Inter-comparison of remote sensing platforms for height estimation of mango and avocado tree crowns

Measuring canopy structure for horticulture tree crops using remote sensing datasets

“…The absolute height difference between these two datasets was 0.07 m -0.58 m. ALS may underestimate canopy height due to the lower point density and the larger footprint size in relation to canopy structure (Wu et al, 2020). To derive the maximum canopy height from ALS data, a laser beam has to hit the tree apex and the return of this laser beam has to be recorded by the scanner (Wu et al, 2020). Data acquisition parameters such as flying altitude and pulse density can affect the ability of height estimation from ALS data (Yu et al, 2012).…”

“…respectively, based on a calculation by the data provider of 120 ground control points. (Wu et al, 2018, Wu et al, 2020. To…”

“…There is a significant opportunity and costbenefit for developing and adopting precision horticultural practices that can optimize production whilst minimising input costs (Zude-Sasse et al, 2016). Remote sensing can play an important role in precision agriculture, enabling measurement, mapping, monitoring and modelling of fruit/crops, individual trees, orchard blocks and larger areas (Liaghat and Balasundram, 2010, Robson et al, 2017a, Wu et al, 2018, Wu et al, 2020. Technologies such as satellite, airborne, unoccupied aerial vehicle (UAV) and proximal sensors have seen a rapid growth in availability and subsequent evaluation of horticultural farms , Díaz-Varela et al, 2015, Calderón et al, 2013, Elsayed et al, 2016.…”

“…UAV based imagery have also been used in recent years for tree counting, canopy height, crown area and canopy volume for olive trees (Torres-Sánchez et al, 2014, Salamí et al, 2019. Although UAV RGB and multispectral imagery have achieved high accuracy, their coverage area is limited to 1-10 km 2 (depending on flying height, speed and types of platform) due to battery life and line-of-sight regulations (Johansen et al, 2018, Wu et al, 2020. Airborne, especially satellite stereo imagery, have been used widely in forestry (Persson and Perko, 2016, Straub et al, 2013, Yu et al, 2015, but are rarely used for mapping the canopy structure of horticultural tree crops.…”

“…The maximum canopy height of the avocado, macadamia and mango trees was calculated by extracting the value of the highest point within each tree crown for both the ALS and TLS data and subtracting the ground elevation from this height measurement. The absolute height difference between these two datasets was 0.07 m -0.58 m. ALS may underestimate canopy height due to the lower point density and the larger footprint size in relation to canopy structure (Wu et al, 2020). To derive the maximum canopy height from ALS data, a laser beam has to hit the tree apex and the return of this laser beam has to be recorded by the scanner (Wu et al, 2020).…”