| The traditional remote sensing method is not sufficient to obtain the structural parameters of single wood directly,especially three dimensional structural parameters.The airborne LiDAR has a strong detection ability for the structural parameters of tree crown,so it can accurately obtain the three-dimensional structural parameters of the single tree crown.It is especially important to study the extraction of tree crown structure parameters and stand effective crown.Airborne laser radar technology is a new technology in the field of remote sensing,and it is the frontier of research.The development of LiDAR technology is very fast.compared with the existing traditional remote sensing methods,the penetration of LiDAR enables us to obtain more accurate DEM,DSM,crown growth state and other important parameters,and then extract the three-dimensional information of trees.This study was performed in Coniferous plantations in Maoershan experiment forest centre of northeast forestry university.Taking the artificial conifer species in the forest farm as the research object,combining with airborne LiDAR point cloud data,remote sensing image data and single wood parameter survey data from field surveys,the three-dimensional shape and structure parameters(treetop position,tree height,Crown diameter size,Crown height)of the single tree crown in the research area are extracted.And on this basis,the effective canopy is extracted to obtain the effective canopy of the stand.In this study,we use the local maximum window with variable window sizes to search the treetops of the crown,and to detect the treetops of individual tree crown and extract single tree height.The treetop is used as a marker,and the marker-controlled watershed segmentation algorithm is used to extract the crown width.Through the analysis the vertical point cloud elevation detection method to obtain the crown base height position,then the crown height to extract.At the crown boundary divided by the marker control watershed,the crown contact height is extracted,and the average value is taken as the effective crown height of the stand in the sample plot.Using this research method,the accuracy of tree isolation was 88.5%percent.The correlation analysis of the extracted values was carried out by using the measured data.The result shows that the R2 of tree height,crown diameter size and crown height is 0.8862,0.7864 and 0.8,in addition the precisions of 90.34%,86.8%,89.9%,respectively.The average contract height in the same forest stand is relatively stable.There was no significant difference in the effective crown height of the extracted stands by single factor analysis of variance.A local maximum algorithm can be used to extract tree crown vertex and tree height using by LiDAR.The variable size dynamic window is used to search for local maximum points.This method can improve the extraction accuracy of tree canopy structure parameters.Based on the tree top marker control watershed algorithm,high spatial resolution aerial photographs can be used as auxiliary data to extract the crown width with high accuracy.The vertical direction detection method can extract the single crown length efficiently.In the same forest,the effective canopy of the stand is roughly the same.LiDAR point cloud data can be used to extract effective forest canopy.The airborne LiDAR has the ability to extract the three-dimensional structure parameters of the single tree canopy,and can satisfy the extraction of the parameters of the single tree by the modern forestry survey and the extraction of the effective canopy of the stand. |
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