Remote Sensing of Chlorophyll a, Chlorophyll b, Chlorophyll a+ b, and Total Carotenoid Content in Eucalyptus Leaves

Abstract

Algorithms based on reflectance band ratios have been developed for the remote estimation of chlorophyll a, chlorophyll b, chlorophyll a+b, and total carotenoid content of Eucalyptus leaves. Reflectance spectra over the 400–2500 nm range with a spectral resolution of 2 nm and the content of chlorophylls a, b, a+b, and total carotenoids were determined for leaves from several Eucalyptus species covering a wide range of chlorophyll a content (0.0121–0.0435 mg/cm 2). Maximum sensitivity of reflectance to variation in pigment content was found in the green wavelength region at 550 nm and at 708 nm in the far-red wavelengths. The reflectance in the main pigment absorption regions in the blue (400–500 nm) and red (660–690 nm) wavelengths proved to be insensitive to variation in pigment content. The ratio R672/( R550× R708) correlated best with chlorophyll a, chlorophyll a+b, and total carotenoid contents. The ratio R672/ R550 correlated best with chlorophyll b content. Reflectance ratios involving near infrared bands such as R750/ R550 and R750/ R700 did not correlate well with pigment content. This was due to the differential scattering effects of the wide range of young and mature leaf samples. A method was developed for adjusting all spectra to the same level of scatter. The near-infrared-based reflectance ratios from the scatter adjusted spectra showed high sensitivity to pigment content. The ratio R860/( R550 ×R708) from the scatter adjusted spectra correlated best with chlorophyll a, chlorophyll a+b, and total carotenoid contents, while R860/ R550 correlated best with chlorophyll b content. The newly developed algorithms were tested on a validation data set and allowed accurate estimates of leaf pigment content. The pigment contents estimated by the ratios from untransformed spectra, R672/( R550 ×R708) and R672/ R550, were found to be not significantly different from the estimates obtained using the scatter-adjusted reflectance ratios, R860/( R550 ×R708) and R860/ R550.