| dc.description.abstract | Diameter at Breast Height (DBH) is the measure of the diameter of a tree stem 1.3
meters above the ground. DBH is a key variable measured in Forest Resource
Inventories (FRIs) and is traditionally measured manually, which is labour-intensive.
The 2020 Apple iPad Pro 12th Generation is a lightweight, consumer-level tablet with an
integrated LiDAR scanner with a maximum range of 5 m and a positional accuracy of
±1 cm. The overall objective was to examine the feasibility of estimating DBH in boreal
forests with iPad Pro LiDAR. A scoping study was conducted in a plantation forest
(48.37°N, 89.39°W) near Thunder Bay, ON, Canada, with the specific objective of
determining an optimal method for DBH estimation with the iPad Pro. Different
combinations of scanning methods (i.e., circular, figure-8, transect), numbers of stem
cross-sections (i.e., one or five), sizes of stem cross-sections (i.e., 4 or 10 cm), and curvefitting formulas (i.e., Pratt’s circle fit, Taubin’s circle fit, Taubin’s ellipse fit, Szpak’s
ellipse fit) were tested to identify the combination producing the most accurate
estimates of DBH. The optimal method was the circular scanning pattern with a single 4
cm cross-section and a combination of circle- and ellipse-fitting formulas (RMSE = 1.1
cm; 6.2%). The second specific objective was to determine the accuracy of DBH values
estimated with the optimal method in natural boreal forests. DBH was estimated for 133
trees on 15 sites in northern Ontario, Canada, representing a range of natural boreal
forest site conditions. A secondary objective was to determine if the tested stand- (i.e.,
species composition, age, density, understory density) or tree-level attributes (i.e.,
species, actual DBH) significantly impacted the accuracy of estimated DBH values. An
RMSE of 1.5 cm (8.6%) was achieved. Estimated DBH was within 1 cm of actual DBH
for 78 of 133 (59%) measured trees. Stand age had a large effect (> 0.15) on the accuracy
of estimated DBH values, while density, understory density, and actual DBH had
moderate effects (0.05-0.15). In both studies, Inertial Measurement Unit (IMU) and
positional accuracy errors with the iPad Pro LiDAR scanner limited the accuracy of
DBH estimates. Future studies should incorporate a greater number of natural boreal
forest sites to better understand the impacts of different stand and tree attributes on the
accuracy of estimated DBH values. Future studies should also compare the accuracy of
DBH values estimated from the iPad Pro and those estimated from traditional MLS and
TLS for the same sites to identify the trade-off between device cost, device size, and
accuracy. However, the scanning range of the device limits the variables that can be
estimated from LiDAR data, rendering it unsuitable for use in FRIs until the scanning
range is improved. | en_US |
