R: Compute top of atmosphere solar irradiance using radiation...

calcTOAIrradRadRef {satellite} | R Documentation

## Compute top of atmosphere solar irradiance using radiation vs. reflection

### Description

Compute extraterrestrial solar irradiance (ESun) using the actual maximum radiation and reflection values within each band.

### Usage

    ## S4 method for signature 'Satellite'
    calcTOAIrradRadRef(x, normalize = TRUE, esd)

    ## S4 method for signature 'numeric'
    calcTOAIrradRadRef(x, ref_max, normalize = TRUE, esd)

### Arguments

`x` | A Satellite object or the maximum radiance of satellite band(s) as numeric object.
`normalize` | Logical; if `TRUE`, ESun is normalized to mean earth-sun distance.
`esd` | Earth-sun distance (AU, can be estimated using `calcEarthSunDist`). If x is a Satellite object and esd is not supplied and necessary for normalization, it is tried to take it from the metadata, otherwise it is estimated by the day of the year using `calcEarthSunDist`.
`ref_max` | Maximum reflextance of satellite band(s).

### Details

The actual solar irradiance is computed using the following formula taken from the GRASS GIS i.landsat.toar module

ESun = (pi d^2) RADIANCE_MAXIMUM / REFLECTANCE_MAXIMUM

where d is the earth-sun distance (in AU) and RADIANCE_MAXIMUM and REFLECTANCE_MAXIMUM are the maximum radiance and reflection values of the respective band. All these parameters are taken from the scene's metadata file if a Satellite object is passed to the function.

By default, the resulting actual ESun will be normalized to a mean earth-sun distance to be compatible with other default results from `calcTOAIrradTable` or `calcTOAIrradModel`.

### Value

If x is a Satellite object, a Satellite object with ESun information added to the metadata; if x is numeric, a vector containing ESun for the respective band(s).

### See Also

`calcTOAIrradTable` for tabulated solar irradiance values from the literature or `calcTOAIrradModel` for the computation of the solar irradiance based on look-up tables for the sensor's relative spectral response and solar irradiation spectral data.

See `calcEarthSunDist` for calculating the earth-sun distance based on the day of the year which is called by this function if ESun should be corrected for actual earth-sun distance.

### Examples

    path <- system.file("extdata", package = "satellite")
    files <- list.files(path, pattern = glob2rx("LC08*.TIF"), full.names = TRUE)
    sat <- satellite(files)
    sat <- calcTOAIrradModel(sat)
    getSatESUN(sat)

    calcTOAIrradRadRef(x = getSatRadMax(sat, getSatBCDESolar(sat)),
                       ref_max = getSatRefMax(sat, getSatBCDESolar(sat)),
                       normalize = FALSE,
                       esd = calcEarthSunDist("2015-01-01"))

[Package satellite version 1.0.1 Index]