sunAngle: Solar Angle as Function of Space and Time Based on...
In MariekeDirk/wrdc: Solar radiation data from the WRDC archive

Description Usage Arguments Value Author(s) References See Also Examples

View source: R/quality_control.R

Solar Angle as Function of Space and Time Based on NASA-provided Fortran program, in turn (according to comments in the code) based on "The Astronomical Almanac".

1	sunAngle(t, longitude = 0, latitude = 0, useRefraction = FALSE)

`t`	time, a POSIXt object (converted to timezone `"UTC"`, if it is not already in that timezone), or a numeric value that corresponds to such a time.
`longitude`	observer longitude in degrees east
`latitude`	observer latitude in degrees north
`useRefraction`	boolean, set to `TRUE` to apply a correction for atmospheric refraction

A list containing the following.

`time`	time
`azimuth`	azimuth, in degrees eastward of north, from 0 to 360. (See diagram below.)
`altitude`	altitude, in degrees above the horizon, ranging from -90 to 90. (See diagram below.)
`diameter`	solar diameter, in degrees
`distance`	distance to sun, in astronomical units

Dan Kelley

Based on Fortran code retrieved from ftp://climate1.gsfc.nasa.gov/wiscombe/Solar_Rad/SunAngles/sunae.f on 2009-11-1. Comments in that code list as references: Michalsky, J., 1988: The Astronomical Almanac's algorithm for approximate solar position (1950-2050), Solar Energy 40, 227-235 The Astronomical Almanac, U.S. Gov't Printing Office, Washington, D.C. (published every year). The code comments suggest that the appendix in Michalsky (1988) contains errors, and declares the use of the following formulae in the 1995 version the Almanac:

p. A12: approximation to sunrise/set times;
p. B61: solar altitude (AKA elevation) and azimuth;
p. B62: refraction correction;
p. C24: mean longitude, mean anomaly, ecliptic longitude, obliquity of ecliptic, right ascension, declination, Earth-Sun distance, angular diameter of Sun;
p. L2: Greenwich mean sidereal time (ignoring T^2, T^3 terms).

The code lists authors as Dr. Joe Michalsky and Dr. Lee Harrison (State University of New York), with modifications by Dr. Warren Wiscombe (NASA Goddard Space Flight Center).

The equivalent function for the moon is moonAngle.

rise <- as.POSIXct("2011-03-03 06:49:00", tz="UTC") + 4*3600
set <- as.POSIXct("2011-03-03 18:04:00", tz="UTC") + 4*3600
mismatch <- function(lonlat)
{
    sunAngle(rise, lonlat[1], lonlat[2])$altitude^2 + sunAngle(set, lonlat[1], lonlat[2])$altitude^2
}
result <- optim(c(1,1), mismatch)
lon.hfx <- (-63.55274)
lat.hfx <- 44.65
dist <- geodDist(result$par[1], result$par[2], lon.hfx, lat.hfx)
cat(sprintf("Infer Halifax latitude %.2f and longitude %.2f; distance mismatch %.0f km",
            result$par[2], result$par[1], dist))