CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations)
CALIPSO, alias PICASSO-CENA (Pathfinder Instruments for Cloud and Aerosol Spaceborne Observations / Climatologie Etendue des Nuages et des Aerosols), and alias ESSP-3 (Earth System Science Pathfinder-3), is a satellite science mission, a collaborative NASA/CNES project in the ESSP (Earth System Science Pathfinder) program of NASA. Other project partners (algorithm development, etc.) are Hampton University in Hampton, VA, and IPSL (Institut Pierre Simon Laplace), Jussieu, France.
The overall science objective of the mission is to profile the vertical distribution of clouds and aerosols and their role in the heating/cooling of the Earth (improve of estimates for direct and indirect radiative forcing, improve accuracy of long-wave radiative fluxes at the Earth's surface and within the atmosphere, assessment of cloud feed back in the climate system). The study of cloud and aerosols radiative impacts is within the GCRP (Global Climate Research Program) of WMO providing in particular inputs for GEWEX (Global Energy and Water Cycle Experiment) and CLIVAR (CLImate VARiability and predictability). 1) 2) 3) 4) 5) 6) 7) 8)
The mission is managed by NASA/LaRC. CNES supplies the S/C and an IR imaging sensor (of IASI heritage). NASA/LaRC provides the main instrument suite (a Ball-built lidar sensor) and S/C launch services aboard a Taurus launch vehicle. CNES provides S/C operations, the payload operations center is located at LaRC.
Figure 1: Artist's rendition of the CALIPSO spacecraft (image credit: CNES)
The S/C employes an enhanced Proteus bus (of Jason-1 heritage), developed by Thales Alenia Space (prime contractor, formerly Alcatel Alenia Space), and funded by CNES. The platform structure has has dimensions of 2.46 m (height) x 1.51 m x 1.91 m. When deployed the solar arrays extend to 9.72 m. All the equipment units are accommodated on four lateral panels; the hydrazine mono-propellant system with a 40 liter tank and four 1 N thrusters are positioned on and under the lower plate. 9)
The S/C is three-axis stabilized. The normal in-orbit platform attitude control is based on a gyro-stellar concept. Three accurate 2-axis gyroscopes are used for stability requirements and attitude propagation. Attitude acquisition is obtained using magnetic and solar measurements (two 3-axis magnetometers and eight coarse sun sensors). The AOCS can provide yaw steering. Four small reactions wheels generate a torque for attitude control, they are de-saturated using magnetic torquers. The pointing attitude restitution is 0.05º (3 σ) on each axis. Accurate attitude determination is based on two star trackers (nominal and redundant) measurements. Both star trackers are accommodated on the payload in the STA (Star Tracker Assembly), equipped with an autonomous thermal control (the star trackers, SED16, were built at EADS Sodern). Each star tracker has a 25º circular FOV and includes a CCD detector (1024 x 1024) which is regulated to a temperature of -10ºC by a Peltier device. A GPS receiver provides satellite position information for accurate orbit ephemeris determination and onboard time delivery.
Figure 2: Line drawing of the CALIPSO spacecraft (image credit: NASA)
Figure 3: Internal layout of the Proteus bus (image credit: Thales Alenia Space)
Figure 4: Functional block diagram of the Proteus bus (image credit: Alcatel Alenia Space)
Electric power is generated by two symmetric wing arrays attached near to the satellite center of mass with two single axis stepping motor mechanisms. Each wing is constituted of four 1.5 x 0.8 m panels covered with classical silicon cells. The power is distributed through a single non-regulated primary electrical bus (23/37 V with an average 28 V voltage), using a Li-Ion battery (9 series-3 parallel technology) developed by SAFT, France. Up to 16 switchable power lines (5 A max) can be provided to the payload.
The DHU (Data Handling Unit) performs its tasks through the OBC (MA 31750 processor). It supports all onboard functions including the management of the communication links with every satellite unit, including the payload, either via discrete point-to-point lines, or via a MIL-STD-1553-B bus. The S/C mass is 635 kg including 28 kg of hydrazine, power = 560 W (average). The design life is 3 years.
