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Many factors affect light reflectance of leaves (Bowden, 1974): 
structure, maturation, phyllotaxis, pigments, damage, pubescence, 
water content, senescence, and many stresses (like soil salinity 
and nutrient deficiencies and toxicities). 
The spectral reflectance, absorptance and transmittance and the 
geometric and optical parameters (void-area index, index of re- 
fraction, scattering coefficient, absorption coefficient, and 
infinite reflectance) have been determined for 11 plant genera 
(Gausman et al., 1970) and 20 crop plants (Gausman et al., 1973d). 
Optical parameters have been determined for leaves of 30 plant 
species (Gausman and Allen, 1973c). 
Allen et al., (1969) used a rough plane-parallel model to explain 
the interaction of diffuse light with a compact mature leaf, like 
corn, or immature leaves of plants that develop intercellular 
air spaces at maturity. The model is specified by two optical 
constants - an effective index of refraction, n, and an effective 
coefficient of absorption, k. It yields a third parameter D, the 
equivalent thickness of pure water needed to produce the observed 
leaf absorption. 
Tucker and Garratt (1977) developed a stochastic leaf radiation 
model to explain the interaction of diffuse light with a dicot 
leaf. Results of this approach agreed with those of Gausman et 
al. (1974b) and Allen et al. (1969). 
The spectral reflectance of green vegetation against a soil back- 
ground decreases in regions of absorption and increases in regions 
of minimal or no absorption as the vegetational density increases 
until a stable or unchanging spectral reflectance, called infinite 
(asymptotic) spectral reflectance, is reached (Allen and Richardson, 
1968). In the visible and in the 1.5- to 2.5um waveband, infinite 
reflectance (R ) is reached as the plants reach a leaf area index 
(LAI) of 2; LAI is the cumulative one-sided leaf area per unit 
ground area measured from the canopy top to a plane at a given 
distance aboveground. 
In the 0.75- to 1.35-um waveband, an LAI of about 8 is needed to 
reach R because of the transparency of the leaves (Allen et al., 
1969). Tucker (1977a) has corrobated these earlier findings for 
green grass canopies. 
Infinite reflectance can be calculated if the reflectance and 
transmittance of a single leaf is known and is a parameter that 
can be used for discrimination between vegetation categories 
(Richardson et al., 1969). 
Instrumentation and General Procedures 
A Beckman^ Model DK-2A spectrophotometer, equipped with a reflec- 
  
2) Mention of a company name or trademark is for the readers bene- 
fit and does not constitute endorsement of a particular product 
by the U.S.Department of Agriculture over others that may be 
commercially available.