The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite provides new insight into the role that clouds and atmospheric aerosols (airborne particles) play in regulating Earth’s weather, climate, and air quality.

CALIPSO combines an active lidar instrument with passive infrared and visible imagers to probe the vertical structure and properties of thin clouds and aerosols over the globe. CALIPSO was launched on April 28, 2006 with the cloud profiling radar system on the CloudSat satellite.

CALIPSO and CloudSat are highly complementary and together provide new, never-before-seen 3-D perspectives of how clouds and aerosols form, evolve, and affect weather and climate. CALIPSO and CloudSat fly in formation with three other satellites in the A-train constellation to enable an even greater understanding of our climate system from the broad array of sensors on these other spacecraft.


Convective Weather
A prototype system could provide commercial airline pilots with key weather and turbulence forecasts when flying over remote regions of the ocean where little real- or near-real-time data is available now. The NASA-funded system, being developed by the National Center for Atmospheric Research (NCAR), combines computer models and data from five operating NASA satellites with an artificial intelligence system to predict turbulence. The system is on track for testing next year, with the goal of ultimately giving pilots a regularly updated picture of potential storms over the ocean so that they can fly away from or around danger. This photograph, acquired in February 1984 by an astronaut aboard the space shuttle, shows a series of mature thunderstorms in southern Brazil.


Deep Convective Clouds
A 2009 astronaut photo from the International Space Station (ISS) of deep convective clouds, seen from above, over the Atlantic Ocean. Free standing and embedded towering convective clouds are particularly dangerous to aircraft flying over the open ocean.


Turbulence Waves and Deep Convection
NASA and NCAR are working to develop a near-real-time forecast that identifies turbulence from breaking gravity waves that are generated by rapidly rising deep convection. This image from NASA’s MODIS instrument (Moderate Resolution Imaging Spectroradiometer) shows gravity waves over the ocean. Atmospheric gravity waves (also called atmospheric internal waves) occur either when a uniform layer of air blows over a large obstacle, like a mountain or island or when rapidly rising, deep convection perturbs a stable layer from below, as in the oceanic case we have illustrated. When the air hits the obstacle or is disturbed by rising convection from below, the horizontal ribbons of uniform air are disturbed, which forms a wave pattern. This wave pattern in the air impresses itself onto sea waves when it touches the surface of the ocean. In addition to the surface mimicking the wave pattern, wave clouds can form as well, creating potential turbulence for aircraft.

In March 2009, the CALIPSO Team switched successfully from Laser 2 to Laser 1 as planned prior to launch. Since then, the performance of Laser 1 has been monitored, extensively analyzed and the results compared to Laser 2 performance. A new version of the Lidar Level 1 data set is being released. The maturity level definition of this release has been set to “Validated Stage 1.” This Version 3.00 release includes updated algorithms. At this time, browse images between March 12, 2009 to June 10, 2009 are posted on this web site and the data are available from the Atmospheric Science Data Center.

Video above: In 2006, CALIPSO was launched into orbit around the Earth as part of the “A-train,” a constellation of Earth observing satellites. CALIPSO provides the next generation of climate observations, including an advanced study of clouds and aerosols, drastically improving our ability to predict climate change and to study the air we breathe.

calipsoCALIPSO Overview

Aerosols are small particles suspended in the atmosphere. They have natural sources such as desert dust, sea salt, volcanic eruptions, and smoke from forest fires. They are also produced from the burning of coal, oil, and other fossil fuels; manufacturing chemicals; and driving cars and trucks.

When aerosol concentrations become high enough, they can pose serious health risks, especially to individuals with asthma and other respiratory problems. Airborne aerosols can also transport fungal and viral microbial pathogens, which can lead to disease outbreaks in other parts of the world.

Aerosols can affect weather and climate. They have complex properties. Depending upon their shapes, sizes and composition they can reflect sunlight back to space and cool the atmosphere, they can also absorb sunlight and warm the atmosphere. Aerosols can even change the lifetimes of clouds, how much rainfall can occur, and how they reflect sunlight. They further can enable chemical reactions to occur on their surfaces and influence the composition of the atmosphere.

