Fig 3.3.1.3.1: Earthshine and solar irradiance spectra 425..450 nm

Image: AT2-ELS

Satellite-borne spectrometers can measure the spectra of two sources of radiation: the spectrum of the irradiance — that is, the solar radiation before the radiation reaches the Earth's atmosphere — and the spectrum of the earthshine, — that is, the radiation leaving the Earth.

The differences between the two spectra are caused by the interactions of solar radiation with the atmosphere and/or surface of the Earth. Among these interactions are the species-specific absorptions we wish to measure.