Cloud-Aerosol LIDAR Infrared Pathfinder Satellite Observations (CALIPSO)

The Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission was a
collaborative effort between the NASA Langley Research Center (LaRC) and the Centre National
D’Etudes Spatiales (CNES) to study global radiative effects of aerosols and clouds on climate. CALIPSO
was launched on April 28, 2006 and began science data acquisition on June 13, 2006 until by mutual
agreement between NASA and CNES the science mission concluded on August 1, 2023. During this
period of time CALIPSO provided nearly continuous measurements of the vertical structure and optical
properties of clouds and aerosols to improve our understanding of their role in the Earth’s climate system
and to improve the performance of a variety of models ranging from regional chemical transport to global
circulation models used for climate prediction (Winker et al., 2010).

CALIPSO flew in the international A-Train constellation for coincident Earth observations from launch
until September 13, 2018, when CALIPSO began lowering its orbit from 705 km to 688 km (428 miles)
above the Earth to resume formation flying with CloudSat as part of the “C-Train”.

The CALIPSO payload consists of three co-aligned, near-nadir viewing instruments: a 2-wavelength
polarization-sensitive lidar, an imaging infrared radiometer (IIR), and a high-resolution wide field camera
(WFC). CALIOP is the name of the CALIPSO lidar and is an acronym for Cloud-Aerosol Lidar with
Orthogonal Polarization. The lidar profiles provide information on the vertical distribution of aerosols
and clouds, cloud particle phase, and classification of aerosol size. The CALIOP laser transmitter
subsystem transmits laser light simultaneously at 532 nm and 1064 nm at a pulse repetition rate of 20.16
Hz. The CALIOP receiver subsystem measures backscatter intensity at 1064 nm and at two orthogonally
polarized components of the 532 nm backscattered signal (Hunt et al., 2009).

The IIR provides medium spatial resolution nadir viewing images at 8.65, 10.6, and 12.05 µm, providing
information on cirrus cloud particle size and infrared emissivity. The WFC digital camera collects daytime
high spatial resolution imagery in the 620 - 670 nm wavelength range and is used to ascertain cloud
homogeneity, aid in cloud clearing, and provide meteorological context.

The Data Management System (DMS) uses the CALIPSO Automated Processing System (CAPS) to
convert the CALIPSO instrument data into scientific data products. A high level view of the CALIPSO
DMS is illustrated in the Top Level Data Flow Diagram shown in Figure 1. The data flow diagram depicts
the relationship between the data products and the subsystems that produce them. Circles in the diagram
represent algorithm processes called subsystems. Subsystems are a logical collection of algorithms, which
together convert input data products into output data products. Boxes with arrows entering a circle are
input data sources for the subsystem, while boxes with arrows exiting the circles are output data products.