Transcript Document
Soil-Adjusted Vegetation Index
A transformation technique to minimize soil brightness
from spectral vegetation indices involving red and nearinfrared (NIR) wave lengths.
The transformation involves a shifting of the origin of
reflectance spectra plotted in NIR-red wavelength space to
account for first-order soil-vegetation interactions and
differential red and NIR flux extinction through vegetated
canopies.
Near InfraRed (NIR)
Multispectral
Arizona Fire - USA
21-JUN-2003
In general, most vegetation indices rely in the
existence of a “soil line” in red and NIR
wavelength space, i.e., there is a principal axis
of soil spectral variation extending outward
from the origin with increasing brightness.
Since most of the soil spectra fall on or close o
the soil line, and since the intercept of such a
line is close to the origin, RVI and NDVI values
of bare soils (ratios) will be nearly identical for
a wide range in soil conditions.
Source: Huete, A.R. 1988
Figure 2
Source: Huete, A.R. 1988
NIR l2
red l1
NIR l2 red l1
NIR l2 red l1
Since the soil line has slope close to 1, the adjustment factors, l1
and l2, would be nearly equivalent. Shifting the red and NIR data
equally (l1=l2) and utilizing the NDVI format
NIR red
NIR red L
Where L=l1+l2=2l. Thus a soil adjustment index(SAVI) would only
involve an addition of a constant, L, to the denominator of the
NDVI equation.
However, in order to maintain the bounded cinditions ot the NDVI
equation (NDVI can vary from –1 to +1), a multiplication factor
(1+L) is needed in eq. 3
NIR red
SAVI
1 L
NIR red L
Figure 3
Source: Huete, A.R. 1988
Figure 4
Source: Huete, A.R. 1988
Figure 5
Source: Huete, A.R. 1988
MODIFIED-SAVI
2 NIR 1 2 NIR 1
MSAVI
2
2
8NIR red 0.5
Reference
• Huete, A.R. 1988. “A soil-Adjusted Vegetation Index (SAVI)”,
Remote Sensing of Environment, 25:295-309
•Huete, A.R., Lui, H.Q. 1994. “An Error and Sensitivity
Analysis of the Atmospheric and Soil- Correctin Variants of the
NDVI for he MODIS-EOS.” IEEE Transactions on Geoscience
and Remote Sensing, 32(4), 897-905