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Using LiDAR to Measure the Urban Forest in DeKalb, Illinois



We present the results of an experimental comparison of existing and new methods to estimate tree height from LiDAR data and to subsequently estimate tree diameter allometrically from species and height. Ground truth of tree height was established using a LaserAce Rangefinder to directly measure the height and diameter of a sample of 952 parkway trees. Based on this sample, it was possible to directly calculate the accuracy and error budget for the LiDAR and allometry-derived metrics. The results can inform the optimal estimation techniques and expectations of accuracy for biogeographers studying urban forests.
... Airborne laser scanning. or lidar, uses laser pulses emitted from a sensor to precisely measure urban structure, including tree structure, and has reduced the time required to survey an area (Edson and Wing, 2011;Moskal and Zheng, 2012;Hunter et al., 2013;Pingel and Bergman, 2017 ). A substantial benefit of ALS is that scans can penetrate through the tree canopy to the ground (Wallace et al., 2016). ...
... The ALS point cloud functioned as the base for subsequent geo-referencing and alignment of the other datasets. A manual tree survey of approximately 1000 parkway trees was conducted in 2015 and compared to the 2009 lidar data (Pingel and Bergman, 2017). This evaluation was used a basis of comparison for the SfM data collected for this study. ...
... Tree points were separated from the point cloud using previously identified and updated tree locations (Pingel and Bergman, 2017) to create a 10 m buffer that drove a "clip" operation using the "lasclip" tool in LAStools (Rapidlasso GMBH, Gilching, Germany), since extraction from the full (point size) cloud was computationally inefficient. This also allowed for a manual inspection and review of the tree points using CloudCompare (CloudCompare 2.10 Zephyrus Stereo, 2018) before further processing. ...
Urban forests are dynamic and change in response to both human and natural forces. To effectively monitor and manage urban forests, periodic inventories are needed to ensure that information about them is current and comprehensive. This task has traditionally been accomplished by manual ground-based field surveys, or more recently using GIS techniques utilizing remote sensing products, especially lidar. Low-cost Unmanned Aerial Vehicles (UAVs) employing Structure from Motion (SfM) techniques have the potential to augment these sources for urban forest inventories. We present the results of an analysis of approximately 1000 urban trees and compare accuracy in the measurement of tree heights and diameters from manual measurements, lidar, and Structure from Motion (SfM) from UAV-based imaging. Results indicate that in an urban environment, the SfM method produces estimates of tree height (R² = 0.96; RMSE =1.91 m) and diameter (R² = 0.98; RMSE =3 cm) comparable to manual field measurement, and better than those derived from conventional aerial lidar. In addition, the gains in accuracy from SfM come largely from younger, smaller trees that are often poorly imaged with lidar.
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