Figure 5: Illustration of the SED 26 star trackers (image credit: EADS Sodern)
Orbit: The CALIPSO spacecraft is part of the formation flight in the so-called “A-train” (Aqua in the lead and Aura at the tail) or afternoon constellation. Near sun-synchronous orbit, altitude = 705 km, inclination = 98.05º, the ascending node crossing time is around 13:30 hours.
All members of the A-train employ the WRS-2 (World Reference System-2), a global catalog notation system for data which enables a user to inquire about satellite imagery (ground coverage in any repeat cycle) over any portion of the world by specifying a nominal scene center designated by PATH and ROW numbers. However, CALIPSO and CloudSat are not using the WRS-2 reference. CALIPSO is controlled to a customized grid shifted 215 km east from the WRS-2. And CloudSat is flying in close formation with CALIPSO (12.5 ± 2.5 s ahead of it).
Observation strategy: The train consists of the following S/C: Aqua, CloudSat, CALIPSO, PARASOL, and Aura. The objective is to provide a coincident set of data on aerosol and cloud properties, radiative fluxes and atmospheric state essential for accurate quantification of aerosol and cloud radiative effects. The formation flight of CALIPSO with Aqua and CloudSat includes the following constraints:
• CALIPSO shall maintain the formation with Aqua
• CloudSat shall maintain the formation with CALIPSO.
The CALIPSO orbit is maintained so that a target area can be observed within 6 minutes of each other (CALIPSO and Aqua). The relevant Aqua instruments for CALIPSO are: CERES, MODIS, AIRS, and AMSR-E.
Figure 6: Illustration of formation flight configuration in the A-Train (image credit: NASA/CNES)
RF communications: An onboard data storage capability of 60 Gbit is provided for the payload data and 2 Gbit for platform housekeeping data. TT&C communications are in S-band with data rates of 727 kbit/s for telemetry (QPSK modulation) and 4kbit/s for telecommands. The payload data are transmitted in X-band at 80 Mbit/s. The CCSDS packet standard protocol is used for telemetry encoding and telecommand decoding.
• The CALIPSO mission exploitation has been extended until the end of 2015. Beginning in 2015, another 2 years extension will be studied by the 2 agencies (Ref. 13).
• The CALIPSO spacecraft and its payload are operating nominally in 2012. 13)
• The CALIPSO spacecraft and its payload are operating nominally in 2011.
The CALIPSO mission has provided the first multi-year global dataset of lidar aerosol and cloud profiles. CALIOP active profiling in conjunction with A-Train and CALIPSO passive observations are opening new fields of investigation into the role of aerosols and clouds in the climate system, from direct comparison with model outputs and ongoing developments in data assimilation. 15)
• In late April 2010, the CALIPSO spacecraft completed its 4th year in orbit. Since the laser switch in March 2009, the mission continues nominally and the laser performances are excellent. 16)
• The spacecraft and its payload are operating nominally in 2010. NASA requested a mission extension in the A-Train to the end of 2011. In 2009 the Senior Review Panel recommended to NASA that an extended mission status will lead to more fundamental science results. In addition, the synergy between CALIPSO and other A-train components is vital and the measurements are crucial as a bridge to the next satellite lidar mission: the ADM (Atmospheric Dynamics Mission), the European Space Agency lidar scheduled for launch in 2011, as well as EarthCARE (2013) and ACE (2015). 17) 18) 19)
• In April 2009, CALIPSO resumed operations after switching from its primary to its backup laser in March 2009. The backup laser was designed into CALIPSO to make it robust, in case the primary laser became unreliable. The value of the planning came to the forefront early in 2009 as the primary laser began to behave erratically, due to a slow pressure leak in the laser's canister. The backup laser provided its first observation data on March 12, 2009. The instrument then resumed normal operations and is undergoing a calibration review now. The release of standard data products should resume in late April 2009. 20) 21) 22)
• In Dec. 2006, the CALIPSO mission started the distribution of its data products. This data release consists of data beginning in mid June 2006 and includes Level 1 radiances from each of the instruments. This release also includes the lidar Level 2 vertical feature mask and cloud and aerosol layer products. The CALIPSO data are available through the Atmospheric Science Data Center (ASDC) at NASA/LaRC.
