Dataset containing wavelengths and tabulated values for spectral irradiance for the sun both above the terrestrial atmosphere and at ground level under clear sky. The different spectra in this collection are from ASTM G173 standard and other published sources.
Format
A "source_mspct" object containing 5 "source_spct"
objects.
In each of the member spectra, the variables are as follows:
w.length (nm)
s.e.irrad (W m-2 nm-1)
Details
The effect of the pass of solar radiation depends on the elevation angle of the sun above the horizon as it affects the distance light travels through the atmosphere. This frequently expressed as equivalent air mass. AM0 is used for extraterrestrial normal solar irradiance (its integral is called the solar constant). AM1 represents the terrestrial solar spectrum at sea level with the sun located at the zenith. AM1.5 is commonly used as a reference suitable for mid-latitudes. The AM0 spectrum changes very little with time, while AM1.5 being at ground level is dependent on the composition of the atmosphere and affected by water vapour and ozone concentrations as well as by particulate matter and ground surface optical properties.
Irradiance describes a flux of energy onto a plane. The plane is usually located horizontally and receives light from the sun (direct radiation) and from the sky (diffuse radiation). Global radiation is the sum of direct and diffuse. A variation is to quantity direct radiation separately from diffuse radiation on a plane normal to the direction of the sun, called direct normal irradiance. Independently of the units used in the sources of the data, all these data are stored with wavelengths expressed in nanometres \((n)\) and spectral energy irradiances \((W\,m^{-2}\,nm^{-1})\).
The three different AM0 spectra differ mainly in the range of wavelengths they cover. The two AM1.5 spectra are for simulations for typical clear sky conditions at mid-latitudes and a sun elevation of 41.81 degrees.
ASTM.E490.AM0 is the mean extraterrestrial solar spectrum,
for air mass zero (AM0).
Gueymard.AM0 is Gueymard's (2004) extraterrestrial solar spectrum,
for air mass zero (AM0). Used as the basis for calculating the terrestrial
solar spectra defined by ASTM G173.
WMO.Wehrli.AM0 is Wehrli's (1985) extraterrestrial solar spectrum,
for air mass zero (AM0). Used the World Meteorological Organization (WMO).
ASTM.G173.global is global spectral irradiance for air mass 1.5
(AM1.5). Reference Spectrum Derived from SMARTS v. 2.9.2 for AM1.5. (solar
zenith angle 48.19)
ASTM.G173.direct is direct spectral irradiance for air mass 1.5
(AM1.5). Reference Spectrum Derived from SMARTS v. 2.9.2 for AM1.5. (solar
zenith angle 48.19)
Metadata are stored as attributes in each of these spectral data objects
and can be accessed with methods
what_measured(),
how_measured() and comment().
References
ASTM (2012) ASTM G173 Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37 degrees Tilted Surface.
Gueymard, C. A. (2004) The sun's total and spectral irradiance for solar energy applications and solar radiation models. Solar Energy, 76, 423-453. doi:j.solener.2003.08.039 .
Wehrli, C. (1985) Extraterrestrial solar spectrum. Pub. No. 615, World Radiation Center, Davos, Switzerland.
Examples
summary(sun_reference.mspct)
#> Summary of source_mspct [5 x 1] object: sun_reference.mspct
#> # A tibble: 5 × 8
#> spct.idx class dim w.length.min w.length.max colnames multiple.wl time.unit
#> <chr> <chr> <chr> <dbl> <dbl> <list> <dbl> <Duratio>
#> 1 ASTM.E49… sour… [1,6… 120. 1000000 <chr> 1 1s
#> 2 ASTM.G17… sour… [2,0… 280 4000 <chr> 1 1s
#> 3 ASTM.G17… sour… [2,0… 280 4000 <chr> 1 1s
#> 4 Gueymard… sour… [2,0… 280 4000 <chr> 1 1s
#> 5 WMO.Wehr… sour… [920… 200. 10075 <chr> 1 1s
what_measured(sun_reference.mspct)
#> # A tibble: 5 × 2
#> spct.idx what.measured
#> <fct> <chr>
#> 1 ASTM.E490.AM0 AM0 extraterrestrial solar spectrum
#> 2 ASTM.G173.direct AM1.5 direct normal terrestrial solar spectrum
#> 3 ASTM.G173.global AM1.5 global terrestrial solar spectrum
#> 4 Gueymard.AM0 AM0 extraterrestrial solar spectrum
#> 5 WMO.Wehrli.AM0 AM0 extraterrestrial solar spectrum