Leaf orientation（ including inclination and azimuthal angle） distribution of forest canopy determines the internal and below-canopy solar radiation regimes and influences the efficiency of forest photosynthesis and the characteristics of canopy bidirectional reflectance. This study develops a method to retrieve leaf orientation distribution of an artificial tree by combining Terrestrial Laser Scanning（ TLS） data and computational geometry technique and then evaluating the effectiveness of the proposed method. In this study

a manmade broadleaf tree was set up to acquire point cloud data using a terrestrial laser scanner（ Leica Scanstation 2）.We successively placed the terrestrial laser scanner at six different locations on a circle with an azimuthal angle interval of 60° to acquire comprehensive point cloud data of the artificial tree. The different point cloud datasets obtained from different scan locations were registered into a common coordinate system. Point data of 78 comprehensive leaves were manually selected to validate the proposed method. Inclination angle of points was obtained through reconstructing the normal vector of a point within a certain neighbor region with six points. We then computed the azimuthal angle of points by finding the direction of the principal axis of the leaf where the point belonged to. Computer-based results were compared with manual-based measurements to evaluate the proposed method. The inclination and azimuthal angles of each leaf can be computed by averaging the inclination and azimuthal angles of points belonging to the leaf. The inclination angles of wrinkling leaves were measured separately for two to three subsections by assuming that the surface of each subsection was nearly plane. Therefore

for inclination angle

a subsection was regarded as a single leaf. The histogram of the computing results accurately reflected actual leaf orientation distribution. Leaf inclination angles mainly distributed from 40° to 90°

and azimuthal angles mainly peaked within the range of 80° to 160° and 280° to 320°

which were similar to the manual results. In terms of single-leaf comparison

for leaf inclination angle

R2 was 0. 88（ N = 209

p <0. 001）; for leaf azimuthal angle

R2 was 0. 97（ N = 78

p < 0. 001）. However

inclination angles were overestimated for the range of 0° to 50° and underestimated for the range of 70° to 90°. An effective method for the accurate retrieval of leaf orientation distribution from TLS data was proposed. This method provides a theoretical foundation and approach for accurately obtaining canopy three-dimensional spatial distribution

consequently improving the estimates of extinction coefficient and leaf area index. However

the method has not been applied to all tree species. The inclination angle computation works well for broadleaf species

and the azimuthal angle computation is suitable for broadleaf species with a leaf length usually longer than the corresponding width. Meanwhile

computation for azimuthal angle is under the assumption that a leaf principally points to below the horizontal plane. Considerable research about inclination and azimuthal angle distribution of other tree species remains to be explored.