Assessing eucalypt foliar health with field-based spectra and high spatial resolution hyperspectral imagery

Advances in remote sensing technologies, especially the increasing application of hyperspectral datasets, provide new opportunities to develop reliable, robust indicators of canopy health for Australian eucalypt forests. Leaf reflectance in the visible and near-infrared wavelengths measured using a hand-held spectroradiometer were compared with foliar damage, leaf morphology, chlorophyll fluorescence and chlorophyll content sampled from eucalypt leaves exhibiting symptoms of canopy dieback. Compact Airborne Spectrographic Imager (CASI-2) imagery was also collected over the crowns and spectral signatures extracted from the 80 cm spatial resolution imagery. Results indicate that a number of spectroradiometer derived indices were significantly correlated with leaf variables. These indices were predominantly those that incorporated the spectral red-edge such as changes in slope, the slope of the lower red-edge, the maximum slope, the inflection wavelength and newly proposed red/green indices which specifically target anthocyanins. Mean leaf chlorophyll content, leaf chlorophyll fluorescence, leaf length to width ratio, and estimated percent leaf with red discoloration were all highly significantly correlated to several CASI-2 derived indices. Overall the research has demonstrated strong relationships between eucalypt leaf spectra and leaf damage and morphometry variables