Silvilaser 2019 - Poster Presentations »
A comparative assessment of the area-based approach and individual tree detection for volume estimation in mixed temperate forests using Airborne Laser Scanning data
The study presents the steps taken so far to develop a method for assessing the stand volume based on Airborne Laser Scanning (ALS) data for mixed forest stands in the temperate climate of southwest Romania. For this purpose, several dendrometric parameters (i.e. height, dbh) were extracted or predicted from ALS data by the use of two methods, individual tree detection (ITD) and area-based approach (ABA), respectively. A computer-assisted field inventory system (Field Map) together with a high accuracy GNSS receiver and a Vertex inclinometer were used to collect the reference ground data from four one-hectare (100 x 100 m) mixed tree species plots. The main tree species within each plot are Norway spruce (Picea abies) and Beech (Fagus sylvatica). For the ITD approach ALS data were used to extract the digital terrain model (DTM), digital surface model (DSM) and the normalized canopy height model (CHM). A local filtering algorithm with a canopy-height based variable window size was applied to identify the position, height and crown diameter of the individual tree within each plot. The dbh was predicted by a linear regression model that relates field dbh for each tree with their corresponding ALS-derived tree height and crown diameter. The ALS-predicted dbh and the derived tree height were used for tree volume computation, and the stand volume is calculated as the sum of the individual trees’ volumes inside each plot. The overall root mean square error (RMSE) calculated for all the plots between field measured tree volume and their corresponding tree volume identified using the ITD method was 0.48m3. The ABA method consists of using regression models for the estimation of stand volume directly from the ALS point cloud metrics. In this study the predictor ALS variables were height percentiles (hp20, hp60, hp80) and canopy relief ratio. The total wood volume of the identified trees based on ITD method represented 52-71% from the total volume calculated by field measurements and specific methods. In the case of ABA, the total wood volume predicted based on represented, for one plot, 91% from the total volume calculated by field measurements. The results of the ABA methodology applied in the mixed temperate forests of Southwest Romania indicate a better estimation of the total wood volume than the one obtained by use of ITD method.