Calculate change in canopy height over 10 years?

What is canopy height?

Canopy height models are a measurement of the height of trees, buildings, and other structures above the ground topography. This product is used in a variety of forestry applications including tracking vegetation and trees in a forest over time, calculating biomass, and estimating leaf area index.
 

How do you calculate CHM?

The Canopy Height Model (CHM), represents the heights of the trees on the ground. We can derive the CHM by subtracting the ground elevation from the elevation of the top of the surface (or the tops of the trees).