CALIPSO and the field campaigns: a convergence of interest for the study of clouds and aerosols
Résumé
The study of the Earth's meteorological atmosphere by satellite took off in the 1970s. The first
radiometric observations, however, provided very little vertical information until the more recent use
of active sounders. This coincided, in the 1980s, with the scientific community becoming aware that
better knowledge of cloud and aerosol properties and associated radiative forcing and interactions
was necessary for numerical weather prediction and the study of the climate. This search was
concretized by several major field experiments and the development of new active remote sensing
systems implemented in stations, airborne, balloon-borne and space platforms (the Lidar In-space
Technology Experiment was flown by NASA onboard the Space Shuttle Discovery in 1994).
CALIPSO and CloudSat platforms carrying active sounders were integrated into a constellation of
satellites (A-Train) led by the AQUA satellite in 2006. These satellites were placed in very close
orbits allowing co-located and almost simultaneous observations. This technological breakthrough
has enabled an unprecedented synergy for Earth observation. It is now clear that understanding
climatic and meteorological processes on local to global scales requires instrumental synergy
involving space-based resources, and more specifically lidar and radar observations. It has been
shown that a combination of observations made by well-dimensioned ground-based networks and
airborne measurements was essential to address process studies at various scales in field experiments.
Such synergies have been developed in major international programs supported by France and the
European community, often in collaboration with NASA. CALIPSO in the A-Train constellation was
a key element of these observations not just for a validation need, but also to learn from each other
and provide a scale extension.
French expertise in the field of active remote sensing for atmospheric measurement was crucial in
this approach, thanks to the development of new lidar and radar facilities and related synergetic
exploitation algorithms, as supported by CNRS and CNES. We will present examples of the
scientific results that have been made available to the international scientific community. The role of
CALIPSO observations will be highlighted in different parts of the globe, namely in the Tropics with
the African Monsoon Multidisciplinary Analysis (AMMA), the Aerosol, Radiation and Clouds in
southern Africa (AEROCLO-sA) or the Elucidating the Role of Clouds-Circulation Coupling in
Climate (EUREC4A) programs, in the Mediterranean and in the Arctic, as well as at the global scale
(via the exploitation of the synergetic products derived from the Lidar-Radar algorithms to constrain
radiation budget). The observations notably made it possible to evolve the physics of the models
leading to a reduction in radiative biases.
The climatological database obtained between 2006 and 2023 on clouds and aerosols from CALIPSO
and CloudSat now constitutes a reference for the long-term monitoring of clouds and aerosols and the
study of remarkable or extreme phenomena involving aerosol-cloud-dynamics interaction process
(cyclones, massive volcanic, dust or biomass burning aerosols transport across continents and oceans,
megafires, etc...). These missions will serve as a reference for the next EarthCare mission
(collaboration between the European Space Agency and the Japanese agency JAXA) and future ones