571 
polarization 
ig purposes. 
surface are 
lular, multi 
ple air-plant 
vered by the 
rystalline, or 
s (Hall et al. 
on Sorghum 
0.5-1.25 mm 
stalline wax 
rrayed on a 
is (Hull et al. 
letail of plant 
effecting and 
ience (Gates 
af reflectance 
71, Brakkeet 
and specular 
ites from the 
¡omponent is 
inetskii 1966, 
ar reflectance 
;netskii 1966, 
:aves of three 
4, Grant etal. 
ice than matte 
till specularly 
than glabrous 
le presence or 
irious optical 
e exclusively, 
species, forest 
vidual leaves, 
. 1987a, Grant 
vestigated the 
dw the linearly 
! unaffected by 
gth; spectrally, 
ries spectrally 
some evidence 
inswer appears 
gments. These 
eh complica^ 5 
indent constant 
(Figs. 2A and 2B). The denominator contains information about the internal structure of the leaf, in addition to the 
leaf surface, and varies with wavelength as a function of the absorption spectra of the dominant leaf pigments. To 
simplify data interpretation, we prefer to report the polarized reflectance, Rp, rather than the degree of linear 
polarization. 
Wavelength, lint 
Fig. 1. Polarized reflectance, Rq, nonpolarized reflectance, Rn and degree of polarization, P, from the 
adaxial (top) and abaxiaL (bottom) surfaces of leaves of 18 species were measured spectrally at 
approximately the Brewster angle. Data are means of two measurements of six leaves per species. The 
variable Rq in this figure corresponds to Rp in the text. 
The results (Figs. IE and IF) show the degree of linear polarization of a leaf varies spectrally more or less as the 
absorption spectrum of the dominant pigments in the leaf. It is small when Rn( 1) is large, as in the near-infrared 
spectral region, and large when RnO) is small, as in the pigment absorbing visible region. 
Grant concluded that the linear polarization of the light reflected by leaves in the visible and near-infrared wavelengths 
appears to be a first surface phenomena largely unaffected by cellular pigments, metabolites and structure. The light 
reflected by a leaf may be separated into two components with the aid of polarization measurements. One component 
originates at the surface of the leaf and contains no information about leaf pigments, while the other usually emanates 
primarily, but not entirely, from the interior leaf tissue. Its magnitude is determined by leaf pigments, other energy 
absorbing metabolites and leaf structural properties — and possibly in addition by the light scattering and depolarizing 
properties of the leaf surface. 
П.А.4. Other Sources of Polarization. In addition to specular reflection from the amorphous wax substrate, 
the semicrystalline and crystalline wax structures on a leaf surface are potentially capable of polarizing incident light. 
Grant et al. (1993) found evidence for scattering due to surface features on some of the 18 species studied but there was 
no evidence that the light scattered by these small structures was polarized. The explanation may be that Grant et al. 
measured species for which the surface density of small particles is relatively low. They did not measure plants having 
a high density of small surface particles such as, for example, a Colorado blue spruce which exhibits the pronounced 
bluish surface bloom characteristic of small particle scattering. 
II.B. Polarization by Canopies 
II-B.l. Introduction. After correction for the effects of the disturbing atmospheric, data obtained from satellite- 
borne sensors, which measure the ensemble of surfaces - the leaves, stems, and fruits and the litter, soil and rocks - of 
the plant canopy and its environs, potentially include the effects due to three phenomena (1) the light scattering and 
polarizing properties of each scatterer, (2) the architectural arrangement of the scatterers in the canopy, and (3) the