nri | R Documentation |

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.

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

`x` |
List of class |

`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 |

`bywavelength` |
Flag to determine if b1 and b2 are band number (bywavelength = FALSE) or wavelength (bywavelength = TRUE) values. |

Function for `nri`

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.

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

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`

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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