In 2006, NASA and French Space Agency CNES launched a satellite in a joint mission to probe the properties of Earth's thin clouds and aerosols

In 2006, NASA and French Space Agency CNES launched a satellite in a joint mission to probe the properties of Earth's thin clouds and aerosols. The mission was called the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation, or CALIPSO. It was developed to study the vertical structure of clouds and atmospheric aerosols around Earth. CALIPSO worked with CloudSat and flew as part of the A-Train satellite constellation. The mission was designed to last three years but continued science operations for more than 17 years. It ended its science mission on August 1, 2023.

CALIPSO mission

CALIPSO was an Earth-orbiting satellite designed to observe clouds and aerosols. Aerosols are small particles suspended in the atmosphere. They can come from sources such as dust, pollution and volcanic ash. The satellite used lidar and infrared imaging to measure atmospheric layers. These observations gave scientists information about the height, structure and properties of clouds and aerosols.


CALIPSO was launched on April 28, 2006. It was launched together with CloudSat on a Delta II rocket from Vandenberg. The mission was an international partnership between NASA and the French space agency CNES. The satellite had an orbiter type mission and targeted Earth. Its main objective was to probe the properties of thin clouds and aerosols.

In 2006, NASA and French Space Agency CNES launched a satellite in a joint mission to probe the properties of Earth's thin clouds and aerosols

CALIPSO provided measurements that helped scientists study the role of clouds and aerosols in Earth's climate system. Before the mission, scientists had limited information about how these materials were distributed vertically through the atmosphere.

The satellite provided long-term global measurements of the vertical structure of multilayer clouds and aerosols. This allowed researchers to examine atmospheric layers that could not be studied in the same way using many other satellite instruments.

Clouds can affect how much solar energy enters Earth's atmosphere and how much heat leaves the planet. Aerosols can also influence radiation and cloud formation. CALIPSO measurements helped scientists improve estimates of these heating and cooling processes. The mission also provided information that was used in weather, climate and air-quality research.

Orbit and spacecraft facts

CALIPSO operated in a Sun-synchronous orbit. Until 2018, it operated at an altitude of about 705 kilometres as part of the A-Train. After 2018, its altitude was between about 685 and 705 kilometres as part of the C-Train.

Its orbital inclination was 98.2 degrees. One orbit took about 99 minutes. The satellite had a repeat cycle of 16 days. CALIPSO measured 1.49 metres by 1.84 metres by 2.31 metres. Its mass was about 600 kilograms, and its power system provided 582 watts.

The prime mission was planned for 22 months. Its design life was three years. The spacecraft continued operating for about 17 years. These figures show the difference between the original mission plan and the actual period during which CALIPSO produced scientific observations.

How CALIPSO studied the atmosphere?

CALIPSO carried three instruments that looked toward Earth. The main instrument was the Cloud-Aerosol Lidar with Orthogonal Polarization, known as CALIOP. The name is pronounced “caliope.” CALIOP was a two-wavelength polarization lidar. It sent laser pulses toward Earth and measured the returned signals. This allowed the instrument to identify clouds and aerosols and determine their vertical profiles.

The second instrument was the Imaging Infrared Radiometer, or IIR. It was a three-channel infrared imager. Its measurements complemented the lidar observations and provided additional information about clouds.

The third instrument was the Wide-Field Camera, or WFC. It was a single-channel, nadir-viewing push-broom visible imager. When combined with IIR measurements, WFC observations provided meteorological context around the lidar footprint. Together, the three instruments gave scientists information about atmospheric structures and the conditions surrounding the areas measured by the lidar.

CALIPSO and CloudSat

CALIPSO was launched together with CloudSat on April 28, 2006. The two satellites flew in close formation within the A-Train constellation. Their instruments provided complementary observations. CALIPSO used lidar, while CloudSat used radar. This combination allowed researchers to examine cloud structures and atmospheric particles using two different measurement methods.

The two missions created a record that helped scientists examine clouds and aerosols together. The observations improved understanding of the way these components interact with Earth's atmosphere. CloudSat left the A-Train in 2018 because of technical problems. CALIPSO later followed and continued observations while preserving the record created by the two missions.

What scientists learned from CALIPSO?

CALIPSO helped quantify how clouds and aerosols heat or cool the atmosphere. These processes are important because they can influence weather patterns and climate. Before CALIPSO, estimates of these heating and cooling rates had large uncertainties. The satellite's measurements helped reduce those uncertainties.

The mission also improved the way ice clouds and water clouds are represented in weather and climate models. Better cloud information can help models represent atmospheric processes with greater accuracy. CALIPSO also produced the first global survey of aerosol types. Its observations helped scientists follow the movement of dust, pollution and volcanic ash through the atmosphere.

Aerosols can travel across national borders and continents. Their movement can affect air quality and atmospheric conditions far from their original sources. CALIPSO data helped researchers study these transport pathways.

Other scientific findings

CALIPSO's lidar also produced observations beyond its main atmospheric objectives. The instrument detected patterns linked to ocean phytoplankton. These observations provided information about biological activity in the ocean.

The satellite also contributed to research into polar stratospheric clouds. These clouds form in the polar stratosphere and are connected with chemical processes involved in ozone depletion. Understanding these clouds is important for studying the formation of the ozone hole and the atmospheric processes that affect ozone.

Contribution to weather forecasting

CALIPSO's cloud detection measurements were also used to improve satellite-based weather observations. The mission helped improve operational weather-satellite retrievals. These retrievals are methods used to turn satellite measurements into information about atmospheric conditions.

Better cloud detection can help improve the accuracy of weather information. CALIPSO therefore contributed not only to long-term climate research but also to studies connected with day-to-day weather forecasting.

Spacecraft development

Thales Alenia Space was the prime contractor for the spacecraft. The company was formerly known as Alcatel Alenia Space. The company built the Proteus spacecraft bus used by CALIPSO. The Proteus platform had a design similar to the spacecraft bus used for Jason-1.

CNES provided funding for the spacecraft. The partnership between NASA and CNES allowed the mission to combine scientific and engineering resources from the United States and France. The Delta II launch vehicle carried CALIPSO into orbit from Vandenberg.

Why the mission matters?

CALIPSO changed the way scientists observe clouds and aerosols from space. Its long-term measurements provided information about the vertical distribution of atmospheric materials around the globe. The mission helped researchers study climate processes, weather systems and air quality. It also supplied information used to improve atmospheric models.

Its observations showed how dust, pollution and volcanic ash move through the atmosphere. They also provided information about cloud properties, phytoplankton patterns and polar stratospheric clouds.

The mission was designed for three years but continued for about 17 years. This extended period created a long record of atmospheric observations. CALIPSO concluded science operations on August 1, 2023. The mission's data remain part of the scientific record used to study Earth's atmosphere.