Image-based estimation of crown volume of individual street trees by plane calculation of angle disparity

Abstract

Street trees provide significant and widespread environmental benefits to the city and its citizens, such as improved air quality and adaptation to climate change. Crown volume (CV) indicates the geometric volume of crown, which is an essential indicator for the ecological service evaluation of street trees. The measurement of CV makes it possible to assess the carbon storage and input cost of urban trees. Because of the particularity of crown shape of street trees, the existing two-dimensional methods of calculating CV of forest trees become difficult except the three-dimensional techniques through the unmanned aerial vehicle, LiDAR equipment, and traditional harvest methods. In this study, a new virtual research method for plane calculation of angle disparity (PCAD) is proposed to calculate the CV of street trees. Two temporal satellite images of the exact location were first collected from Google Earth Pro, and then the angle disparity of images was adopted as a starting point to calculate tree height. Finally, CV was calculated from tree height, stem height, and crown diameter. The feasibility of the method was verified by a sample survey of street trees in Shanghai, China and the relative error of CV calculation by PCAD compared to that by field survey was 17.31 %. PCAD has the advantages of low-cost, quick operation, and suitability for a large area in studying CV of street trees.