New vegetation indices for remote measurement of chlorophylls based on leaf directional reflectance spectra.

Directional reflectance (R) spectra from 380 to 780 nm for nadir illuminated leaves of four different plants (croton, Codiaeum variegatum; spotted eleagnus, Eleagnus pungens Maculata; Japanese pittosporum, Pittosporum tobira and Benjamin fig, Ficus benjamina Starlight) were acquired at a viewing angle of 30 degrees from the nadir direction. Chlorophyll-a and -b content of leaves covered a range of 1-60 and 0.5-21 microg/cm(2), respectively. In contrast with previous results from hemispherical reflectance measurements, directional reflectance data does not correlate well with chlorophyll concentration. This is mainly due to the external reflectance (R(E)) at the leaf epidermis, caused by the mismatch of the refractive index at the air-epidermis and epidermis-inner layer boundary. The external reflectance can be identified with the blue flat reflectance between 380 and 480 nm. The inner reflectance (R(I)), obtained by subtracting the external reflectance from the measured spectra, was found to be linearly related to the logarithm of the chlorophyll content. Good fitting of the log (Chl) versus R(I)(lambda) curves were obtained for R(I) in the green band (around 550 nm) and close to the inflection point in the red edge (around 700 nm). The coefficient of determination, r(2), of curve fitting improved (up to 0.97) when the normalised inner reflectance NR(I)(lambda)=R(I)(lambda)/R(I)(lambda(0)), with lambda(0)>or=750 nm, was used instead of the absolute reflectance. The best indices for Chl, Chl-a and Chl-b determination were R(I)(542)/R(I)(750), R(I)(706)/R(I)(750) and R(I)(556)/R(I)(750), respectively. However, since the content of Chl-a relative to Chl-b was almost constant for the plants investigated, the two last indices must be further validated on leaves with a high variability in the Chl-a:Chl-b ratio. The error in the determination of chlorophyll content was found to be of the order of 10%. This value was lower than those obtained by applying the vegetation indices previously suggested. Therefore, the normalised inner reflectance in the green and in the red edge represents a more suitable index for the chlorophyll determination than those up to now used.

[1]  W. Verhoef.  Light scattering by leaf layers with application to canopy reflectance modelling: The SAIL model , 1984 .

[2]  H. Gausman,et al.  Refractive index of plant cell walls. , 1974, Applied optics.

[3]  S. Jacquemoud.  Inversion of the PROSPECT + SAIL Canopy Reflectance Model from AVIRIS Equivalent Spectra: Theoretical Study , 1993 .

[4]  A. Gitelson,et al.  Use of a green channel in remote sensing of global vegetation from EOS- MODIS , 1996 .

[5]  Leonid Fukshansky,et al.  ON THE INTERPRETATION OF ABSORPTION SPECTRA OF LEAVES–II. THE NON‐ABSORBED RAY OF THE SIEVE EFFECT and THE MEAN OPTICAL PATHLENGTH IN THE REMAINDER OF THE LEAF , 1990 .

[6]  Moon S. Kim,et al.  Ratio analysis of reflectance spectra (RARS): An algorithm for the remote estimation of the concentrations of chlorophyll A, chlorophyll B, and carotenoids in soybean leaves , 1992 .

[7]  Leonid Fukshansky,et al.  ON THE INTERPRETATION OF ABSORPTION SPECTRA OF LEAVES–I. INTRODUCTION and THE CORRECTION OF LEAF SPECTRA FOR SURFACE REFLECTION , 1990 .

[8]  P. Curran,et al.  Technical Note Grass chlorophyll and the reflectance red edge , 1996 .

[9]  W. R. Windham,et al.  Exploring the relationship between reflectance red edge and chlorophyll concentration in slash pine leaves. , 1995, Tree physiology.

[10]  A. Gitelson,et al.  Detection of Red Edge Position and Chlorophyll Content by Reflectance Measurements Near 700 nm , 1996 .

[11]  A. Gitelson,et al.  Non-destructive determination of chlorophyll content of leaves of a green and an aurea mutant of tobacco by reflectance measurements , 1996 .

[12]  Claus Buschmann,et al.  In vivo spectroscopy and internal optics of leaves as basis for remote sensing of vegetation , 1993 .

[13]  B. Datt,et al.  Visible/near infrared reflectance and chlorophyll content in Eucalyptus leaves , 1999 .

[14]  D. Horler,et al.  The red edge of plant leaf reflectance , 1983 .

[15]  Giovanni Agati,et al.  Remote measurement of dark-green canopy chlorophyll concentration by directional reflectance spectra , 2001, SPIE Remote Sensing.

[16]  A. Gitelson,et al.  Signature Analysis of Leaf Reflectance Spectra: Algorithm Development for Remote Sensing of Chlorophyll , 1996 .

[17]  A. Gitelson,et al.  Plant Stress Detection by Reflectance and Fluorescence a , 1998 .

[18]  Paul J. Curran,et al.  The relationship between red edge and chlorophyll concentration in the Broadbalk winter wheat experiment at Rothamsted , 1994 .

[19]  H. Lichtenthaler.  CHLOROPHYLL AND CAROTENOIDS: PIGMENTS OF PHOTOSYNTHETIC BIOMEMBRANES , 1987 .

[20]  B. Pinty,et al.  A physical model of the bidirectional reflectance of vegetation canopies , 1990 .

[21]  R. Moran.  Formulae for determination of chlorophyllous pigments extracted with n,n-dimethylformamide. , 1982, Plant physiology.

[22]  Bruce R. Kowalski,et al.  Piece-Wise Multiplicative Scatter Correction Applied to Near-Infrared Diffuse Transmittance Data from Meat Products , 1993 .