Novel vegetation index for chlorophyll non-destructive spectral analysis

Directional reflectance spectra from 400 to 780 nm were acquired at an angle-of-view of 30° for nadir illuminated leaves of four different kinds of plants (Codiaeum variegatum, Eleagnus angustifolia, Pittosporum tobira, Ficus benjamini). We found that, differently from hemispherical reflectance measurements, directional reflectance data do not correlate well with chlorophyll content. This is mainly due to the Fresnel reflections at the air-epidermis and epidermis-inner layer interfaces that gives the main contribute to the reflectance in 400-480 nm band, where chlorophyll absorption is maximum. The inner reflectance (RI), obtained by subtracting the outer reflectance from the measured spectra, was found to correlate to chlorophyll content. A good correlation (r2 = 0.98) of RI(?)/R750 I versus the log(Chl) was obtained for RI(?) in the reflectance maximum in the green band around 550 nm. The error in the determination of Chl content was of about 3.5 ?g/cm2, lower than that obtained by applying previously suggested vegetation indexes to our experimental data.