Abstract: [Objective] In order to provide technical support for the investigation of gap structure parameters, the LiDAR technology was used in this study to identify the gap structure parameters(including gap size, canopy height and gap shape index).[Method] Taking the airborne LiDAR as the data source, the 54 gaps in the five gap investigate plots were set up in the Mao'ershan experimental forest farm of Northeast Forestry University as the study area, The canopy height model was obtained by comparing the five interpolation method (ordinary kriging, inverse distance weight, splines, natural neighbor, local polynomial)to determine the optimal interpolation method. The canopy height model was used to identify and extract the gaps by alternative sequential filter.[Result] By comparing the RMSE of the five interpolation method, it is found that the ordinary kriging method is suitable for interpolating DEM, and the inverse distance weight method is suitable for interpolating DSM. The gap recognition rate was 92.6% when the gap was extracted by alternating sequential filter. Using the paired test method to check the gap size, canopy height with field survey data, linear correlation was observed between the values of LiDAR estimation and field investigation, and the R² values of gap size and canopy height case were 0.983 and 0.737,respectively. Compared with field survey data, the average relative error of extracted gap size was 15.78% and canopy height was 11.94%.[Conclusion] Using alternating sequential filter based on airborne lidar data can effectively identify the gap and accurately extract its structural parameters. Interpolation accuracy of the canopy height model is affected by the slope, slope position and the complexity of the canopy structure; gap size is affected by boundary shape and forest structure, canopy height as the terrain gradient increases, the error increases. The airborne LiDAR technology has the advantage of acquiring three-dimensional structural information of terrain and trees, this study provides a new remote sensing method for the identification of gaps and the extraction of gap structure parameters.

Key words: light detection and ranging(LiDAR), gap structural parameters, mathematical morphology, CHM