Greenhouse gases were long considered the only object worthy of study by scientists researching global warming. That was until work to model and measure the radiation budget, in particular at the LMD dynamic meteorology research laboratory in France, showed that natural or manmade aerosols play a crucial role in shaping climate. Indeed, according to the French science academy they could even be "the largest source of uncertainty in climate forcing calculations."

The Parasol mission, decided in 1999, aims to measure polarization and directionality of reflectances, especially in regions covered by the lidar on the Calipso minisatellite. Solar radiation becomes polarized when scattered by certain particles like aerosols, water droplets or ice crystals. Parasol will measure light polarized in different directions to gain a more precise characterization of clouds and aerosols than can be obtained by more traditional methods that measure their spectral signature.

Data collected by Parasol will allow us to establish the quantity and size distribution of aerosols over ocean regions, as well as their turbidity index over land surfaces, and to evaluate radiative forcing from solar radiation. They will also help to detect clouds, determine their thermodynamic phase and altitude, and estimate reflected solar flux. The integrated water vapour content will also be estimated.