Measurements from satellites and ground stations show that many aerosols remain in the environment for long periods and can be carried by the winds hundreds of miles from their origin. In other words, the air we breathe is strongly affected by other countries’ stewardship of the atmosphere — and vice versa.

To better predict the ultimate fate of aerosols, to help devise strategies for limiting pollution and to improve forecasts of harmful air quality conditions, we need better information on aerosol sources and how they enter the atmosphere and interact with weather patterns.


A key piece of information that is not provided by currently operating observational satellites is the altitude of aerosol layers in the atmosphere. Aerosols confined to the lowest part of the atmosphere are likely to be removed quickly by rain. On the other hand, those that are transported to higher altitudes are much more likely to travel long distances and affect air quality in distant countries. CALIPSO provides this vital missing piece of information.

Obtaining better information on the height of clouds is also needed. At present, weather prediction and climate models have considerable difficulty predicting the coverage, water and ice content and altitude of clouds. Inaccuracies in these parameters can lead to large errors in estimates of precipitation and the strength of the circulation. Observations from CALIPSO provide valuable new information that will help to improve weather and climate forecasts.

CALIPSO was selected as an Earth System Science Pathfinder satellite mission in December 1998 to address the role of clouds and aerosols in the Earth’s radiation budget.

CALIPSO is being developed through collaboration between NASA and the French space agency, Centre National d’Etudes Spatiales (CNES).

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite was selected as a NASA Earth System Science Pathfinder (ESSP) mission to address the role of clouds and aerosols in the Earth’s radiation budget.

Upon its launch in 2005, CALIPSO will provide the next generation of cloud and aerosol observations using lidar, or laser radar.

Scheduled to be launched simultaneously with another cloud observing satellite, CloudSat, CALIPSO will fly in formation with the “A-train,” a constellation of five satellites, including NASA’s EOS Aqua and Aura, and PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Science coupled with Observations from a Lidar), which is being developed by the French space agency, CNES.

NASA Langley Research Center is leading the mission and is providing overall project management, systems engineering, payload mission operations, data validation, processing and archival. CNES is providing a PROTEUS spacecraft, the imaging infrared radiometer (IIR), payload-to-spacecraft integration, and spacecraft mission operations.

CALIPSO will fly a three-channel lidar and passive instruments to provide key measurements of aerosol and cloud properties needed to improve climate predictions. CALIPSO is co-manifested with the CloudSat satellite for a 2004 launch on a Delta II launch vehicle. They both will operate as part of a constellation of satellites including EOS Aqua, EOS Aura, and PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Science coupled with Observations from a Lidar), which is being developed by CNES.

The satellites of the constellation will fly in a 705-km circular sun-synchronous polar orbit with a nominal ascending node equatorial crossing time of 13:30 local time. This constellation will provide nearly simultaneous and co-located observations that will allow numerous synergies to be realized by combining CALIPSO observations with complementary observations from other platforms. This unique data set of aerosol and cloud optical and physical properties and aerosol-cloud interactions will substantially increase our understanding of the climate system and the potential for climate change.

Together, CALIPSO and the other satellites of the constellation will provide:

  • a global measurement suite from which the first observationally-based estimates of aerosol direct radiative forcing of climate can be made,
  • a dramatically improved empirical basis for assessing aerosol indirect radiative forcing of climate,
  • a factor of 2 improvement in the accuracy of satellite estimates of longwave radiative fluxes at the Earth’s surface and in the atmosphere, and
  • a new ability to assess cloud-radiation feedback in the climate system.

CALIPSO takes advantage of the experience gained from the Lidar In-space Technology Experiment (LITE), which was developed by NASA Langley Research Center and flew on the Space Shuttle mission STS-64 in 1994. LITE provided the first demonstration of the capabilities of lidar to observe aerosols and clouds from space.

The CALIPSO mission builds on this LITE experience with a payload consisting of a two-wavelength polarization-sensitive lidar, and passive imagers operating in the visible and infrared spectral regions.

