Downward irradiance Ed - the radiant flux (FI) on an infinitesimal element of the upper face (i.e. facing zenith) of a horizontal surface containing the point being considered, divided by the area of the element dA. Alternatively, downward irradiance is the integral of the radiance L, weighted by the cosine of the zenith angle (theta), over the upper hemisphere.
Pyranometers measure downward irradiance Ed at a horizontal surface of the sea or land integrated over a certain wavelength range, usually (unless a special Schott filter is used) close to the spectral range of the solar radiation at the earth surface.
| Data base symbol: | Ed-pyr(lambda),where lambda denotes the lower cut-off centre of a Schott filter (lambda=295 nm is assumed for the pyranometers measuring the total irradiance over the whole shortwave range of the solar spectrum). |
| Unit: | W/m2 |
| Type of recording: | time series, simultanous measurements of Ed-pyr(lambda) in 1 - 4 channels (various filters) |
| Data format: | ASCII |
| Average data set size: | a dozen kB. |
Supplementary parameters included in the downward irradiance data sets: