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The use of remote sensing for scene composition analysis and stress detection in plants

Cannon, Mark P. (1982) The use of remote sensing for scene composition analysis and stress detection in plants. Masters by Research thesis, Murdoch University.

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The jarrah forest of South West Western Australia is degrading due to the presence of a root-rot disease caused by the fungal pathogen Phytophthora cinncanomi Rands.

The dominant species of the forest, Eucalyptus marginata Sm., takes many years to die from this disease, but plant species of the understorey show symptoms and die within a few weeks. Accordingly, Banksia grandis Willd., an understorey species and indicator of the presence of the disease, was chosen to determine if previsual stress detection could be achieved using remote sensing techniques.

In this investigation, spectroradiometry was used in conjunction with selective photography to establish in what regions of the spectrum the greatest changes in reflectance occur. The two approaches, spectroradiometry and photography, are seen as complementary in the interpretation process.

Stress detection relies on a knowledge of the spectral signature of healthy plants of the species being investigated. The spectral signature depends upon the scene being viewed and the configuration of the particular radiometer being used. Hence scene composition analysis is a preliminary step in spectral signature determination.

Various scenes across the canopy of a Banksia grandis tree were analysed and produced a range of signals. Disorders in the chosen species were detected by radiometric techniques as well as by visual and densitometric analysis of the photography. Changes in the visible reflectance of the plant were found to be greater than changes in the near-infrared reflectance. Changes in the near-infrared reflectance did not occur before changes in the visible or were too subtle to be identified due to the "noise" in the signal.

Thermal radiometry was also employed for stress detection but again the changes in canopy temperature compared to changes in visible reflectance were subtle in the early stages of stress and difficult to recognise due to the variation in the temperature across the banksia canopy.

Oblique aerial photography has advantages over vertical aerial photography in ease of interpretation and in terms of cost and availability and shows promise as a remote sensing tool for environmental monitoring.

Colour infrared photography used in other studies has proved advantageous over normal colour photography particularly for stress detection. Its application for this purpose in Australian sclerophyll forest however, appears doubtful from the point of view of spectral sensitivity and visual interpretability.

Item Type: Thesis (Masters by Research)
Murdoch Affiliation(s): School of Environmental and Life Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): O'Connor, Des
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