January 23, 2024



Revealing the secrets of clouds and aerosols

The mission’s goal is to provide global measurements of aerosols and clouds required to obtain a better understanding of their role in the climate system, and to improve our ability to predict long-term climate change and seasonal-to-interannual climate variability.

CALIPSO is an Earth science mission initially planned to last three years, but was extended to the end of 2023. The satellite is part of the A-Train, orbiting the Earth at an altitude of 705 kilometres with a nominal inclination of approximately 98.2 degrees. 

The CALIPSO instrument suite measures vertical distributions of aerosols and clouds in the atmosphere, as well as the optical and physical properties of aerosols and clouds, which influence the Earth's radiation budget.

It has been proved (IPCC report, 2001) that the main uncertainties surrounding the prediction of climate change stem from the radiative impact of clouds and aerosols.

Understanding Earth's radiation budget requires the measurement of radiation fluxes at the top of the atmosphere, on the ground and at different levels in the atmosphere.

The lidar characterizes vertical distributions and is able to sense multi-layer clouds.

A key stage for factoring in the role of clouds more effectively in climate models is to have simultaneous measurements of the atmosphere’s state, microphysical, and optical properties, as well as cloud radiative properties.

CALIPSO was the first satellite to provide global coverage to measure profiles (30-metre accuracy) and aerosol and cloud optical thickness.

Science Goals

First Goal

To supply a complete set of observations from which it will be possible to obtain the first estimates based on measurements of the direct radiative effect of aerosols.

Estimates of radiative forcing are calculated using aerosol transport models. Measurement synergies between the EOS and CALIPSO missions are expected to lead to significant advances in model parametrization (optical thickness, vertical profile, single-scattering albedo and source intensity) and to reduce current uncertainties related to radiative calculations.

Second Goal

To supply a measurement base to improve the autization of aerosol indirect effects at global and regional scales.

The Lidar is particularly well adapted to the study of aerosol-cloud interactions: it enables a good cloud detection, and aerosol and cloud separate identification. Its performances to detect the aerosols with low optical thickness, i.e. when the interaction with clouds is at its highest, are an additional asset.

The joint measurement of the radiative budget with CERES on board AQUA will provide a complete set of measurements  for this sensitive issue.

Third Goal

To achieve a twofold improvement in accuracy the satellite's estimation of long-wave radiation fluxes.

The main uncertainty here lies in not factoring in multi-layer clouds, which represent more than half of cases. Thanks to CALIPSO’s lidar penetration capabilities, multi-layer systems can be resolved, complementing data from the MODIS and CERES instruments on Aqua for radiation flux calculations.

Fourth Goal

To gain new insights into clouds' effect on climate through better characterization of thin cirrus, polar clouds and multi-layer clouds for which passive imagery is ill-suited.

Simultaneous characterization of atmospheric state (Aqua), cloud properties (CALIPSO, Aqua/MODIS) and radiation fluxes (Aqua/CERES).

Fifth Goal

To optimize lidar/wide-field synergies

Validating geophysical products of wide-field sensors is always a cumbersome process because coincident in-situ observations are difficult to collect. Having quasi-simultaneous lidar profiles permanently is a considerable asset for validating Aqua data. In return, after validating on the lidar track, the wide-field products enable the properties deduced from the lidar to be extended spatially.

Quantification of the mission's science goals encompasses aerosols and then clouds. It is worth noting that ultimate performance are not achieved individually but result from the synergies between the four missions in the formation,—Aqua, CALIPSO, CloudSat and PARASOL.