# normalized.ratio.index: Normalised ratio index In hsdar: Manage, Analyse and Simulate Hyperspectral Data

## Description

Calculate normalised ratio index (nri) for a single given band combination or for all possible band combinations. Calculating nri is a frequently used method to standardize reflectance values and to find relationships between properties of the objects and their spectral data.

## Usage

 1 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 band number or wavelength. b2 Band 2 given as band number or wavelength. recursive If TRUE indices for all possible band combinations are calculated. If FALSE, only a single nri for the given bands in b1 and b2 is calculated. bywavelength Flag to determine if b1 and b2 are band number (bywavelength = FALSE) or wavelength (bywavelength = TRUE) values. ... 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.

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.

glm.nri, glm, Speclib, Nri
  1 2 3 4 5 6 7 8 9 10 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