Volume 43, 2015, Pages 55-83
a
U.S Geological Survey (USGS), Denver Federal Center, MS 973 Box 25046, Denver, CO, United States
b Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, P.O. Box 217, Enschede, Netherlands
b Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, P.O. Box 217, Enschede, Netherlands
Abstract
Past laboratory and
field studies have quantified phenolic substances in vegetative matter
from reflectance measurements for understanding plant response to
herbivores and insect predation. Past remote sensing studies on
phenolics have evaluated crop quality and vegetation patterns caused by
bedrock geology and associated variations in soil geochemistry. We
examined spectra of pure phenolic compounds, common plant biochemical
constituents, dry leaves, fresh leaves, and plant canopies for direct
evidence of absorption features attributable to plant phenolics. Using
spectral feature analysis with continuum removal, we observed that a
narrow feature at 1.66 μm is persistent in spectra of manzanita, sumac,
red maple, sugar maple, tea, and other species. This feature was
consistent with absorption caused by aromatic C H bonds in the chemical
structure of phenolic compounds and non-hydroxylated aromatics. Because
of overlapping absorption by water, the feature was weaker in fresh leaf
and canopy spectra compared to dry leaf measurements. Simple linear
regressions of feature depth and feature area with polyphenol
concentration in tea resulted in high correlations and low errors (%
phenol by dry weight) at the dry leaf(r2 = 0.95, RMSE = 1.0%, n = 56), fresh leaf(r2 = 0.79, RMSE = 2.1%, n = 56), and canopy (r2
= 0.78, RMSE = 1.0%, n = 13) levels of measurement. Spectra of leaves,
needles, and canopies of big sagebrush and evergreens exhibited a weak
absorption feature centered near 1.63 μm, short ward of the phenolic
compounds, possibly consistent with terpenes. This study demonstrates
that subtle variation in vegetation spectra in the shortwave infrared
can directly indicate biochemical constituents and be used to quantify
them. Phenolics are of lesser abundance compared to the major plant
constituents but, nonetheless, have important plant functions and
ecological significance. Additional research is needed to advance our
understanding of the spectral influences of plant phenolics and terpenes
relative to dominant leaf biochemistry (water, chlorophyll,
protein/nitrogen, cellulose, and lignin). © 2015 Elsevier B.V.
Author keywords
Canopy chemistry; Continuum removal; Polyphenols; Remote sensing; Spectral feature analysis; Spectroscopy; Tannin
Indexed keywords
Species Index: Acer rubrum; Acer saccharum; Arctostaphylos; Artemisia tridentata; Hexapoda; Rhus
