Canopy closure estimation in a temperate forest using airborne LiDAR and LANDSAT ETM+ data
Aims Forest canopy closure is one of the essential factors in forest survey, and plays an important role in forest ecosystem management. It is of great significance to study how to apply LiDAR (light detection and ranging) data efficiently in remote sensing estimation of forest canopy closure. LiDAR can be used to obtain data fast and accurately and therefore be used as training and validation data to estimate forest canopy closure in large spatial scale. It can compensate for the insufficiency (e.g. labor intensive, time consuming) of conventional ground survey, and provide foundations to forest inventory. Methods In this study, we estimated canopy closure of a temperate forest in Genhe forest of Da Hinggan Ling area, Nei Mongol, China, using LiDAR and LANDSAT ETM+ data. Firstly, we calculated the canopy closure from ALS (Airborne Laser Scanning) high density point cloud data. Then, the estimated canopy closure from ALS data was used as training and validation data to modeling and inversion from eight vegetation indices computed from LANDSAT ETM+ data. Three approaches, multi variable stepwise regression (MSR) random forest (RF) and Cubist, were developed and tested to estimate canopy closure from these vegetation indices, respectively. Important findings The validation results showed that the Cubist model yielded the highest accuracy compared to the other two models (determination coefficient (R) 0.722, root mean square error (RMSE) 0.126, relative root mean square error (rRMSE) 0.209, estimation accuracy (EA) 79.883% The combination of LiDAR data (c)Zhi Wu Sheng Tai Xue Bao Chinese Journal of Plant Ecology Zhang Rui Ying Deng Jie He Ji Zai LiDAR He LANDSAT ETM+Shu Ju De Wen Dai Sen Lin Yu Bi Du Gu Ce 103 doi: 10.17521/cjpe.2014.0366 and LANDSAT ETM+ showed great potential to accurately estimate the canopy closure of the temperate forest. However, the model prediction capability needs to be further improved in order to be applied in larger spatial scale. More independent variables from other remotely sensed datasets, e.g. topographic data, texture information from high resolution imagery, should be added into the model. These variables can help to reduce the influence of optical image, vegetation indices, terrain and shadow and so on. Moreover, the accuracy of the LiDAR derived canopy closure needs to be further validated in future studies.