Spectral absorption features as indicators of water status in coast live oak ( Quercus agrifolia ) leaves

A total of 139 reflectance spectra (between 350 and 2500 nm) from coast live oak ( Quercus agrifolia ) leaves were measured in the laboratory with a spectrometer FieldSpec®Pro FR. Correlation analysis was conducted between absorption features, three-band ratio indices derived from the spectra and corresponding relative water content (RWC, %) of oak leaves. The experimental results indicate that there exist linear relationships between the RWC of oak leaves and absorption feature parameters: wavelength position (WAVE), absorption feature depth (DEP), width (WID) and the multiplication of DEP and WID (AREA) at the 975 nm, 1200 nm and 1750 nm positions and two three-band ratio indices: RATIO 975 and RATIO 1200, derived at 975 nm and 1200 nm. AREA has a higher and more stable correlation with RWC compared to other features. It is worthy of noting that the two three-band ratio indices, RATIO 975 and RATIO 1200, may have potential application in assessing water status in vegetation.