Mapping the condition of macadamia tree crops using multi-spectral UAV and WorldView-3 imagery
byk. Johansen, Q. Duan, Yu-HsuanTu, C. Searle, D. Wu, S. Phinn, A. Robson, M.F. McCabe
Year:2020DOI:10.1016/j.isprsjprs.2020.04.017
Extra Information
ISPRS Journal of Photogrammetry and Remote Sensing, Volume 165, pp. 28-40, (2020)
Abstract
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.