PARENT SESSION
Wednesday, August 9, 5:00-6:30 pm
Poster Session 18 - Forest ecology and management
Exhibit Hall, Ballroom Level, Cook Convention Center

Determining forest canopy structure with a laser rangefinder: split beams and measurement accuracy.

Pedersen, Brian^*,1, Hanifin, Robert¹, ¹ Dickinson College, Carlisle, PA, USA

ABSTRACT- The spatial distribution of aboveground plant parts influences the ability of vegetation to absorb solar energy and provide habitat. In forests, canopy structure can be determined from the ground by measuring distances up to canopy elements with a laser rangefinder and applying the Beer-Lambert Law. This approach assumes the distance probe has an infinitesimally-small cross-section. However, the beams of laser rangefinders have a finite cross-section that may be split by canopy elements. We tested a laser rangefinder (Leica Disto Classic3) in the laboratory to determine how it performs when the laser beam is divided between two targets at different distances. We also developed Monte Carlo simulations of a beam's penetration of various broad-leaved forest canopies. The simulations considered dispersion of the beam (e.g., the cross-section is 0.08 cm² at the instrument face and 1.76 cm² at 30 m). The model results indicate that split beams are common. For example, in a forest of identical leaves with a one-sided area of 78.5 cm² and margin length of 62.8 cm, and a leaf area index of 4 distributed evenly throughout a 30 m high canopy, 33% of beams will be split. The laboratory tests indicated that when the rangefinder's beam was split, 13% of the resulting distance measurements were in error. Additional simulations will indicate the impact of erroneous distance measurements on the accuracy of canopy structure measurements.

Key words: forest, canopy structure, laser rangefinder