Remote Sensing Estimation of Stand Parameters in a New Chinese Fir Plantation From UAV Three-Dimensional Information

A new plantation of Chinese fir(Cunninghamia lanceolata) in Pushang national forest farm, Shunchang county, Nanping city was used as the study object. The flight was conducted twice for UAV imagery collection using a Phantom 4 Multispectral. The Digital Surface Model(DSM) from UAV imagery was used to derive Canopy Height Model(CHM) in the study site. Then according to the algorithms of local maxima and watershed segmentation, the tree height and tree crown were detected from the CHM. At the same time, 15 standard sites were established in the study site. A measuring rod was used to measure all Chinese fir heights and north-south crown sizes. Taking the randomly selected 265 Chinese firs in the field with corresponding accurate positions to trees on the UAV imagery as the field data for tree-level, and the average tree height and average north-south crown size in each standard site as the field data for stand-level. Then the accuracy of remote sensed tree height and tree crown detection of Chinese fir was evaluated from the tree-level and stand-level, respectively. The accuracy of estimated tree height between the two flight operations were 90.86% and 91.34%, respectively, and the accuracy of estimated north-south crown were 83.55% and 83.95%, respectively. For the tree-level, tree height assessment yielded R²=0.89, RMSE=22.37 cm, and EA=91.00%; north-south crown assessment yielded R²=0.70, RMSE=27.33 cm, and EA=82.22%.At the stand-level, R²=0.95, RMSE=12.27 cm, and EA=94.61% for tree height assessment; R²=0.82, RMSE=11.24 cm, and EA=92.20% for north-south crown assessment. The average remote sensed tree height was 0.07 m lower than the average field measurement tree height, and the average north-south crown size was 0.04 m lower than the average field measurement tree height. The results highlight that UAV 3D scene can accurately estimate the height and tree crown of Chinese fir in the study site, and the estimation accuracy is similar between different areas and flight batches in the case of the same flight parameters. It can provide a reference for rapid, effective monitoring of newly planted Chinese fir, and scientific forest management.