The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
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2. STUDY SITE AND HYPERSPECTRAL 
DATA COLLECTION 
2.1 Study Site 
The City of Tampa was selected as study area. It is the largest 
city on the west coast of Florida consisting of approximately 
285 sq. km. The population is increasing and is currently 
estimated at approximately 335,000 people (www.tampagov.net 
accessed on Nov. 26, 2007). The city is located at 
approximately 28° N and 82° W (Figure 1). Historically, the 
natural plant communities of the Tampa Bay region included 
pine flatwoods, cypress domes, hardwood hammocks, high pine 
forests, freshwater marshes, and mangrove forests. Based on the 
City of Tampa Urban Ecological Analysis (Campbell and 
Landry, 1999), important, dominant urban tree species include 
American Elm (Ulmus americana), Bluejack Oak (Q. incana), 
Crape Myrtle (Lagerstroemia indica), Laurel Oak (Q. 
laurifolia), Live Oak (Q. virginiana), Southern Magnolia 
(.Magnolia grandiflora), Persimmon (Diospyros virginiana), 
Red Maple (Acer rubrum), Sand Live Oak (Q. geminata), 
American Sycamore (Platanus occidentalis), Turkey Oak (Q. 
laevis), Slash Pine (Pinus elliottii), and Longleaf Pine (Pinus 
palustris). Other dominant tree species within the City of 
Tampa include Cabbage Palm (Sabal palmetto), Queen Palm 
(Syagrus romanzoffiana), Citrus (Citrus spp.), Goldenrain Tree 
(Koelreuteria paniculata), Bottlebrush (Callistemon viminale), 
and Water Oak (Q. nigra), etc. In this analysis, a total of 11 
broadleaf species (Table 1) were selected for testing the 
capability of in situ hyperspectral data for discriminating 
between species. Note that shorthand abbreviations for tree 
species discussed throughout this paper can be found in Table 1 
in parentheses after the common name of the tree species. 
Figure l.A location map of the study area 
2.2 In Situ Hyperspectral Data Collection 
A full-range Analytical Spectral Device (ASD) (FieldSpec®3, 
Analytical Spectral Devices, Inc., U.S.) was used to collect 
spectral reflectance measurements from the 11 broadleaf tree 
species in the city area, which are a subset of urban forest 
species within the Tampa Bay area. The ASD instrument 
consists of three separate spectrometers and covers a spectral 
range of 350 nm to 2500 nm. 
Tree species 
Number of trees Train samples Test samples 
Total 
American Elm (Elm) 
25 
22 
12 
34 
Bluejack Oak (Blue) 
20 
17 
8 
25 
Crape Myrtle (Crap) 
20 
27 
13 
40 
Laurel Oak (Laur) 
31 
24 
13 
37 
Live Oak (Live) 
26 
24 
11 
35 
Southern Magnolia (Magn) 
20 
30 
16 
46 
Persimmon (Pers) 
29 
22 
11 
33 
Red Maple (Mapl) 
27 
24 
12 
36 
Sand Live Oak (Sand) 
23 
25 
12 
37 
American Sycamore (Syca) 
16 
25 
12 
37 
Turkey Oak (Turk) 
28 
22 
12 
34 
Total 
265 
262 
132 
394 
Table 1. Spectral measurements taken from 11 broadleaf 
species. 
In the field, at least 20 trees of each species (except Syca) were 
measured to account for spectral variation and spatial 
distribution. The spectral measurements were collected from 
top, middle and low foliage branches from the crowns of 
individual species. Tree heights lower than 7 m for most 
sampled trees were generally selected because of the logistical 
difficulties with measuring spectra from the top of tall trees. A 
ladder with an effective height of 5 m was used for collecting 
spectral measurements. To ensure that relatively pure spectra 
from individual trees of difference species were collected, the 
data acquisition was executed with a careful selection of view 
area from tree foliage branches to avoid or lessen the effect of 
background on target spectra. One to three spectra were 
collected from individual trees. Because of the difficulty in 
separating a shadow/shaded area from a sunlit area from a tree 
crown, only fully sunlit areas were measured. Each spectral 
measurement was repeated ten times to obtain reliable mean 
and variance estimates. In this manner, a total of 394 spectral 
measurements were collected from the different foliage 
branches of the 11 broadleaf species in the City of Tampa 
(Table 1). 
3. ANALYSIS METHODS 
3.1 Preprocessing of Spectral Measurements 
The following preprocessing of spectral measurement was 
performed. First, spectral curves were truncated below 400 nm 
and above 2400 nm because the measurements were extremely 
noisy outside of this range. Approximately 2000 bands remain, 
each with a width of about 1 nm. Next, curve smoothing was 
used with a simple average over blocks of five neighboring 
bands. The spectral curves for constant area were then 
normalized by dividing the mean reflectance for that curve. 
That is, a spectral reflectance curve p, was replaced 
PO 
, where, k represents the total bands of the 
spectral reflectance. The benefit of such normalization is the 
suppression of illumination differences. Figure 2(a) shows a 
plot of unnormalized curves versus band wavelength for two 
observations of each of the five oak species (Blue, Laur, Live, 
Sand and Turk). Figure 2(b) shows the same curves of Figure 
2(a) after normalization. Notice that the clearer separation 
between the species over a wide range of wavelength in Figure 
2(b). Figure 2(c) shows a plot of normalized curves versus band 
wavelength for all the 11 species (Elm through Turk). 
3.2 Extraction of Spectral Variables 
Forty-six spectral variables (Table 2), including normalized 
spectra, derivative spectra, spectral vegetation indices, spectral