• Since mid-June 2006, CALIPSO has joined the A-train and the satellite is in routine operations. CALIPSO is controlled to ± 10 km at equator crossing.
• After launch, the spacecraft underwent a commissioning phase of 38 days. Based on telemetry data, the pointing performance of the spacecraft is < 0.02º about each axis. 23)
Sensor complement: (CALIOP, IIR, WFC)
The payload consists of three co-aligned nadir viewing instruments: CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization), IIR (Imaging Infrared Radiometer), and WFC (Wide-Field Camera).
Figure 7: Overview of the CALIPSO payload (image credit: NASA)
Figure 8: Payload elements and configuration (image credit: BATC)
Figure 9: The CALIPSO payload consists of the CALIOP lidar and two passive sensors (image credit: NASA/LaRC, BATC)
• CALIOP has a two-wavelength laser transmitter and a three-channel receiver
• The IIR is a three-channel infrared radiometer
• The WFC is a visible imager with a single channel.
The two passive sensors image a 60 km swath centered on the lidar footprint. 24)
CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization):
CALIOP is provided by NASA/LaRC (built by Ball Aerospace and Technologies Corporation). The objective is to acquire vertical profiles of elastic backscatter (distributions of aerosols and clouds, cloud particle phase) at dual-wavelength frequencies from a nadir-viewing geometry during the day and night phases of the orbit.
CALIOP consists of a laser transmitter subsystem, a receiver subsystem, and the payload controller (PLC) subsystem. The laser transmitter subsystem consists of two redundant lasers, each with a beam expander, and a beam steering system ensuring alignment between the transmitter and receiver. The Q-switched Nd:YAG lasers use a crossed porro prism resonator design to minimize alignment sensitivity and polarization outcoupling to provide a highly polarized output beam. Frequency doubling produces simultaneous pulses at 1064 nm and at 532 nm. Each laser produces 110 mJ of energy at each of the two wavelengths at a pulse repetition rate of 20.16 Hz, although only one laser is operated at a time. Beam expanders reduce the angular divergence of the laser beam to produce a footprint of 70 m diameter on the Earth's surface.
Figure 10: Photo of the CALIOP instrument (image credit: BATC, NASA)
Figure 11: CALIOP transmitter and receiver subsystems (image credit: NASA/LaRC)
Two orthogonal polarization components (parallel and perpendicular to the polarization plane of the transmitted beam) are measured at 532 nm. Vertical profiles are measured from the surface to 40 km with the 532 nm channel, with the upper region used for normalization/calibration. The other two channels span 0 to +26 km, covering the cloud and aerosol measurement region with polar stratospheric clouds occurring toward the top of the range. The maximum vertical resolution is 30 m, the footprint diameter on the ground is 70 m. The horizontal spacing between footprint centers is 333 m (along-track). Low altitude data are being downlinked at full resolution. At altitudes above 5 km, resolutions are reduced by on-board averaging. 25) 26) 27) 28) 29) 30)
Table 1: Parameters of the CALIOP instrument
Figure 12: Simplified block diagram of the CALIOP instrument (image credit: NASA/LaRC)
Calibration: CALIOP is calibrated in three steps.
