Preharvest Monitoring of Biomass Production - Engineering and Science of Biomass Feedstock Production and Provision - page 60

Fig. 4.1 Miscanthus growth height variation during different growing seasons

to quantify the concentrations of green leaf vegetation [ 9 ]. Linear combination from
two or more wave bands may be more sensitive and robust to assess the crop status
than a single band [ 10 ]. Generally, vegetation index can be divided into broadband
indices and narrowband indices according to the bandwidth of image data. The
broadband indices are calculated based on broadband refl ectance data, and the nar-
rowband indices are calculated using narrow spectral bands acquired by a spectrom-
eter or a hyperspectral image sensor [ 11 ]. There are more than 20 broadband
vegetation indices that have been designed to represent different crop information
from remote sensing images [ 12 ]. The Normalized Difference Vegetation Index
(NDVI) is the most commonly used vegetation index, and Gitelson et al. proposed
the Green Normalized Difference Vegetation Index (GNDVI), which substituted the
red band in the NDVI with the green band [ 13 ]. The GNDVI proves to be more use-
ful for assessing canopy variation in green crop biomass. The vegetation indices are
the indicators from refl ectance measurements and could be used to correlate with
dry matter estimation for perennial grasses. One of the potential biomass crops is
Miscanthus, which is a high yielding, perennial crop with good resistance against
disease, cold, and drought. To ensure proper growth of Miscanthus, it is essential to
know the plant stress, fertilization timing, physical parameters, and soil environ-
ment. Chapter 3 described the crop properties and also highlighted how these fac-
tors impact the successful establishment of a stable, high yielding stand. It is also
important to monitor and observe these parameters over the growing season.
Miscanthus grows higher and denser as the growing season progresses. As indicated
in Fig. 4.1 , a 2-month-old stand of Miscanthus grows faster, and the height of these
plants is approximately 50 cm. The 3-year-old stand of Miscanthus grows up to 3 m
high [ 14 ]. However, data acquisition is diffi cult due to lack of high clearance vehi-
cle operating as on-the-go sensing system for Miscanthus and other biomass