R: Compute earth-sun distance based on day of the year

calcEarthSunDist {satellite} | R Documentation

## Compute earth-sun distance based on day of the year

### Description

The earth-sun distance for a particular day of the year is computed based on one of several empirical formulas.

### Usage

    calcEarthSunDist(date, formula = c("Spencer", "Mather", "ESA", "Duffie"))

### Arguments

`date` | Date of the sensor overpass; either a character string in a native date format (e.g. "YYYY-MM-DD", see `as.Date`) or a POSIX* object (see `as.POSIXct`).
`formula` | Formula to be applied, specified through the name of the author, i.e. one of "Spencer", "Mather", "ESA" or "Duffie" (see 'Details').

### Details

Computation of earth-sun distance using formulas provided by Spencer (1971), Mather (2005) or ESA. If `formula = "Duffie"`, the inverse squared relative earth–sun distance is returned as proposed by Duffie and Beckman (1980).

### Value

Numeric earth-sun distance (in AU) or, if `formula = "Duffie"`, the relative squared earth–sun distance on the given day.

### References

The formulas are taken from the following sources:

- Spencer: Spencer JW (1971) Fourier series representation of the position of the sun. Search 2/5. Taken from https://goo.gl/lhi9UI.

- Mather: Mather PM (2005) Computer Processing of Remotely-Sensed Images: An Introduction. Wiley: Chichester, ISBN: 978-0-470-02101-9, http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0470021012.html.

- ESA: ESA Earth Observation Quality Control: Landsat frequently asked questions.

- Duffie: Duffie JA, Beckman WA (2013) Solar Engineering of Thermal Processes. Wiley: Hoboken, New Jersey, ISBN: 978-0-470-87366-3, http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0470873663.html.

See also: Bird R, Riordan C (1984) Simple solar spectral model for direct and diffuse irradiance on horizontal and tilted planes at the Earth's surface for cloudless atmospheres. Task No. 3434.10, Solar Energy Research Institute: Golden, Colorado, http://www.nrel.gov/docs/legosti/old/2436.pdf.

### Examples

    calcEarthSunDist(date = "2015-01-01", formula = "Spencer") # absolute
    calcEarthSunDist(date = "2015-01-01", formula = "Duffie")  # relative

[Package satellite version 1.0.1 Index]