Suitability of Airborne and Terrestrial Laser Scanning for Mapping Tree Crop Structural Metrics for Improved Orchard Management

Abstract

Airborne Laser Scanning (ALS) and Terrestrial Laser Scanning (TLS) systems are useful tools for deriving horticultural tree structure estimates. However, there are limited studies to guide growers and agronomists on different applications of the two technologies for horticultural tree crops, despite the importance of measuring tree structure for pruning practices, yield forecasting, tree condition assessment, irrigation and fertilization optimization. Here, we evaluated ALS data against near coincident TLS data in avocado, macadamia and mango orchards to demonstrate and assess their accuracies and potential application for mapping crown area, fractional cover, maximum crown height, and crown volume. ALS and TLS measurements were similar for crown area, fractional cover and maximum crown height (coefficient of determination (R2) ≥ 0.94, relative root mean square error (rRMSE) ≤ 4.47%). Due to the limited ability of ALS data to measure lower branches and within crown structure, crown volume estimates from ALS and TLS data were less correlated (R2 = 0.81, rRMSE = 42.66%) with the ALS data found to consistently underestimate crown volume. To illustrate the effects of different spatial resolution, capacity and coverage of ALS and TLS data, we also calculated leaf area, leaf area density and vertical leaf area profile from the TLS data, while canopy height, tree row dimensions and tree counts) at the orchard level were calculated from ALS data. Our results showed that ALS data have the ability to accurately measure horticultural crown structural parameters, which mainly rely on top of crown information, and measurements of hedgerow width, length and tree counts at the orchard scale is also achievable. While the use of TLS data to map crown structure can only cover a limited number of trees, the assessment of all crown strata is achievable, allowing measurements of crown volume, leaf area density and vertical leaf area profile to be derived for individual trees. This study provides information for growers and horticultural industries on the capacities and achievable mapping accuracies of standard ALS data for calculating crown structural attributes of horticultural tree crops.

Seamless integration of above- and under-canopy unmanned aerial vehicle laser scanning for forest investigation

“…Existing solutions for improving the completeness of data can be divided into two groups: the first is to densify the data collection such as to add multiple viewing angles of scanner in order to enhance canopy and stem completeness, e.g., (Roşca et al 2018;Wu et al 2020), or to densify trajectories in order to record more trees from more viewing perspectives, e.g., (Morsdorf et al 2017;Del Perugia et al 2019;Kuželka et al 2020); The second is the fusion of datasets from different platforms, especially between terrestrial and aerial platforms, e.g., (Paris et al 2017;Giannetti et al 2018;Dai et al 2019;Pyörälä et al 2019).…”

Canopy Parameter Estimation of Citrus grandis var. Longanyou Based on LiDAR 3D Point Clouds

“…The value of V VB falls within the mid-range for volume measurement, but it also required the longest run time (T VB = 4.867s) which fluctuated greatly. Therefore, the VB algorithm could be selected to calculate canopy volume off-line, and to precisely measure relevant parameters of leaves, such as leaf area and LAD [39,59]. The AS algorithm can better express the actual shape of the actual canopy.…”

Phenotyping Architecture Traits of Tree Species Using Remote Sensing Techniques

“…In addition, traits such as crown density and structural complexity were found to be associated with the genetic diversity within and between species. Wu et al (2020a) evaluated the ability of ALS and TLS data to assess the crown structure traits of individual fruit trees, including avocado trees, macadamia trees, and mango trees. Their study showed that ALS and TLS both provided similar crown area, fractional cover, and maximum crown height (R 2  0.94, relative RMSE  4.47%), while the crown volume estimations were less correlated (R 2 = 0.81, relative RMSE = 42.66%), with the ALS approach underestimating such data compared to the TLS data, primarily due to the limited capacity of ALS data to measure lower branches and the within-canopy structure.…”

“…In addition, canopy height from reconstructed 3D shape models is used to evaluate crop water status for irrigation planning. It can also be used as a guideline for sprayer settings to achieve a suitable spray volume and timing and as a variable to set the operation of harvesting machines and for pruning tasks in tree fruit orchards (Zhang et al, 2018;Aboutalebi et al, 2020;Pereira et al, 2020;Wu et al, 2020aWu et al, , 2020b.…”

“…Other essential canopy traits that can be measured using 3D models include area, volume, and density. These traits can be directly associated with precision agriculture and assist in increasing crop management efficiency, such as pruning, harvesting, fertilizer and pesticide applications, and monitoring of breeding trials (Colaço et al, 2017;Patrick and Li, 2017;Torres-Sánchez et al, 2018;Caruso et al, 2019;Yan et al, 2019;Wu et al, 2020a;Zhu et al, 2020). Using the triangulation principle for generating point clouds, the stereo vision technique RGB-D has been used to measure canopy volume in tree fruits.…”