Geoscience Reference
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Figure 1. Location of the study areas.
NORMALIZED DIFFERENCE VEGETATION INDEX (NDVI)
Seven cloud-free SPOT images (1996/11/08, 1999/03/06, 1999/10/31, 2000/11/27,
2001/11/20, 2003/12/17, and 2004/11/19) of the Chenyulan watershed were purchased
from the Space and Remote-sensing Research Center, Taiwan. The NDVI images of
the study area were generated from SPOT HRV images with a resolution of 20 m ac-
cording to the following equation:
NIR
R
NDVI
=
R
(1)
NIR
+
where NIR and R are near-infrared and visible-red spectral data, respectively. The
NDVI values range from 1 to +1; a high NDVI value represents a large amount of high
photosynthesizing vegetation (Jensen, 1996b).
Variogram and Kriging Estimation
In geostatistical methods, variograms can be used to quantify the observed relation-
ship between the values of samples and the proximity of samples (Lin et al., 2008d).
Following the work of Garrigues et al. (2006), Garrigues et al. (2008b), and Lin et al.
(2008), NDVI data are considered values of punctual regionalized variable. An experi-
mental variogram for interval lag distance class h, γ(h), is represented by
()
nh
1
2 nh
() =
(
) Zx i
()
2
(2)
γ
h
Zx i +
h
()
i
=
1
 
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