satellite (version 0.2.0)

calcEarthSunDist: 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"))

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" or "ESA".

Value

Numeric earth-sun distance (in AU).

Details

Computation of earth-sun distance using formulas provided by Spencer (1971), Mather (2005) or ESA.

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: Paul M. Mather (2005) Computer Processing of Remotely-Sensed Images: An Introduction. Wiley, 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.

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. http://www.nrel.gov/docs/legosti/old/2436.pdf.

Examples

# NOT RUN {
calcEarthSunDist(date = "2015-01-01", formula = "Spencer")
# }