Normalised ratio index

Description

Calculate normalised ratio index for a single given band combination or for all possible band combinations

Usage

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nri(x, b1, b2, recursive = FALSE, bywavelength = TRUE)

Arguments

x

List of class Speclib or of class Nri for print and as.matrix methods

b1

Band 1 given as index or wavelength

b2

Band 2 given as index or wavelength

recursive

If TRUE indices for all possible band combinations are calculated

bywavelength

Flag to determine if b1 and b2 are indices (bywavelength = FALSE) or wavelength (bywavelength = TRUE)

...

Further arguments passed to generic functions. Currently ignored.

Details

Function performs the following calculation:

nri_{B1,~B2}=\frac{R_{B1}-R_{B2}}{R_{B1}-R_{B2}};

with R being reflectance values at wavelength B1 and B2, respectively.

If recursive = TRUE, all possible band combinations are calculated.

Value

If recursive = FALSE, a data frame with index values is returned. Otherwise result is an object of class nri. See glm.nri for applying a generalised linear model to an array of normalised ratio indices.

Author(s)

Lukas Lehnert

References

Sims, D.A.; Gamon, J.A. (2002). Relationships between leaf pigment content and spectral reflectance across a wide range of species, leaf structures and developmental stages. Remote Sensing of Environment: 81/2, 337 - 354.

Thenkabail, P.S.; Smith, R.B.; Pauw, E.D. (2000). Hyperspectral vegetation indices and their relationships with agricultural crop characteristics. Remote Sensing of Environment: 71/2, 158 - 182.

See Also

glm.nri, glm, Speclib, Nri

Examples

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data(spectral_data)

## Calculate NDVI
ndvi <- nri(spectral_data, b1=800, b2=680)

## Calculate all possible combinations for WorldView-2-8
spec_WV <- spectralResampling(spectral_data, "WorldView2-8",
                              response_function = FALSE)
nri_WV <- nri(spec_WV, recursive = TRUE)
nri_WV

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