The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
472 
2. METHODS 
2.1 Study area and sampling 
The study site is located in Majella National Park, Italy (latitude 
41°52' to 42° 14' N, longitude 13°14' to 13° SOI). The park 
covers an area of 74,095 ha and extends into the southern part 
of Abruzzo, at a distance of 40 km from the Adriatic Sea. The 
region is situated in the massifs of the Apennines. The park is 
characterized by several mountain peaks, the highest being 
Mount Amaro (2794 m). Coordinates (x y) were randomly 
generated in a grassland stratum to select plots. A total of 45 
plots (30 m x 30 m) were generated and a GPS (Global 
Positioning System) was used to locate them in the field. To 
increase the number of samples in the time available, four to 
five randomly selected subplots were clustered within each plot. 
This resulted in a total of 191 subplots being sampled. The 1 m 
x 1 m subplots differed in species composition and relative 
abundance while the within-subplot variability was small. 
were randomly selected in each subplot, and their SPAD 
readings were recorded. From the 30 individual SPAD 
measurements, the average was calculated (Table 1). These 
averaged SPAD readings were converted into leaf chlorophyll 
content (units: pg cm" 2 ) by means of an empirical calibration 
function provided by Markwell et al. (1995). The total canopy 
chlorophyll content (CCC; units: g m" 2 ) for each subplot was 
obtained by multiplying the leaf chlorophyll content by the 
corresponding LAI. 
Measured 
variables 
Min 
Mean 
Max 
StDev 
Range 
LAI (m 2 m" 2 ) 
0.39 
2.76 
7.34 
1.50 
6.95 
CCC (g m" 2 ) 
0.1 
0.87 
2.7 
0.55 
2.56 
Table 1. Summary statistics of the measured biophysical and 
biochemical variables of grassland sample subplots (n=191); 
CCC is the canopy chlorophyll content. 
2.2 Canopy spectral measurements 
Fifteen replicates of canopy spectral measurements were taken 
from each subplot, using a GER 3700 spectroradiometer 
(Geophysical and Environmental Research Corporation, 
Buffalo, New York). 
The fiber optic, with a field view of 25°, was handheld 
approximately 1 m above the ground at nadir position. The 
ground area observed by the sensor of GER had a diameter of 
45 cm and was large enough to cover the center of the subplots 
without being influenced by the surroundings. The 15 replicate 
spectral measurements taken from each subplot enabled to 
suppress much of the measurement noise by averaging the 
replicate measurements. Prior to each reflectance measurement, 
the radiance of a white standard panel coated with BaS04 and 
of known reflectivity was recorded for normalization of the 
target measurements. The fieldwork was conducted between 
June 15 and July 15 in 2005. To minimize atmospheric 
perturbations and BRDF effects, spectral measurements were 
made on clear sunny days between 11:30 a.m. and 2:00 p.m. 
2.3 LAI measurements 
In each subplot, LAI was non-destructively measured using a 
widely used optical instrument, the Plant Canopy Analyzer 
LAI-2000 (LICOR Inc., Lincoln, NE, USA). A detailed 
description of this instrument is given by LI-COR (1992) and 
Welles and Norman (1991). In this study, measurements were 
taken either under clear skies with low solar elevation (i.e., 
within the two hours following sunrise or preceding sunset) or 
under overcast conditions. The LAI measurements were taken 
on the same day that the canopy spectral measurements were 
made. To prevent direct sunlight on the sensor of LAI-2000, 
samples of below- and above-canopy radiation were made in 
the direction facing away from the sun (i.e., with the sun behind 
the operator), using a view restrictor of 45°. For each subplot, 
reference samples of above-canopy radiation were determined 
by measuring incoming radiation above the grass subplot (in an 
open area). Next, five below-canopy samples were collected 
and used to calculate the average LAI (Table 1). 
2.4 Chlorophyll measurements 
A SPAD-502 Leaf Chlorophyll Meter (Minolta, Inc.) was used 
to assess the leaf chlorophyll content (LCC) in each 1 m x 1 m 
subplot. A total of 30 leaves representing the dominant species 
2.5 Data analysis 
We selected the normalized difference vegetation index (NDVI) 
(Rouse et al., 1974) as a representative of ratio indices, and the 
second soil-adjusted vegetation index (SAVI2) (Major et al., 
1990) as a representative of soil-based indices, for the analysis 
in this study. The narrow band NDVI and SAVI2 indices were 
systematically calculated for all possible (584 x 584 = 341,056) 
band combinations between 400 nm and 2400 nm. The soil line 
parameters were calculated from soil spectral measurement of 
bare soils which were acquired from few subplots with no 
vegetation. We assumed that the measured soil optical 
properties were representative for the study area. Consequently, 
the soil line parameters were considered constant for all 191 
subplots. 
For this study, we used two methods to calculate the red edge 
inflection point (REIP). The linear interpolation method (Guyot 
and Baret, 1988) assumes that the spectral reflectance at the red 
edge can be simplified to a straight line centered around a 
midpoint between (i) the reflectance in the NIR shoulder at 
about 780 nm, and (ii) the reflectance minimum of the 
chlorophyll absorption feature at about 670 nm. First, the 
reflectance value is estimated at the inflection point. Then, a 
linear interpolation procedure for the measurements at 700 nm 
and 740 nm is applied to estimate the wavelength corresponding 
to the estimated reflectance value at the inflection point: 
^red-edge 
REIP, 
(^670 ^78o)/2 
_ - 700 + 40 
R _ D 
red-edge lx j 
- R-, 
(1) 
(2) 
where the constants 700 and 40 result from interpolation 
between the 700 nm to 740 nm intervals, and R^o, R?oo> R740 
and R780 are, respectively, the reflectance values at 670 nm, 700 
nm, 740 nm and 780 nm. 
The linear extrapolation method (LEM) (Cho and Skidmore, 
2006) is based on the linear extrapolation of two straight lines 
(Eqs. 3 and 4) through two points on the far-red (680 nm to 700 
nm) and two points on the NIR (725 nm to 760 nm) flanks of 
the first derivative reflectance spectrum (D) of the red edge 
region. The REIP is then defined by the wavelength value at the 
intersection of the straight lines (Eq. 5).