Canopy height can be measured using direct or indirect methods. The important point is to get representative data for the canopy under consideration. Based on the type of canopy (herbaceous / woody), methods for canopy height measurement can be categorised as follows:
Most of the methods for herbaceous (including grasslands) canopies have been developed over many years for livestock farmers to get rapid and frequent estimates of pasture height (which indirectly relates to biomass). Some common methods have been listed below:
Some more information can be found here
Similar to pastures there are simple methods for rapid and reliable woody vegetation height measurements as follows:
Some more information about these methods can be found here
There are number of smartphone apps that measure angles required in above listed methods and can be exploited to measure tree heights (example: Theodolite, Seelevel, carpenter app, Clinometer). In fact some apps have been developed specifically for tree height measurements – baumhoehenmesser, iHypsometer Lite, Measure Height. However, details comparison of these apps needs to be done.