Accuracy of a high-resolution lidar terrain model under a conifer forest canopy

Airborne laser scanning systems (commonly referred to as light detection and ranging or lidar systems) can provide terrain elevation data for open areas with a vertical accuracy of 15 cm. Accuracy in heavily forested areas has not been thoroughly tested. In this study, a high-resolution digital terrain model (DTM) was produced from high-density lidar data. Vegetation in the 500-ha mountainous study area varied from bare ground to dense 70-year-old conifer forest. Conventional ground survey methods were used to collect coordinates and near-ground vegetation heights at 347 ground checkpoints distributed under a range of canopy covers. These points were used to check the DTM accuracy. The mean DTM error was 0.22 +/- 0.24 m (mean +/- SD). DTM elevation errors for four tree canopy cover classes were: clearcut 0.16 +/- 0.23 m, heavily thinned 0.18 +/- 0.14 m, lightly thinned 0.18 +/- 0.18 m, and uncut 0.31 +/- 0.29 m. These DTM errors show a slight increase with canopy density but the differences are strikingly small. In general, the lidar DTM was found to be extremely accurate and potentially very useful in forestry.