Abstract
In present paper 3-D remote sensing of woody canopy heights using a new scanning helicopter-borne lidar system with high spatial resolution was examined. This lidar system was characterized by (i) almost ground surface was covered by scanning a laser beam of small-footprints below tens of centimeters, (ii) precise grid data were obtained by rectangular scan using a garbomirror scanner, and (iii) there were two operational modes, first pulse mode (FP-mode) for measuring woody canopy and last pulse mode (LP-mode) for measuring ground level, of time interval meter measuring the elapsed time between the laser pulse emission and the return of the reflected pulse.
FP-mode DEM (Digital Elevation Model, grid interval=33.3 cm) and LP-mode DEM were calculated from data measured by FP-mode and LP-mode. DSM (Digital Surface Model) was computed with an error of about 15 cm from the LP-mode DEM. Mesh data (DCHM) of woody canopy heights were obtained by subtracting the DSM from the FP-mode DEM.
The laser-derived tree heights of 14 coniferous trees and 6 broadleaf trees estimated from the DCHM were in error by less than 47 cm (RMSE=19 cm) in comparison with the ground measured tree height. The median filter (3x3 mask) was effective for removal of spike noise in the DCHM. The result showed the accuracy of tree height estimate was extremely improved by the mentioned method using the scanning lidar system with high spatial resolution.