• First, the 532 nm parallel channel signal is calibrated to the predicted molecular volume backscatter coefficient in the 30-34 km region. The molecular backscatter coefficient can be accurately estimated using temperature and pressure profiles from a gridded meteorological analysis product. The 30-34 km region was chosen as the aerosol backscatter in that region is insignificant with respect to molecular backscatter and the molecular density does not exhibit large variations. The parallel-polarized component of the molecular backscatter is derived from the estimate of total molecular backscatter by taking into account the bandwidth of the receiver optical filters. Independent estimates of the 532 nm parallel channel calibration constant are computed at approximately 700 km intervals over the dark side of each orbit and interpolated to the day side.
• Second, the calibration of the 532-nm parallel channel is transferred to the perpendicular channel via insertion of a pseudo-depolarizer in the receiver optical path upstream from the polarization beamsplitter (Figure 12). The pseudo depolarizer ensures that, regardless of the polarization state of the backscatter incident on the receiver, an equal amount of light is sent to the parallel and perpendicular channels of the receiver downstream of the depolarizer. The pseudo depolarizer will be inserted periodically during the mission, to track any relative change in sensitivity of the parallel and perpendicular channel detectors.
• Third, the calibration of the 532 nm channels is transferred to the 1064 nm channel via comparison of the return signals from high-altitude cirrus clouds. Cirrus cloud particles are large compared to the transmitted wavelengths, so the backscatter coefficients will be nearly equal at 532 nm and 1064 nm. By choosing clouds for which the ratio of particulate to molecular scattering is 50 and above, the calibration can be transferred with high accuracy. This calibration can be performed on both the dark and daylight side of the orbit, wherever cirrus of sufficient backscatter strength exist.
Figure 13: View of the instrument locations on CALIPSO (image credit: NASA)
IIR (Imaging Infrared Radiometer):
IIR is provided by CNES and developed at EADS Sodern, France. The objective is to measure calibrated radiances at 10.5 and at 12 µm over a 40 km swath (the two wavelengths are chosen to optimize the joint Lidar/IIR retrievals of cirrus emissivity and particle size).
IIR is a nadir-viewing, non-scanning imager having a 64 km x 64 km swath with a pixel size of 1 km. The CALIOP beam is nominally aligned with the center of an IIR image. IIR uses a single microbolometer detector array (uncooled), with a rotating filter wheel providing measurements at three channels in the window region, on either side of the O3 absorption band at 9.6 µm. The central wavelengths (and spectral widths) of the three channels are 8.65 µm (0.9 µm), 10.6 µm (0.6 µm), and 12.05 µm (1.0 µm). These wavelengths were selected to optimize joint CALIOP/IIR retrievals of cirrus cloud emissivity and particle size. 31) 32) 33) 34)
Figure 14: Illustration of the IIR instrument (image credit: EADS Sodern)
Figure 15: Photo of the assembled IIR instrument (image credit: EADS Sodern)
The IIR device is composed of:
• The ISM (Imaging Sensor Module), constituted of an objective (aperture 0.75) optimized in the thermal infrared, a microbolometer detector array, specific electronics, a passive cooler to refrigerate the whole, and some mechanical pieces
• A filter-carrying wheel enabling to insert alternately 3 spectral filter in front of the camera
• A black body to calibrate the camera
• A pointing mirror rotating to sequentially select between the Earthview, the black body and the direction of the cold space (second source for calibration).
Figure 16: Schematic view of the ISM (image credit: CNES)
On-orbit calibration: The calibration procedure requires viewing scenes at two different known temperatures. A cold scene calibration (4 K) is achieved by observing deep space every 8 seconds, while a hot scene calibration (300 K) is performed every 40 seconds using an internal blackbody source.
Table 2: IIR specifications
Note: The IIR instrument is also referred to as CIM-02 (Caméra Infra-rouge Multimission) on the CALIPSO mission. CIM-02 is of CIM-01 heritage flown on the MetOp-01 mission of EUMETSAT (CIM-01 is also referred to as the “IASI Infrared Imager”). CIM02 differs from CIM01 through its optical interface, the objective and the radiator have been re-designed.
