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 (R 2 = 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.

This research investigates the capability of field-based spectroscopy (350–2500 nm) for discriminating banana plants (Cavendish subgroup Williams) infested with spider mites from those unaffected. Spider mites are considered a major threat to agricultural production, as they occur on over 1000 plant species, including banana plant varieties. Plants were grown under a controlled glasshouse environment to remove any influence other than the imposed treatment (presence or absence of spider mites). The spectroradiometer measurements were undertaken with a leaf clip over three infestation events. From the resultant spectral data, various classification models were evaluated including partial least squares discriminant analysis (PLSDA), K-nearest neighbour, support vector machines and back propagation neural network. Wavelengths found to have a significant response to the presence of spider mites were extracted using competitive adaptive reweighted sampling (CARS), sub-window permutation analysis (SPA) and random frog (RF) and benchmarked using the classification models. CARS and SPA provided high detection success (86% prediction accuracy), with the wavelengths found to be significant corresponding with the red edge and near-infrared portions of the spectrum. As there is limited access to operational commercial hyperspectral imaging and additional complexity, a multispectral camera (Sequoia) was assessed for detecting spider mite impacts on banana plants. Simulated multispectral bands were able to provide a high level of detection accuracy (prediction accuracy of 82%) based on a PLSDA model, with the near-infrared band being most important, followed by the red edge, green and red bands. Multispectral vegetation indices were trialled using a simple threshold-based classification method using the green normalised difference vegetation index (GNDVI), which achieved 82% accuracy. This investigation determined that remote sensing approaches can provide an accurate method of detecting mite infestations, with multispectral sensors having the potential to provide a more commercially accessible means of detecting outbreaks.

UAS-based multi-spectral imagery is becoming ubiquitous for monitoring and managing various horticultural crops. To accurately measure and monitor their structure and condition and estimate yields, appropriately corrected data must be used to drive the necessary algorithms. There are several popular radiometric correction methods commonly used for UAS-based data correction. However, their relative and absolute accuracies are not known. This study used three flight datasets, including along- and across-tree-row flight patterns in an avocado orchard. Four correction methods were applied to produce at-surface reflectance image mosaics for each flight pattern as well as the grid pattern and the results were compared to assess the reflectance consistency. Results show that no method provided consistently correct at-surface reflectance for the same features. A BRDF correction workflow was being developed to address these limitations. Preliminary application of the BRDF correction shows that it significantly improves the brightness consistency of features across different images.

Australia is one of the world's largest producers of macadamia nuts. As macadamia trees can take up to 15 years to mature and produce maximum yield, it is important to optimize tree condition. Field based assessment of macadamia tree condition is time-consuming and often inconsistent. Using remotely sensed imagery may allow for faster, more extensive, and more consistent assessment of macadamia tree condition. To identify individual macadamia tree crowns, high spatial resolution imagery is required. Hence, the objective of this work was to develop and test an approach to map the condition of individual macadamia tree crowns using both multi-spectral Unmanned Aerial Vehicle (UAV) and WorldView-3 imagery for different macadamia varieties and three different sites located near Bundaberg, Australia. A random forest classifier, based on all available spectral bands and selected vegetation indices was used to predict five condition categories, ranging from excellent (category 1) to poor (category 5). Various combinations of the developed models were tested between the three sites and over time. The results showed that the multi-spectral WorldView-3 imagery produced the lowest out of bag (OOB) classification errors in most cases. However, for both the UAV and the WorldView-3 imagery, more than 98.5% of predicted macadamia condition categories were either correctly mapped or offset by a single category out of the five condition categories (excellent, good, moderate, fair and poor) for trees of the same variety and at one point in time. Multi-temporally, the WorldView-3 imagery performed better than the UAV data for predicting the condition of the same macadamia tree variety. Applying a model from one site to another site with the same macadamia tree variety produced OOB classification between 31.20 and 42.74%, but with >98.63% of trees predicted within a single condition category. Importantly, models trained based on one type of macadamia tree variety could not be successfully applied to a site with another variety. The developed classification models may be used as a decision and management support tool for the macadamia industry to inform management practices and improve on-demand irrigation, fertilization, and pest inspection at the individual tree level.

Bananas are the fourth most important staple food source globally and are considered vital for economic development and food security in many countries. Current management of commercial banana crops is largely based on in-field visual appraisal and manual record keeping, with targeted agronomic activities guided by the manual tagging of individual plants in the field. Such activities can be labour-intensive, subjective and lacking rigour as they often rely on the experience of the individual undertaking the assessment. Remote sensing technologies play a fundamental, enabling role in precision agriculture and are becoming increasingly commonplace. Applications such as the monitoring of crop phenology to guide management activities, determining harvest readiness, pest and disease detection and yield forecasting using remote sensing have been adopted by other industries, but for banana these tasks are still currently undertaken manually. Little to no adoption of remote sensing applications exist in the banana industry and research into new applications is minimal. The low level of adoption is largely due to the unique phenology, morphology, propagation, and growing properties of banana plants that limit the use of whole-field remote sensing applications common in other crops. To address these knowledge gaps, this thesis developed methods and investigated the accuracies of ground and unoccupied aerial vehicle (UAV) based sensors for measuring several key needs of the Australian banana industry.

Robust spatio-temporal detection and delineation methods were developed and assessed for their ability to accurately represent individual banana plant crowns from UAV multispectral imagery. Furthering this concept of individual plant monitoring, a time series based on a 15-month UAV flight campaign was used to create and compare spectral and morphological data of individual plants over time, from initial establishment to harvest. Verification against infield measurements determined that UAV-based multi-temporal crop monitoring models of individual banana plants can be used for the determination of key phenological growth stages of banana plants (including establishment, flower emergence and harvest) and offer pre-harvest yield forecasts. Finally, the accuracies of both hyperspectral and multispectral data for measuring mite infestations on banana plants were investigated, with both sensors providing promising results. Overall, this research's findings and developed methods contribute important information that enhances crop knowledge and understanding. The methods presented have the potential to add novel precision agriculture applications to the banana industry that compensate for the unique growth and propagation of banana crops. These outcomes have the potential to improve and promote economic advancement and food security in the banana industry.