The Earth’s radiation budget is the balance between the incoming radiation from the Sun and the outgoing reflected and scattered solar radiation plus the thermal infrared emission to space. A number of instruments contribute to measurements of these parameters. The discussion here focuses on those instruments specifically designed to study radiation budget as their sole or primary mission.
In general, different instruments are used to measure the different components of the radiation budget:
— to cover the full range of incoming solar radiation (0.2 – 4.0 μm);
— to monitor the long-wave emitted Earth radiation (3 – 100 μm);
— to measure the reflected short-wave radiation from the Earth.
The instruments offer high radiometric accuracy to provide accurate absolute measurements (~ 1 W/m2 is needed). Most radiometers have a narrow field of view and are used to measure the radiance in a particular direction. Using this, together with information on the angular properties of the radiation, the flux may be obtained. Advanced instruments have a directional capability and channels which allow study of the anisotropy and polarisation characteristics of the radiation fluxes.
To provide the much needed improvement of temporal sampling of the Earth radiation budget (ERB), observations by the Geostationary Earth Radiation Budget (GERB) instrument on EUMETSAT’s Meteosat 8 and 9 are being used. This instrument provides measurements of the ERB every 15 minutes, providing a unique view of the diurnal cycle.