Figure 17: Schematic of the IIR instrument (image credit: CNES)
Figure 18: Electronic architecture of the IIR instrument (image credit: CNES)
WFC (Wide-Field Camera):
WFC was built by Ball Aerospace (a modified version of a commercial star camera, CT-633, a pushbroom type device with a CCD detector array of 512 x 512 pixels). The objective is to provide meteorological context and highly accurate spatial registration between the CALIPSO and the Aqua mission. 35) 36)
WFC is a digital CCD camera with a spectral coverage of 620-670 nm (single band) providing images of a 61 km swath with a spatial resolution of 1 km. In a 5 km central band, the spatial resolution is 125 m. Although the WFC comes with a 512 x 512 CCD array, it essentially operates in the pushbroom line array fashion by reading out only one row of pixels per image frame. Nominally, 488 of the 512 pixels in the target row are being utilized. To minimize smearing effects during readout operations, most of the CCD array is masked off except about 30 rows near the center.
The source data rate is 26 kbit/s. The WFC imagery is also being used to assess the cloud fraction within 1 km IIR pixels to enhance the retrieval of cloud properties from the IIR data.
Table 3: Performance specifications of WFC
Figure 19: Schematic of the WFC instrument (image credit: CNES)
Figure 20: Illustration of the WFC imager (image credit: BATC)
Figure 21: View of WFC swath in relation to laser footprint (image credit: NASA/LaRC)
The CALIPSO ground segment is comprised of two main components:
1) SOGC (Satellite Operations Ground System), consisting of:
• SOCC (Satellite Operations Control Center), located in Toulouse (France)
• TT&C S-band ground stations at Kiruna (Sweden) and Aussaguel (France)
• A digital communication network that provides communication between ground segment components.
2) MOGS (Mission Operations Ground System), dedicated to mission management, detailed payload data processing, payload programming and monitoring and preparation of commands. It consists of:
• The payload data delivery system, including the X-band ground stations located in Alaska (prime), and Hawaii (backup)
• MOCC (Mission Operations Control Center), in Hampton, VA (NASA/LaRC).
Figure 22: Overview of the CALIPSO ground segment (image credit: CNES)
Data and quick-looks of the CALIPSO mission are archived at the NASA/LaRC Atmospheric Sciences Data Center (ASDC). A mirror data site, part of the French ICARE structure, is located in Lille and operated by CNES, CNRS, the University of Lille, and the Région Nord-Pas-de-Calais. 37)
The thematic pole ICARE is managing the production and distribution of the scientific outputs of PARASOL and CALIPSO through its data processing and management center in Lille (CGTD). In the case of CALIPSO, it acts as a mirror site of NASA. In late 2009, the CGTD ICARE was managing the distribution of four TB of data per month, for the benefit of 380 registered users.
1) D. M. Winker, B. A Wielicki, “The PICASSO-CENA Mission,” Part of the EUROPTO Conference on Sensors, Systems and Next Generation Satellites, Proceedings of SPIE, Vol. 3870, Florence, Italy, Sept. 20-24, 1999, pp. 26-36
2) J. Blouvac, B. Lazaed, J. M. Martinuzzi, “CNES Small Satellites Earth Observation Scientific Future Missions, IAA 2nd International Symposium on Small Satellites for Earth Observation, Berlin, April 12-16, 1999, pp. 11-14
