Solar irradiance at the top of the atmosphere on a plane normal to the
incident radiation, and at the mean distance of the Earth from the Sun.
Solar irradiance is also referred to as the solar constant. In satellite
remote sensing, the solar irradiance is used as an onboard calibrartion of
visible band sensors. Some climate studies suggest that small variations
in the solar irradiance associated with solar activity over days to
decades may have an effect the Earth's climate.
