UAV multispectral imagery and satellite data can be used to monitor physiological stress in trees.
Researchers from Crown research institute Scion treated selected Pinus radiata with herbicide to stress the trees. The colour of the pine needles changed as the herbicide took effect. The changes were monitored over time using a UAV-mounted multispectral camera, and using data collected from the Rapid Eye satellite.
Lead researcher Jonathan Dash says both data sources were sensitive enough to detect the changes in needle colour. “However, the UAV data were more sensitive at a finer spatial resolution and could detect stress down to the level of individual trees. The satellite data we tested could only detect stress in clusters of four or more trees.”
Resampling the UAV imagery to the same spatial resolution as the satellite imagery showed the differences in sensitivity were not just the result of spatial resolution. Vegetation indices suited to the sensor characteristics of each platform were needed to optimise the detection of physiological stress from each data source.
“Detecting physiological stress in forest trees is vital for ensuring productive forest systems,” says Jonathan.
“We have shown that remote sensing can be used to detect conditions that cause changes in foliage colour before they can be observed from the ground. UAV imagery was more sensitive, but satellite data remains a very valuable and cost-effective way to observe trends in forest health over larger areas. Research like this provides a useful range of complimentary tools for forest growers and researchers to monitor forests”
Forest owners and managers can now use remotely-sensed data opportunities to augment traditional monitoring practices. This will be especially useful in distant and difficult to access terrain. As well as physiological stress caused by disease, the effects of drought, lack of soil nutrients and attacks by pests will be able to be detected and responded to early, leading to healthier and more productive forests.
Photo: Linking multispectral satellite imagery to UAV data provides a valuable tool for monitoring forest health
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