August 4, 2016



To reveal the secrets of clouds and aerosols

The purpose of the mission is to provide global measurements of aerosols and clouds required to obtain a better understanding of aerosols and clouds' role in the climate system, and to improve our abilities to predict long-term climate change and seasonal-to-interannual climate variability.
CALIPSO is an Earth science mission whose initial duration was of 3 years, but the mission was extended by 4 years. The satellite is part of the A-Train, it orbits the Earth at an altitude of 705 km, and a nominal inclination of approximately 98.2 degrees. Other satellites composing the A-Train are shown on the left.

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 was proved (IPCC report, 2001) that the main uncertainties about the climate evolution prediction are associated to the radiative impact of clouds and aerosols.

The understanding of the Earth's radiation budget requires the measurement of radiation fluxes at the top of the atmosphere and at different levels in the atmosphere.

The Lidar will characterize the vertical distributions and take into account multi-layer clouds.

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

CALIPSO will supply for the first time, over a three-year observation, a data collection of a global geographical cover with profiles (30-metre accuracy) measurements, and aerosol and cloud optical thickness measurements.

Zoom on the Scientific Objectives

First Objective

To supply a complete set of observations from which it will be possible to conduct the first evaluations based on aerosol direct radiative effect measurements.

The aerosols radiative forcing evaluations are calculated using aerosol transport models. The measurement synergy resulting from the EOS and CALIPSO missions is expected to lead to significant progress in model parametrization (optical thickness, vertical profile, simple diffusion albedo, and source intensity) and to reduce the current uncertainties related to radiative calculation.

Second Objective

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 Objective

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

The main uncertainty about this theme lies in not taking into account the multi-layer clouds which represent more than half of the cases. Thanks to the CALIPSO Lidar penetration capacities, the multi-layer systems will be solved, complementing the MODIS and CERES(on board the AQUA satellite) instruments data as entries to the radiation flux calculation.

Fourth Objective

To improve the knowledge of clouds' effect on climate through a better characterization of the thin cirrus, polar clouds and multi-layer clouds for which the passive imagery is ill-adapted.

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

Fifth Objective

To optimize Lidar / "large field" synergy

The validation of the geophysical products of large field sensors is always a heavy process because coincident in-situ observations are difficult to collect. Having quasi-simultaneous Lidar profiles permanently is a considerable asset for the AQUA validation. In return, after validating on the Lidar track, the "large field" products will enable to spatially stretch the properties deduced from the Lidar.

The quantization of the mission's scientific objectives is proposed by theme, aerosols then clouds. It is worth noting that by "construction", the ultimate performances will not be reached individually but will result from the four missions of the formation synergy—AQUA, CALIPSO, CLOUDSAT, and PARASOL.