Abstract
Abstract. Lidar (light detection and ranging) data are becoming more and more important in the analysis of the most relevant forest parameters. This study aims to compare the most recent segmentation methods for single trees using the ALS (Airborne Laser Scanning) point cloud and the CHM (Canopy Height Model). The methods used were the Li et al., method developed in 2012 and the Multi CHM method developed in 2015. The parameters analysed were the height and diameter for the individual trees and the volume and density for the entire forest. The efficiency of each method was verified by comparing the estimated parameters with those measured through 30 test areas. To better identify the useful parameters for the correct calibration of the algorithms, the population was divided into three layers according to the vertical structure and chronological class. From the comparison of the volumes obtained with the above methods and those calculated for the test areas, it emerges a tendency to over-segment for the Multi CHM method, while for the appropriately calibrated Li method there is a better correspondence to reality. The F-score values for the volumes obtained for the Li method are between 0.52 and 0.69 while for those obtained for the Multi CHM method are between 0.47 and 0.55. When compared with relascopic measures for each of the 48 parcels, a mean absolute difference ∼127 m3/ha and ∼141 m3/ha were found for Li2012 and MultiCHM respectively.
Highlights
IntroductionNowadays lidar technology is used in the drafting of forest management plans mainly as support in the stratification of the stand in forest units and in the verification of the parcel boundaries (Leckie et al, 2003)
Lidar data are becoming increasingly important in the analysis of the Earth surface (Pirotti, 2019) and in particular the main forest parameters.Nowadays lidar technology is used in the drafting of forest management plans mainly as support in the stratification of the stand in forest units and in the verification of the parcel boundaries (Leckie et al, 2003).The estimation of volumes is currently carried out by methods based on the estimation of the basimetric area and its conversion into volumetric parameter
In literature errors from relascopic measures are between 4 and 10%, with higher error values for uneven-aged dense forests (Pesonen et al, 2009; Piqué et al, 2011). Our area included both even-aged and multi-strata forests, we can assume an error in relascopic measures in the higher range. Accounting for this factor is important; it does not decrease the validity of the method, but clarifies that differences do not necessarily imply that one method is better, but how close it comes to a more common estimation method, i.e. sample relascope areas
Summary
Nowadays lidar technology is used in the drafting of forest management plans mainly as support in the stratification of the stand in forest units and in the verification of the parcel boundaries (Leckie et al, 2003). The estimation of volumes is currently carried out by methods based on the estimation of the basimetric area and its conversion into volumetric parameter. These methods consist of measuring diameters for the whole forest or for test areas or the relascopic technique. The importance of knowing the volume of a stand is fundamental for a correct planning that guarantees the opportunity to use the woody products without depleting the wooded areas. Optical and radar imagery are often used together (Vaglio Laurin et al, 2016)
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