The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008
292
classification and forest type mapping using hyperspectral
images.
2. MATERIALS AND METHODS
2.1. Study sites
The test site for this study is located in the research Forest of
University of Tehran located in Mazandaran province in the
north of Iran, which is a part of the Caspian forest (figure .1).
This forest is divided to seven districts with a total area of
845 ha.
Figure 1: study site location in the Caspian forest (a), the
photo of mountainous view of the Caspian forest in study
area
2.2. Sample collection
Species Alder
Hornbeam
Beech
Ironwood
Oak
No. of trees j ^
sampled
20
29
15
19
Altitude(m) ^59
700-100
400-
2200
400-
590
700-
1320
DBH (cm) 38-61
35-68
40-70
28-36
42-70
Height (m) 27-36
15-25
25-38
15-22
35-60
Branch level:
(3R‘*2S 2 *2E 3 *N 3 )
228
240
348
180
228
Leaf level:
(3R*2S*2E *N)
228
240
348
180
228
Twig:(6R*N)
120
120
174
90
114
Branch: (6R*N)
120
120
174
90
114
'R, number of repeats or cut branches 2 -S, leaf surface,
adaxial/abaxial- 3 E, exposed, illuminated/shaded- 4 N, number of tree
sample for each species
Table 1: The attribute table of number of each species and
some measured characteristics
To sample a representative set of different types of leaves,
branches were harvested in two exposed conditions,
illuminated and shaded leaves, at various levels ranging from
the upper to the lower position in the canopy. A total of 2448
spectrum for leaves from 102 samples of five tree species
were analyzed. The samples were collected at three sites in
altitude gradient between 400 and 2100m (low, mid and high
elevation) in August and September 2007. For each species
the samples were chosen from dominant-stairs trees in
different DBH (diameter at breast height). Table 1 shows the
attribute table of number of each species and measured
characteristics.
2.3. Spectroradiometry measurements
Reflectance measurements were done using a ASD Fieldspec
Pro spectroradiometer (350-2500 nm) in the course of
summer 2007. The sensor, with a field of view of 25°, was
positioned 30-40 cm above the samples at nadir position.
Prior to each three measurement, a white reference panel with
approximately 100% reflectance was used as a reference
standard. The measurements were conducted under clear and
cloudless sky between 10:00 and 14:00 at local time. For
each tree individual three branches have been cut in shade
and sun exposed condition. At first, the spectral
measurements of branch-leaves pile has been done and after
removing the leaves, spectral leave pile was acquired from
adaxial and abaxial surfaces.
2.3. Methods
Vegetation indices
A variety of indices related to total chlorophyll changes were
used to characterize complex spectra and make comparisons
possible among species and between illumination conditions.
These indices have been derived from the list that Maire et al.
(2004) presented based on knowledge of the reflectance
properties of chlorophyll content described in other literatures.
Total chlorophyll is correlated with the red edge position
which is the wavelength X (in nanometers) of the maximum
slope of the reflectance spectrum at wavelength between 690
and 740 nm. The depths and widths of pigment absorption
troughs and the position and magnitude of reflectance peaks
can be quite different among species (Ustin et al. 1993).
Vegetation
index
Equation
Reference
mND 705 :
modified
Normalized
difference
(R750-
^-705X( R-750+R705-
2R445)
Sims & Gamon
2002
Simple Ratio
R750/R700
Gitelson et al
1996
m SR705l
modified
(R75O-R445)/( R705-
Sims & Gamon
Simple Ratio
R445)
2002
Vogelmann
index
R740/R72O
Vogelmann et al
1993
Datt index
(R850-
R-71oV( R-850+R-680 )
Datt 1999
Table 2: Vegetation indices used to estimate chlorophyll
content at leaf level.
Variations in chlorophyll content can be caused by structural
status of the leaves, atmospheric pollution, nutrient
deficiency, toxicity, plant disease, and radiation stress (Filella
& Penuelas 1999, Clevers et al., 2005). Although these
factors influence the chlorophyll content within the species or
individual trees we hypothesized that the chlorophyll changes