fromSolarZenith: Compute hour angle and time from the solar zenith angle

Description Usage Arguments Note References See Also Examples

Description

Compute the solar hour angle and the time difference from noon associated therewith from the sun zenith angle.

Usage

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## S4 method for signature 'numeric'
fromSolarZenith(theta, phi, n, formula = c("Cooper",
  "Spencer"))

## S4 method for signature 'Raster'
fromSolarZenith(theta, phi, n, formula = c("Cooper",
  "Spencer"), daytime = c("AM", "PM"), origin = strptime("1993-01-01",
  "%Y-%m-%d"), ...)

Arguments

theta

numeric or Raster* object, sun zenith angle in degrees (see Note).

phi

numeric or Raster* object, latitude in EPSG:4326 (see http://spatialreference.org/ref/epsg/wgs-84/).

n

Date object from which to extract the day of the year (DOY), passed to declination.

formula

character, formula from which to calculate the angular declination of the sun, see declination.

daytime

character, possible options are "AM" (i.e., morning scene) and "PM".

origin

A POSIX* object that defines the origin of x, see solarHourAngle.

...

If theta is a Raster* object, further arguments passed on to writeRaster.

Note

Negative and positive solar hour angles indicate solar zenith angles during the morning and afternoon, respectively. Note that the sun zenith angle can easily be derived from the elevation angle through sun zenith = 1 - elevation.

References

PVEducation (2016) Elevation angle. Available online at http://www.pveducation.org/pvcdrom/properties-of-sunlight/elevation-angle.

See Also

declination, solarHourAngle.

Examples

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theta <- 30 # 30 deg zenith angle
delta <- declination(Sys.Date(), "Spencer", "degrees") # angular declination
phi <- 0    # geographic latitude, i.e. equator

fromSolarZenith(theta, delta, phi) 

environmentalinformatics-marburg/satelliteTools documentation built on March 24, 2018, 4:08 a.m.