A combined GLAS and MODIS estimation of the global distribution of mean forest canopy height

An inter-comparison among three global forest height maps [the present study, Lefsky (2010), and Simard et al. (2011)] was implemented in a pixel-by-pixel manner. High agreement (R2 = 0.73, RMSE = 4.49 m) was determined between the present study and Simard et al., whereas the result from Lefsky was notably different from the other two results (R2 = 0.14, RMSE = 8.92 m, compared with the present study; R2 = 0.11, RMSE = 11.19 m, compared with Simard et al.). Large disparities were generally associated with evergreen broadleaf forests in South America, deciduous needleleaf forests in Europe and Russian North Asia, and evergreen needleleaf forests on the West Coast of North America. Differences in the height metric were a main factor affecting the disparities among the three results. Validation against field survey data acquired from the Distributed Active Archive Center indicated the accuracy of our mean forest canopy height map (R2 = 0.63, RMSE = 4.68 m, n = 59).