GIS and Earth Observation University

1. NDVI

The spectral signature of wholesome vegetation shows a abrupt rise of the reflection level at 0,7 µm, whereas land without vegetation, according to the type of surface, has a continuous linear course. So much more active the chlorophyll of the plants, so much bigger is the boost of the reflection level at the near infrared (0,78 - 1 µm). Beside the determination between of the vegetation and other objects it allows to detect the vitality of the vegetation.

The NDVI results from the following equation:

NDVI = (Bnear_IR - Bred) / (Bnear_IR + Bred)

2. SAVI ( Soil Adjusted Vegetation Index)

This index attempts to be a hybrid between the ratio-based indices and the perpendicular indices. The reasoning behind this index acknowledges that the isovegetation lines are not parallel, and that they do not all converge at a single point. The initial construction of this index was based on measurements of cotton and range grass canopies with dark and light soil backgrounds, and the adjustment factor L was found by trial and error until a factor that gave equal vegetation index results for the dark and light soils was found. The result is a ratio-based index where the point of convergence is not the origin.

3. TSAVI (Transformed Soil Adjusted Vegetation Index)

This index assumes that the soil line has arbitrary slope and intercept, and it makes use of these values to adjust the vegetation index. This would be a nice way of escaping the arbitrariness of the L in SAVI, if an additional adjustment parameter had not been included in the index. The parameter X was adjusted so as to minimize the soil background effect. The value reported in the papers is 0.08. The convergence point of the isovegetation lines lies between the origin and the usually-used SAVI convergence point (for L = 0.5).  

The TSAVI results from the following equation:

TSAVI = s * (Bnear_IR - s * Bred - a) / (a * B near_IR + Bred - a * s + X * ( 1 + s * s ))  

where:    - a is the soil line intercept    - s is the soil line slope    - X is the adjustment factor to minimize soil noise.

4. MSAVI (Modified Soil Adjusted Vegetation Index)

The adjustment factor L for SAVI depends on the level of vegetation cover being observed. This leads to the circular problem of needing to know the vegetation cover before calculating the vegetation index, which is what gives you the vegetation cover. The basic idea of MSAVI was to provide a variable correction factor L. The correction factor used is based on the product of NDVI and WDVI. This means that the isovegetation lines do not converge to a single point.  

The MSAVI results from the following equation:

MSAVI = (1 + L) * (B near_IR - Bred) / (Bnear_IR + Bred + L)  

where: L = 1 - 2 * s * NDVI * WDVI and s is the soil line slope

5. DVI (Difference Vegetation Index)

his is the simplest vegetation index:    - Sensitive to the amount of vegetation    - Distinguishes between soil and vegetation    - Does NOT deal with the difference between reflectance and radiance caused by the atmosphere or shadows  

The DVI results from the following equation:

DVI = (Bnear_IR - Bred)

6. GNDVI (Green Normalized Difference Vegetation Index)

The authors verified that GNDVI was more sensible than NDVI to identify different concentration rates of chlorophyll, which is highly correlated at nitrogen. The use of green spectral band was more efficient than the red spectral band to discriminate nitrogen.   

The GNDVI results from the following equation:

GNDVI = (Bnear_IR - Bgreen) / (Bnear_IR + Bgreen)