CALIPSO Final Report

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission was a pioneering international partnership between NASA and the French Space Agency, CNES. Launched on 28 April 2006 into the A-Train’s 705 km orbit altitude, CALIPSO’s measurements filled a crucial, well-recognized need for high-resolution atmospheric profiles, and proved essential in reducing the uncertainties that limit our understanding of the roles of aerosols and clouds in the Earth’s global climate system. The 3-year nominal mission was completed on 28 April 2009, and the project was granted mission extensions following NASA Earth Science Division (ESD) Senior Reviews in 2009, 2011, 2013, 2015, 2017, and 2020. CNES held similar mission reviews, known as REvue D’Extension de Mission (REDEM), and participated in and concurred with all ESD mission extension decisions.

The CALIPSO instrument suite consisted of CALIOP (i.e., the Cloud-Aerosol Lidar with Orthogonal Polarization), a two-wavelength, polarization-sensitive elastic backscatter lidar, a three-channel Imaging Infrared Radiometer (IIR), and a single-channel Wide Field-of-view Camera (WFC). Since routine science operations began on 12 June 2006, data were collected almost continuously and all instruments performed exceptionally well. The lidar’s primary laser delivered over 1.6 billion shots before a slow pressure leak in the laser canister left the laser susceptible to anomalous electrical discharges that caused unacceptable reductions in laser pulse energies. The primary laser was taken out of service on 16 February 2009. The backup laser was activated on 12 March 2009, and performed superbly, generating over billion shots in 14+ years of operation. The canister for the backup laser also had a slow pressure leak that eventually caused intermittent low energy laser pulses. While these low energy pulses had the potential to seriously degrade science data quality, the development and application of innovative data handling methods largely minimized their effects.

In September 2018, CALIPSO exited the A-Train and descended to its disposal orbit at 688 km to resume matched lidar/radar cloud profile measurements with CloudSat. All spacecraft and platform subsystems continued to operate nominally in the new C-Train orbit. Because fuel reserves were depleted, CALIPSO’s orbit slowly drifted to later local ascending node crossing times, leading to compromised power margins. The science phase of the mission was terminated in June 2023 while end of mission activities for the spacecraft continued until December 2023 when the platform was passivized.

The CALIPSO project routinely produced and archived a comprehensive catalog of standard and expedited data products that were distributed to scientific researchers worldwide through data centers in the United States and France. The expedited products were designed to meet the near-real-time data delivery requirements of active field campaigns and operational forecast centers. To date there have been five comprehensive releases of the standard data products, with each new release offering substantial improvements in retrieval accuracies and uncertainty characterization. These products have been extensively validated and reported in peer-reviewed literature. The CALIPSO data have been embraced throughout the science community, as evidenced by the publication ~5000 studies in peer-reviewed journals.

CALIPSO’s co-aligned lidar and IIR measurements and robust retrieval techniques led to significant advances in retrieving cloud and aerosol distributions and optical properties, both by themselves and in synergy with CloudSat and the other A-Train instruments. Observationally-based estimates of all- sky aerosol direct radiative effect were made possible by CALIPSO’s unique ability to measure aerosols in cloudy skies. CALIPSO directly observed cloud altitude and thermodynamic phase, providing key new insights in understanding the feedbacks between Arctic cloud cover, sea ice extent and life cycle, and the thinning of Greenland’s ice sheets. CALIPSO’s vertical profile measurements of clouds and aerosols provided an unprecedented resource for evaluating weather and climate models, air quality models, and models used to forecast the dispersion of volcanic and fire plumes.

CALIPSO was truly a pathfinder spaceborne lidar mission. Not only did its measurements open doors to new scientific discoveries and applications that benefit society, but the team also created innovative techniques and tools to analyze a new class of Earth science observations. The mission learned that lidar profile observations are highly valued by operational weather centers for improving the skill of their forecasts and can uniquely address a broad spectrum of scientific questions. The mission also demonstrated that lasers could operate in space for long periods and that the measurement technique is stable and resilient – if proper preparations are taken. Indeed, the 17-year climate data record established by CALIPSO’s continuous global measurements now provides an invaluable reference dataset that is widely used by the science community to better understand the processes that influence climate. In many ways, the knowledge and wisdom gained from CALIPSO paved the way forward for other space-based lidar missions: International Space Station (ISS)/CATS lidar and the European Space Agency (ESA) EarthCare/ATLID as two successful missions to date. Future missions such as Italian Space Agency (ASI) Luce and the German Aerospace ES MERLIN are also leaning heavily on the experiences learned from CALIPSO.