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Robust Single-Image Tree Diameter Estimation with Mobile Phones

Published version
Peer-reviewed

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Abstract

jats:pGround-based forest inventories are reliable methods for forest carbon monitoring, reporting, and verification schemes and the cornerstone of forest ecology research. Recent work using LiDAR-equipped mobile phones to automate parts of the forest inventory process assumes that tree trunks are well-spaced and visually unoccluded, or else require manual intervention or offline processing to identify and measure tree trunks. In this paper, we designed an algorithm that exploits a low-cost smartphone LiDAR sensor to estimate the trunk diameter automatically from a single image in complex and realistic field conditions. We implemented our design and built it into an app on a Huawei P30 Pro smartphone, demonstrating that the algorithm has low enough computational costs to run on this commodity platform in near real-time. We evaluated our app in 3 different forests across 3 seasons and found that in a corpus of 97 sample tree images, our app estimated the trunk diameter with a RMSE of 3.7 cm (R2 = 0.97; 8.0% mean absolute error) compared to manual DBH measurement. It achieved a 100% tree detection rate while reducing the surveyor time by up to a factor of 4.6. Our work contributes to the search for a low-cost, low-expertise alternative to terrestrial laser scanning that is nonetheless robust and efficient enough to compete with manual methods. We highlight the challenges that low-end mobile depth scanners face in occluded conditions and offer a lightweight, fully automatic approach for segmenting depth images and estimating the trunk diameter despite these challenges. Our approach lowers the barriers to in situ forest measurements outside of an urban or plantation context, maintaining a tree detection and accuracy rate comparable to previous mobile phone methods even in complex forest conditions.</jats:p>

Description

Peer reviewed: True


Funder: David Cheriton Graduate Scholarship


Funder: Canadian National Research Council


Funder: Harding Distinguished Postgraduate Scholarship

Keywords

forest inventory, forest carbon estimation, diameter at breast height (DBH), mobile phone, LiDAR, time-of-flight

Journal Title

Remote Sensing

Conference Name

Journal ISSN

2072-4292
2072-4292

Volume Title

Publisher

MDPI AG
Sponsorship
Harding Distinguished Postgraduate Scholarship Canadian National Research Council David Cheriton Graduate Scholarship
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