Two-dimensional Forest Canopy Architecture from Terrestrial Laser Scanning

Terrestrial laser scanners (TLS) are now capable of collecting 3d data clouds consisting of the x,y,z coordinates of several million laser hits, plus information on return intensity and, in some cases, target colour. TLS collect data at sub-centimetre resolution at a range of zenith view angles. This paper describes the results of a series of experiments in which a TLS was used to measure the twodimensional structure of a broadleaf deciduous woodland canopy at a range of dates with different leaf cover. The TLS was mounted on a tripod and oriented to measure canopy gap fraction over a near-complete hemisphere. The laser data were compared with nearsimultaneous hemispherical photographs of the canopy taken at the same location. Comparison of the hemispherical photography and TLS data showed that, in contrast to our earlier work in needle-leaf canopies, the TLS underestimated canopy directional gap fraction. The explanation of this difference is explored and alternative approaches to measure gap fraction from laser scanner data are suggested.