A Comparison of the Performances of Unmanned-Aerial-Vehicle (UAV) and Terrestrial Laser Scanning for Forest Plot Canopy Cover Estimation in Pinus massoniana Forests

Wenxia Dai,Zhen Dong,Shangshu Cai,Qingfeng Guan,Qing Liu,Ruibo Chen,Chao Chen,Rundong Liu

doi:10.3390/rs14051188

Abstract

Canopy cover is an important indicator and commonly used in forest management applications. Unmanned-Aerial-Vehicle (UAV)—Borne Laser Scanning (ULS) has drawn increasing attention as a new alternative source for forest field inventory due to its spatial resolution comparable to that of Terrestrial Laser Scanning (TLS). In this study, the performance of plot canopy cover estimations from ULS and TLS is investigated. The experiment was conducted in 16 plots from two Pinus massoniana forests with different stand conditions in Guangxi, China. Both the Canopy Height Model (CHM)-based and Individual Tree Delineation (ITD)-based methods were used to estimate the canopy cover. The influence of CHM pixel sizes on the estimations was also analyzed. Our results demonstrated that the accuracies of ULS (R2: 0.992–0.996, RMSE: 0.591–0.820%) were better than those of TLS (R2: 0.541–0.846, RMSE: 3.642–6.297%) when compared against the reference. The average difference between the ULS and TLS estimations was 6.91%, and the disagreement increased as the forest complexity increased. The reasonable CHM pixel sizes for the canopy cover estimations were 0.07–1.2 m for ULS and 0.07–1.5 m for TLS. This study can provide useful information for the selection of data sources and estimation methods in plot canopy cover mapping.

Highlights

Forest canopy cover, which is defined as the proportion of the forest floor covered by the vertical projection of tree crowns [1,2], is directly related to the forest floor microclimate and light conditions [3–5] and is commonly used for biophysical and natural resource management applications
The ULS_CHM method showed the is the mean of the reference canopy cover, and n is the number of plots
In the Canopy Height Model (CHM) method, our results demonstrated that the UAV laser scanning (ULS) estimations were larger produced slight overestimation of canopy cover and underestimated the canopy than the Terrestrial Laser Scanning (TLS) estimations for all the plots

Summary

Introduction

Forest canopy cover, which is defined as the proportion of the forest floor covered by the vertical projection of tree crowns [1,2], is directly related to the forest floor microclimate and light conditions [3–5] and is commonly used for biophysical and natural resource management applications. The spatially accurate mapping of canopy cover plays a critical role in forest stand structure classification [6], biomass production [7], wildfire behavior simulation [8], and wildlife habitat assessment [9,10]. Canopy cover has been obtained from field measurements using sighting tubes [11], line intersect sampling [12], canopy photography [13], and the portable station field-map [14], which are laborious and time consuming. The field measurements obtained via these methods may be inaccurate because the crown boundaries can Remote Sens. Remote sensing techniques can provide spatially continuous observations with a higher efficiency and at a lower cost. Light detection and ranging (LiDAR) is a promising tool for quantifying forest structural parameters because of its ability to assess 3D information with high precision [15–17]. LiDAR has the potential to replace field measurements or even be used to assess the quality of field measurements [5,18,19]

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