| Gap is a form of interference in the forest ecosystem,the identification of gaps and the extraction of structural parameters are the basis of studying the theory of forest cycle and revealing the relationship between gap and forest structure,species composition and biodiversity.Remote sensing technology has been applied to gap identification,especially laser radar technology,so this study uses the lidar technology to identify the gap structure parameters(gap size,canopy height and gap shape index).Taking the airborne lidar as the data source,high resolution remote sensing images as auxiliary verification data,the 54 gaps in the five gap investigate plots were set up in the Maoershan Experimental Forest Farm of Northeast Forestry University as the study area,The canopy height model was obtained by comparing the five interpolation methods(ordinary kriging,inverse distance weighted,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.By comparing the RMSE of the five interpolation methods,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 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%.This method is extended to the large scale,the gap is still good recognition effect.Using alternating sequential filter based on airborne lidar data can effectively identify the gap and accurately extract its structural parameters,This study could provide technical support for the investigation of gap structure parameters. |