The lidar profiles provide information on the vertical distribution of aerosols and clouds, cloud ice/water phase (via the ratio of signals in two orthogonal polarization channels), and a qualitative classification of aerosol size (via the wavelength dependence of the backscatter). Data from the three instruments will be used together to measure the radiative and physical properties of cirrus clouds.


The Afternoon or “A-Train” satellite constellation presently consists of five satellites flying in formation around the globe (NASA’s Aqua and Aura satellites and CNES’ PARASOL satellite). The CALIPSO and CloudSat satellite missions were inserted in orbit behind Aqua in April 2006. Two additional satellites, OCO and Glory, will join the constellation in late 2008.

Each satellite within the A-Train has unique measurement capabilities that greatly complement each other. For the first time, near simultaneous measurements of aerosols, clouds, temperature, relative humidity, and radiative fluxes (the change of radiation in a layer) will be obtained over globe during all seasons. This ensemble of observations will allow one to understand how large scale aerosol and cloud properties change in response to changing environmental conditions. It will further allow one to determine how changing cloud and aerosols distributions influence our climate with greater clarity than possible before.

For much of its life, the A-Train will be maintained in orbit within 15 minutes of the leading and trailing spacecraft while traveling at over 15,000 miles per hour. CloudSat and CALIPSO will be controlled to an even finer requirement, within 15 seconds of each other, so that both instrument suites will view the same cloud area at nearly the same moment. This capability is crucial for studying clouds, which have lifetimes often less than 15 minutes.

The different instruments on each platform are described in Table 1: A-Train Instruments. + View Table 1


CALIPSO flies as part of the Aqua satellite constellation (or A-Train), which consists of the Aqua, CloudSat, CALIPSO, PARASOL, and Aura satellite missions. The constellation has a nominal orbital altitude of 705 km and inclination of 98 degrees. Aqua will lead the constellation with an equatorial crossing time of about 1:30 PM. CloudSat and CALIPSO lag Aqua by 1 to 2 minutes and will be separated from each other by 10 to 15 seconds.

The satellites in the A-Train are maintained in orbit to match the World Reference System 2 (WRS-2) reference grid. This reference system was developed to facilitate regular sampling patterns by remote sensors in the Landsat program. Each satellite completes 14.55 orbits per day with a separation of 24.7 degrees longitude between each successive orbit at the equator. The orbit tracks at the equator progresses westward 10.8 degrees on succeeding days, which over a 16-day period, produces a uniform WRS grid over the globe. The WRS grid pattern consists of 233 orbits with separation between orbits at the equator of 172 km. The Aqua satellite will be controlled to the WRS grid to within +/- 10 km. Additional information on the WRS can be obtained from the Landsat 7-WRS Web site. + View LandSat Site


Direct aerosol forcing and uncertainty. Estimates of aerosol forcing can be made using models or, increasingly, directly from observations. CALIPSO two-wavelength and depolarization profiles provide vertically resolved information on aerosol distribution, extinction coefficient, hydration state, and discrimination of large and small particles. CALIPSO also offers an improved cloud-masking capability. These observations will allow improved assessments of the representation of aerosol distribution and properties in models. Use of CALIPSO observations, alone and together with other A-train observations, will allow improved observational assessments of aerosol direct forcing as well as improvements in model-based assessments.

Indirect aerosol forcing and uncertainty. Changes in aerosol can potentially affect cloud reflectance and lifetime, but there are many uncertainties in how effective these mechanisms are in the real world. Regional assessments based on global datasets are needed. CALIPSO profiles will provide information on the vertical location of aerosols and whether or not they are in contact with, and therefore able to influence, clouds. CALIPSO also offers improved cloud masking of aerosol data, providing an opportunity to assess possible aerosol biases introducing uncertainties in current assessments of aerosol indirect effects.

Surface and atmospheric fluxes. The components of the atmospheric energy balance (in particular, SW and LW radiative fluxes) provide powerful constraints with which to test the performance of global climate models. Current global datasets of surface and atmospheric radiative fluxes contain significant uncertainties, largely due to the effects of clouds on radiation and in particular to effects of cloud multilayering. CALIPSO and Cloudsat will provide comprehensive observations of cloud height, thickness and layering. Coincident cloud observations from CALIPSO, CloudSat, and MODIS together with measurements of TOA fluxes from CERES provide an opportunity to create a greatly improved dataset of surface and atmospheric radiative fluxes, particularly in the polar regions.

