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 satelliteborne
satelliteborne 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
