Clouds and aerosols have a major influence on Earth’s radiation budget and climate processes.

By reflecting solar radiation, clouds reduce the amount of energy penetrating the atmosphere, thereby cooling the planet. But they also trap infrared radiation from the surface of the globe, which produces an opposite, warming greenhouse effect.

Likewise, by absorbing and scattering light, aerosols have a direct, so-called parasol effect that cools the surface of Earth. They also have an indirect effect on the radiation budget, impacting cloud condensation by altering their reflectivity and lifetime, which increases the intensity of precipitations.

So, the challenge facing us is clear: How do we gain a closer understanding of these direct and indirect effects?

The lidar on the Calipso minisatellite enables estimations of long-wave radiative flux twice as accurate as anything achieved before.

Calipso also aims to learn more about how clouds affect climate through better characterization of cirrus, polar and multilayer clouds.

The Calipso mission is part of the A-Train space observatory. This formation of 5 French-U.S. satellites constitutes an unprecedented opportunity to obtain near-simultaneous, co-located observations of atmospheric phenomena, using different measuring techniques.

Calipso and Parasol, the 2 satellites with which CNES is involved, acquire complementary measurements to Cloudsat, Aqua and Aura American satellites, over the same areas of the globe.

Parasol, launched in December 2004, measures the polarization of light reflected by clouds and aerosols towards the satellite. It is therefore a passive system. Calipso is an active system that emits a light wave and then measures the amount of energy backscattered by the different layers of the atmosphere.

The A-Train must be initially constituted by 6 satellites. OCO, the last missing, was lost just after its launch, on February 24, 2009.