cut. Canopy height is the variable that actually tracks growth, thinning, blowdown, and harvest. So once a parcel has a usable DTM on file, you don't need to re-fly LiDAR every year to watch standing volume change. You need a new canopy surface, and that's exactly what a stereo pass gives you at a fraction of the cost and on a cadence a LiDAR campaign can't match.

This is also the honest limit of stereo. In dense, multi-layered stands, LiDAR's multiple returns still resolve sub-canopy structure, understory height, and gap fraction that a single optical surface can't see past the top layer. If your project depends on characterizing vertical stand structure rather than top-of-canopy height and volume, that's a LiDAR question, not a stereo one. Stereo imagery read for forest structure answers "how tall is the canopy now, and how has that changed since last year's pass," which is the number that feeds a standing-volume regression and a valuation cycle.

Where this lands for a holding or carbon project area

Put plainly: LiDAR earns its cost as the baseline, the ground truth you calibrate against. Stereo earns its keep as the thing you refresh every reporting period without re-running a flight campaign. A timberland REIT doesn't need a new ground survey every year to know whether a compartment gained volume. A carbon project developer monitoring a defined project area for a reporting period needs an update that holds up against last year's number, not a brand-new terrain survey each cycle.

Canopy Height Mapping builds the canopy surface from overlapping VHR optical stereo passes and regresses it to a standing-volume estimate for your holding or project boundary, refreshed on an annual cadence, without a new ground LiDAR flight. If your parcels already have a usable terrain model on file and you need this year's volume number without re-flying the ground, take a look at how the pilots run.