PE&RS January 2016 - page 52

own-rooted: they are not grafted. In 2013 the research vine-
yard containing these two species was established at the MBG,
Saint Louis, Missouri. The vineyard includes multiple clones
of each of four genotypes V. riparia genotypes and multiple
clones of each of five V. rupestris genotypes. This experi-
mental design presents an important opportunity to compare
spectral signatures among and within species growing under
common conditions.
Remote sensing can be used to map and monitor spatio-
temporal dynamics of crops and different vegetation com-
munities provided that different species are spectrally
distinct within the landscape. Spectral signatures of plants
are expressions of canopy biochemical and structural proper-
ties including leaf area index (LAI ), leaf/canopy water con-
tent, chlorophyll concentration, leaf internal structure, leaf
angle orientation and specific leaf area (SLA , leaf area per unit
mass). It has been suggested that plants may show similar
spectral profiles because they are composed of the same spec-
trally active materials, e.g., pigments, water, cellulose, etc.
(Baret et al., 1987; Jacquemoud and Baret, 1990). Under com-
mon conditions, how do the spectral signatures of distinct
species, and distinct genotypes within species, differ from
one another? Understanding the spectral bands significant for
discrimination of genotypes and species are always promising
and critical in remote sensing based monitoring of crop health
(Burkholder et al., 2011; Cho et al., 2008).
Leaf chemical properties are principal determinants of
plant physiology and biogeochemical processes in terres-
trial ecosystems (Hedin, 2004; Wang et al., 2010). Numerous
studies show that empirical relationships exist between leaf
spectral properties and leaf morphological and physiological
conditions (Adams et al., 1993; Adams et al., 2000; Baret et
al., 1987; Curran et al., 2001; Pacumbaba, Jr. and Beyl, 2011).
Therefore, many optical vegetation indices have been ex-
plored pertaining to biochemical compositions in the leaf and
canopy levels to investigate the spectral differences among
the species (Blackburn, 1998; le Maire et al., 2004; Lovelock
and Robinson, 2002).
Previous studies have examined the potential of hyper-
spectral data in characterizing grapevine species, focusing
primarily on discriminating common varieties of Vitis vinifera
L. (Diago et al., 2013; Lacar et al., 2001; Parton et al., 2012;
Renzullo et al., 2006). Several attempts have been made to as-
sess the capability of airborne hyperspectral data for discrimi-
nation and mapping of grapevine varieties with some success
(Ferreiro-Armán et al., 2006, Lacar et al., 2001). Studies using
hyperspectral reflectance factor data to quantify the differ-
ences in spectral and biophysical properties of two closely
related rootstock grapevine species or their genotypes within
species have not been reported. Recent studies found that the
chance of success of species separability using satellite data
can be higher with multitemporal composite EO-1 Hyperion
images at 30 m spatial resolution (Somers and Asner, 2013).
Building on this work, here we attempt to differentiate two
grapevine species using remote sensing. This work is directly
relevant to the grape and wine industry because some vine-
yards are composed of unique hybrids derived from different
combinations of species or more commonly, different varietals
(genotypes). If species and genotypes could be differentiated
remotely, this opens up the possibility of identifying and
monitoring individual varietals remotely. This is particularly
important considering that the upcoming satellite-based
hyperspectral missions including Environmental Mapping
and Analysis Program (EnMap), Hyperspectral Infrared Imager
(HyspIRI) and Precursore Iperspettrale della Missione Ap-
plicativa (PRISMA ) will provide unparalleled opportunities
in satellite remote sensing of individual plant species and
their response to abiotic stress under climate change. These
developments call for further studies to explore the link
between field-measured hyperspectral spectra and available
or upcoming satellite hyperspectral missions, which allow
understanding the performance of spectral indices on crop
monitoring at leaf, canopy, and satellite scales without atmo-
spheric disturbance.
Work completed in this study provides an important base-
line for understanding the dynamics of differentiating species
and genotypes used in grapevine breeding. Specifically, the
research described here tests the following hypotheses: (a)
Spectral reflectance factor properties of two Vitis species are
unique and can be used to discriminate the species at the leaf,
canopy, and satellite levels, and (b) Spectral reflectance factor
properties differ among genotypes within species.
Materials and Methods
The Study Site Description
The fieldwork was conducted in two experimental plots at the
MBG, Saint Louis, Missouri (38°36'50.76"N, 90°15'32.04"W)
during the growing season of the study organisms. However,
only two measurements collected on 24 July and 07 August
2013 were used due to the optimal weather conditions in
these days. Thirty-three V. riparia (four genotypes, one to
eight clones/genotype) and 31 V. rupestris (five genotypes,
one to eight clones/genoytpe) were received from the United
States Department of Agriculture Grape Germplasm Research
Unit (USDA - GGRU) in Geneva, New York. Accessions arrived
as canes during Winter 2013. In the MBG greenhouses, the
canes were first stored in dark, cool conditions on a heating
pad from February through mid-April, and were then moved
into standard greenhouse conditions where leaf flush, flower
emergence, and in some cases, fruiting occurred. On 23 May
2014, the plants were transplanted into the common vineyard
in the Kemper Center for Home Gardening at MBG. The first
plot consisted of eight rows with three plants in each row.
The second plot contained 10 rows of four plants each. Rows
on both plots were oriented North-South and trained on a
single-wire vertical trellis system. The plots were separated
with a nearly two-meter wide sidewalk. Table 1 shows the
specific number of individual grapevine species and geno-
types studied in this paper.
Spectral Data Collection
Canopy reflectance, more specifically, hemispheric coni-
cal reflectance factor (HCRF; Schaepman-Strub et al., 2006)
was acquired between 12:00 to 1:00 pm local time, under
Table 1. Species and Genotypes Surveyed;
n = N umber of C lones per Genotype
Species Genotype n Total (species)
V. riparia GVIT 775 8
Okoboji 8
B 50 8
B 75 8
32
V. rupestris B 38 7
R-67-2 7
R-66-9 6
R-66-3 5
R-65-44 4
29
Total 61
52 January 2016 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING