​Spectral Index algorithms calculate the relative magnitudes of wavelength components. The particular wavelength components used determine the product calculated. The example Notebook and tutorial here cover the following algorithms:

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Normalized Difference Vegetation Index (NDVI)

Represents the density of green (vegetation) on a patch of land. The pigment in plant leaves, chlorophyll, strongly absorbs visible light (from 0.4 to 0.7 µm) for use in photosynthesis. The cell structure of the leaves, on the other hand, strongly reflects near-infrared light (from 0.7 to 1.1 µm). The more leaves a plant has, the more these wavelengths of light are affected, respectively. NDVI = (NIR – Red) / (NIR + Red).

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Normalized Difference Buildup Index (NDBI)

A common index for detecting urbanization, where NDBI = (SWIR1 – NIR) / (SWIR1 + NIR). This index is similar to NBR (below).

Normalized Burn Ratio (NBR)

Similar to NDBI (reverse sign), this index is used to estimate burn severity. NBR = (NIR – SWIR1) / (NIR + SWIR1). Typical values are: <-0.1 for post fire regrowth, -0.1 to +0.1 for unburned, 0.1 to 0.27 for low-severity burn, 0.27 to 0.66 for moderate severity burn, and >0.66 for high severity burn.

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Normalized Difference Water Index (NDWI)

A common index for detecting water, where NDWI = (Green – NIR) / (Green + NIR).

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Modified Normalized Difference Water Index (mNDWI) or Normalized Difference Snow Index (NDSI)

A common index for detecting water (mNDWI) or snow (NDSI), where mNDWI = NDSI = (Green – SWIR1) / (Green + SWIR1).

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Soil Adjusted Vegetation Index (SAVI)

A vegetation index adjusted for soil response, where SAVI = (NIR – Red) / (NIR + Red + 0.5)*1.5.

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Enhanced Vegetation Index (EVI)

An "optimized" vegetation index designed to enhance the vegetation signal with improved sensitivity in high biomass regions. Landsat EVI = 2.5 * (NIR – Red) / ( NIR + 6*Red – 7.5*Blue + 1).

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Fractional Cover (FC)

Estimates the average vegetation fractional cover using a linear un-mixing technique developed by Juan P. Guerschman (CSIRO). Each pixel is classified as a fraction of bare soil (BS), photosynthetic vegetation (PV), and non-photosynthetic vegetation (NPV).

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Spectral Variability Vegetation Index (SVVI)

An index by Lloyd Coulter (San Diego State University) based on the standard deviation of a Landsat 7 time series mosaic, where SVVI = STD (1,2,3,4,5,7) – STD (4,5,7). This algorithm has been used to detect forests and agriculture.