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", "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').
Value
Numeric earth-sun distance (in AU) or, if formula = "Duffie",
the relative squared earth--sun distance on the given day.
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).
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.
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.
# NOT RUN {calcEarthSunDist(date = "2015-01-01", formula = "Spencer") # absolutecalcEarthSunDist(date = "2015-01-01", formula = "Duffie") # relative# }