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.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This research was funded by Department of Agriculture and Water Resources, Australian Government as part of its Rural R&D for Profit Program's subproject, titled "Multi-Scale Monitoring Tools for Managing Australian Tree Crops-Industry Meets Innovation", grant number RnD4Profit-14-01-008. The authors acknowledge the Australian Federal Government "Rural R and D for Profit" scheme and Horticulture Innovation Australia for funding this research. The authors appreciate the support, especially during field trips, provided for this research by Chris Searle from MacAvo Consulting, by Simpson Farms Pty. Ltd. (Childers, QLD 4660, Australia), in particular, Chad Simpson, Bundaberg Research Facility, and by the Queensland Government's Department of Agriculture and Fisheries, in particular JohnWilkie and Helen Hofman. We thank Martin Béland for sharing the MATLAB code to calculate the leaf area density, Peter Scarth for MATLAB assistance and Nicholas Goodwin for assisting with data registration. We also thank Aaron Aeberli and Yu-Hsuan Tu for their assistance with fieldwork.