Remote sensing of chlorophyll a, chlorophyll b, chlorophyll a+b, and total carotenoid content in eucalyptus leaves

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 nn and at 708 nun 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/(R550XR708) 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/(R550XR708) 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/(R550XR708) and R672/R550, were found to be not significantly different from the estimates obtained using the scatter-adjusted reflectance ratios, R860/(R550XR708) and R860/R550. (C) Elsevier Science Inc., 1998.