Abstract
Abstract. Vegetation mapping in urban environments plays an important role in biological research and urban management. Airborne laser scanning provides detailed 3D geodata, which allows to classify single trees into different taxa. Until now, research dealing with tree classification focused on forest environments. This study investigates the object-based classification of urban trees at taxonomic family level, using full-waveform airborne laser scanning data captured in the city centre of Vienna (Austria). The data set is characterised by a variety of taxa, including deciduous trees (beeches, mallows, plane trees and soapberries) and the coniferous pine species. A workflow for tree object classification is presented using geometric and radiometric features. The derived features are related to point density, crown shape and radiometric characteristics. For the derivation of crown features, a prior detection of the crown base is performed. The effects of interfering objects (e.g. fences and cars which are typical in urban areas) on the feature characteristics and the subsequent classification accuracy are investigated. The applicability of the features is evaluated by Random Forest classification and exploratory analysis. The most reliable classification is achieved by using the combination of geometric and radiometric features, resulting in 87.5% overall accuracy. By using radiometric features only, a reliable classification with accuracy of 86.3% can be achieved. The influence of interfering objects on feature characteristics is identified, in particular for the radiometric features. The results indicate the potential of using radiometric features in urban tree classification and show its limitations due to anthropogenic influences at the same time.
Highlights
Mapping and characterizing vegetation and in particular single trees is important in forestry and urban management
Our study shows the potential of Full-waveform airborne laser scanning (FWF ALS) to classify trees at family level in urban environments
The comparison of the derived geometric and radiometric features demonstrates their applicability for taxonomic tree family classification
Summary
Mapping and characterizing vegetation and in particular single trees is important in forestry and urban management. Several studies indicate a high value of 3D vegetation description, e.g. in forestry (Hyyppä et al, 2012; Næsset, 2007), plantation (Fieber et al, 2013; Görgens et al, 2015) and urban areas (Höfle et al, 2012; Richter et al, 2013; Yan et al, 2015). In contrast to closed forest stands, urban trees are characterized by large species diversity within small areas and a complex (typically anthropogenic) shape
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