Cloud-climate feedbacks. The fundamental problem in modeling cloud-radiation feedbacks involves the prediction of cloud properties based on atmospheric state and then using these properties to compute radiative fluxes. Testing these modeled processes requires nearly simultaneous observations of clouds, radiation, and atmospheric state. Cloud profiles from CALIPSO and CloudSat, cloud properties from MODIS/Aqua, radiative fluxes from CERES/Aqua, and measurements of atmospheric state from AIRS and AMSR (Aqua) provide the most complete closure of the cloud-radiation-atmospheric state feedback loop in the foreseeable future.


The CALIPSO payload consists of three co-aligned nadir-viewing instruments:

These instruments are designed to operate autonomously and continuously, although the WFC acquires data only under daylight conditions. Science Data are downlinked using an X-band transmitter system which is part of the payload. For more information on CALIPSO’s payload, visit these journal articles:

Winker, D. M., W. H. Hunt, and M. J. McGill, 2007: Initial performance assessment of CALIOP, Geophys. Res. Lett., 34, L19803, doi:10.1029/2007GL030135. [Download Paper (PDF)]

Winker, D. M., W. H. Hunt, and C. A. Hostetler, 2004: Status and Performance
of the CALIOP Lidar, Proc. SPIE vol 5575, 8-15. [Download Paper (PDF)]

The physical layout of the payload is shown below, with key instrument characteristics listed in the following table.


Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP)

CALIOP is a two-wavelength polarization-sensitive lidar that provides high-resolution vertical profiles of aerosols and clouds. Examples of this measurement capability can be found at the LITE and ICESAT homepages.

CALIOP utilizes three receiver channels: one measuring the 1064 nm backscatter intensity and two channels measuring orthogonally polarized components of the 532 nm backscattered signal. Dual 14-bit digitizers on each channel provide an effective 22-bit dynamic range. The receiver telescope is 1 meter in diameter. A redundant laser transmitter is included in the payload.

An active boresight system is employed to maintain co-alignment between the transmitter and the receiver. Ball Aerospace Corporation, developed the instrument.

laser: Nd: YAG, diode-pumped, Q-switched, frequency doubled
wavelengths: 532 nm, 1064 nm
pulse energy: 110 mJoule/channel
repetition rate: 20.25 Hz
receiver telescope: 1.0 m diameter
polarization: 532 nm
footprint/FOV: 100 m/ 130 µrad
vertical resolution: 30-60 m
horizontal resolution: 333 m
linear dynamic range: 22 bits
data rate: 316 kbps
Wide Field Camera (WFC)

The WFC is a modified version of the commercial off-the-shelf Ball Aerosopace CT-633 star tracker camera. It is a fixed, nadir-viewing imager with a single spectral channel covering the 620-670 nm region, selected to match band 1 of the MODIS (MODerate resolution Imaging Spectroradiometer) instrument on Aqua.

wavelength: 645 nm
spectral bandwidth: 50 nm
IFOV/swath: 125 m/61 km
data rate: 26 kbps
Imaging Infrared Radiometer (IIR)

A three-channel IIR is provided by CNES with algorithm development performed by the Institute Pierre Simon Laplace (IPSL) in Paris.

The IIR a nadir-viewing, non-scanning imager having a 64 km by 64 km swath with a pixel size of 1 km. The CALIOP beam is nominally aligned with the center of the IIR image.

The instrument uses a single microbolometer detecter array, with a rotating filter wheel providing measurements at three channels in the thermal infrared window region at 8.7 mm, 10.5 mm, and 12.0 mm. These wavelengths were selected to optimize joint CALIOP/IIR retrievals of cirrus cloud emissivity and particle size.

wavelengths: 8.65 µm, 10.6 µm, 12.0 µm
spectral resolution: 0.6 µm – 1.0 µm
IFOV/swath: 1 km/64 km
NETD at 210K: 0.3K
calibration: +/- 1K
data rate: 44 kbps