SUAS for 3D Tree Surveying: Comparative Experiments on a Closed-Canopy Earthen Dam

Cuizhen Wang,Grayson Morgan,Michael E Hodgson

doi:10.3390/f12060659

Abstract

Defined as “personal remote sensing”, small unmanned aircraft systems (sUAS) have been increasingly utilized for landscape mapping. This study tests a sUAS procedure of 3D tree surveying of a closed-canopy woodland on an earthen dam. Three DJI drones—Mavic Pro, Phantom 4 Pro, and M100/RedEdge-M assembly—were used to collect imagery in six missions in 2019–2020. A canopy height model was built from the sUAS-extracted point cloud and LiDAR bare earth surface. Treetops were delineated in a variable-sized local maxima filter, and tree crowns were outlined via inverted watershed segmentation. The outputs include a tree inventory that contains 238 to 284 trees (location, tree height, crown polygon), varying among missions. The comparative analysis revealed that the M100/RedEdge-M at a higher flight altitude achieved the best performance in tree height measurement (RMSE = 1 m). However, despite lower accuracy, the Phantom 4 Pro is recommended as an optimal drone for operational tree surveying because of its low cost and easy deployment. This study reveals that sUAS have good potential for operational deployment to assess tree overgrowth toward dam remediation solutions. With 3D imaging, sUAS remote sensing can be counted as a reliable, consumer-oriented tool for monitoring our ever-changing environment.

Highlights

Dams provide beneficial functions such as flood control and reliable water supplies in our living environments
The spatial resolution and geocorrection rootmean-square errors (RMSEs) of the orthoimages from the four missions are listed in Table 1 above
This study explored multiple small unmanned aircraft systems (sUAS) missions to test the feasibility and procedure for 3D tree surveying of dense woodland on an earthen dam

Summary

Introduction

Dams provide beneficial functions such as flood control and reliable water supplies in our living environments. As hurricanes and tropical storms on the Atlantic coast are reportedly occurring more frequently in a warmer climate [2,3], earthen dams raise high concerns about their hydraulic stability against severe wind and heavy precipitation during extreme weather events. Dam failures may have monumental repercussions, with dramatic consequences such as loss of life and severe damage to property. The failure of over 70 regulated dams in South Carolina (SC) as a result of back-to-back hurricanes—. Trees growing on dam slopes are one of the more controversial factors contributing to dam failures. In 2000, the Association of State Dam Safety Officials (ASDSO) reported that about 50% of state-regulated dams in 48 U.S states had excessive tree growth [6]

Results

Discussion

Conclusion