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Joshua Uebelherr
Ratio-Based Index (RVI)
This VI is attributed to Jordan (1969) and is simply the ration of near infrared (NIR) and red bands: RVI = NIR/red
Normalized Difference Vegetation Index (NDVI)
NDVI was first ascribed to by Rouse et al. (1973) though the concept was discussed by Kriegler et al. (1969): NDVI = (NIR-red)/(NIR+red). This is the most common VI and has a range of -1 to 1.
NDVI is calculated from the visible and near-infrared light reflected by vegetation. Healthy vegetation (left) absorbs most of the visible light that hits it, and reflects a large portion of the near-infrared light. Unhealthy or sparse vegetation (right) reflects more visible light and less near-infrared light. The numbers on the figure above are representative of actual values, but real vegetation is much more varied. (Illustration by Robert Simmon) (Nasa Earth Observatory Web Reference [1]).
Tassled Cap Analysis and the Soil Line
Kauth and Thomas (1976) first described the tassled cap pattern from a scatter-plot of red-NIR, the point of which is a region of dense vegetation with bare soil represented by the flat side opposite the point of the cap.
Perpendicular Vegetation Index (PVI)
This VI allows for soil lines of different slope but is highly sensitive to atmospheric variation: PVI = sin(a)NIR-cos(a)red; where a = the angle between the soil line and the NIR (Richardson and Wiegand, 1977).
Weighted Difference Vegetation Index (WDVI)
A parsimonious use of the concept from PVI with similar sensitivities, WDVI = NIR - g * red; where g is the soil line slope (Clevers, 1988).
Percentage Vegetation Index (PVI)
Crippen (1990) noticed that only the sum of NIR and red was the important use of the red band in NDVI and so merely used IPVI = NIR/(NIR+red) which constrains the values from 0 to 1, unlike the range of -1 to 1 for NDVI.
