Abstract
ABSTRACTThe development of laser scanning technologies has gradually modified methods for forest mensuration and inventory. The main objective of this study is to assess the potential of integrating ALS and TLS data in a complex mixed Mediterranean forest for assessing a set of five single-tree attributes: tree position (TP), stem diameter at breast height (DBH), tree height (TH), crown base height (CBH) and crown projection area radii (CPAR). Four different point clouds were used: from ZEB1, a hand-held mobile laser scanner (HMLS), and from FARO® FOCUS 3D, a static terrestrial laser scanner (TLS), both alone or in combination with ALS. The precision of single-tree predictions, in terms of bias and root mean square error, was evaluated against data recorded manually in the field with traditional instruments. We found that: (i) TLS and HMLS have excellent comparable performances for the estimation of TP, DBH and CPAR; (ii) TH was correctly assessed by TLS, while the accuracy by HMLS was lower; (iii) CBH was the most difficult attribute to be reliably assessed and (iv) the integration with ALS increased the performance of the assessment of TH and CPAR with both HMLS and TLS.
Highlights
Over the last several decades, airborne laser scanning (ALS) demonstrated to be useful in providing accurate estimations of tree heights and forest attributes related to tree spatial arrangement (Hyyppä, Holopainen, & Olsson, 2012)
The results provided by TLS and ALS (TLSALS) and HMLS and ALS (HMLSALS) were equal to those obtained by TLS and held mobile laser scanner (HMLS) (R2 = 1) (Table 1)
Using eight FARO TLS scans for diameter at breast height (DBH) estimation, we obtained a bias of −0.41 cm and a root mean square error (RMSE) of 1.13 cm, very similar to the ones reported by Bauwens et al (2016) using five FARO scans, while with the ZEB1 HMLS we obtained a bias of −0.38 cm and a RMSE of 1.28 cm for DBH estimation, similar to what reported by Ryding et al (2015) and by Bauwens et al (2016)
Summary
Over the last several decades, airborne laser scanning (ALS) demonstrated to be useful in providing accurate estimations of tree heights and forest attributes related to tree spatial arrangement (Hyyppä, Holopainen, & Olsson, 2012). The development of laser scanning technologies is gradually modifying methods for assessing forest attributes in the field (Holopainen et al, 2013; Kankare et al, 2015; Moskal & Zheng, 2011). These technologies can improve work efficiency in forest inventory, potentially replacing manually measured tree attributes with more automatic procedures (Henning & Radtke, 2006; Liang et al, 2016). Especially the vertical distribution of forest vegetation, can be detected with high detail by laser scanners, providing single-tree estimations better than those obtained by remote sensing or traditional field measurements (Loudermilk et al, 2009). TLS data can be used to assess singletree attributes which can be hardly measured with other methods, such as tree architecture or detailed tree assortments (Dassot, Constant, & Fournier, 2011)
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