3) J. Reagan, D. Winker, “PICASSO-CENA: Combined Active-Passive Sensing from Space,” Proceedings of IGARSS'99, Vol. 1, pp. 240-242
4) D. M. Winker, “Global Observations of Aerosols and Clouds from combined Lidar and passive Instruments to improve Radiation Budget and Climate Studies,” The Earth Observer, Vol. 11, No 3, May/June 1999, pp. 22-25
5) D. Q. Robinson, “PICASSO-CENA Satellite-Based Research Mission: K-12 Education and Public Outreach (Student use of remote sensing for research validation),” Proceedings of the IEEE/IGARSS 2000 Conference, Honolulu, HI, July 24-28, 2000
9) F. Paoli, J. Blouvac, “CALIPSO: A Small Satellite in Low Earth Orbit for the Study of the Clouds and Aerosols,” Proceedings of the IAC 2005, Fukuoda, Japan, Oct. 17-21, 2005, IAC-05-B5.2.02
10) NASA CloudSat-CALIPSO Press Kit, April 2006, URL: http://www.nasa.gov/pdf/147741main_cloudsat-calipso4.pdf
11) Corinne Salcedo, Laurie M. Mann, “CALIPSO and CloudSat Coordinated Ascent Phase to the EOS Afternoon Constellation,” SpaceOps 2006 Conference, Rome, Italy, June 19-23, 2006, paper: AIAA 2006-5759 URL: http://www.ai-solutions.com/Portals/0/AI%20Docs/Technical%20Paper%20Library%20pdf/2006/10.pdf
14) George Hurtt (Chair), Ana Barros, Richard Bevilacqua, Mark Bourassa, Jennifer Comstock, Peter Cornillon, Andrew Dessler, Gary Egbert, Hans-Peter Marshall, Richard Miller, Liz Ritchie, Phil Townsend, Susan Ustin,“NASA Earth Science Senior Review 2011,” June 30, 2011, URL: http://science.nasa.gov/media/medialibrary/2011/07/22/2011-NASA-ESSR-v3-CY-CleanCopy_3x.pdf
15) D. M. Winker, J. Pelon, “The CALIPSO mission,” COSPAR 2010, 38th COSPAR Scientific Assembly, Bremen, Germany, July18-25, 2010, URL: http://www.cnes.fr/automne_modules_files/standard/public/p8628_67f2ab5f07f7-bb51f0fb15f9ad97615319_Atmosphere.pdf
17) Steven A. Ackerman (chair), Richard Bevilacqua, Bill Brune, Bill Gail, Dennis Hartmann, George Hurtt, Linwood Jones, Barry Gross, John Kimball, Liz Ritchie, CK Shum, Beata Csatho, William Rose, Carlos Del Castillo, Cheryl Yuhas, “NASA Earth Science Senior Review 2009,” URL: http://nasascience.nasa.gov/about-us/science-strategy/senior-reviews/2009SeniorReviewSciencePanelReportFINAL.pdf
18) Debra Werner, “NASA Budget fpr Earth Science Lags Behind Rising Expectations,” Space News, January 4, 2010, p. 1 & 4
19) Christophe Maréchal, Nadège Quéruel, David G. Macdonnell, Carolus A. Verhappen, Patricia L. Lucker, “ Flying in a spacecraft constellation: a coordination puzzle,” Proceedings of the SpaceOps 2010 Conference, Huntsville, ALA, USA, April 25-30, 2010, paper: AIAA 2010-2254
20) “CALIPSO Makes Successful Switch to Backup Laser, Keeping Important Data Stream Alive,” NASA, April 16, 2009, URL: http://www.nasa.gov/topics/earth/features/calipso-laserswitch.html
23) J. Blouvac, F. Paoli, P. Landiech, P. Castillan, “CALIPSO Small Satellite Flight Commissioning,” Proceedings of the 57th IAC/IAF/IAA (International Astronautical Congress), Valencia, Spain, Oct. 2-6, 2006, IAC-06-B5.4.09
24) D. M. Winker, J. Pelon, J. A. Coakley Jr., S. A. Ackerma n, R. J. Charlson, P. R. Colarco, P. Flama nt, Q. Fu, R. M. Hoff , C. Kittaka, T. L. Kubar, H. Le Treut, M. P. Mcc ormi ck, G. Mégie, L. Poole, K. Powell, C. Trepte, M. A. Vaughan, B. A. Wielicki, “The CALIPSO Missio n - A Global 3D View of Aerosols and Clouds,” BAMS (Bulletin of the American Meteorological Society), Vol. 91, Issue 9, Sept. 2010, pp. 1211-1229, URL: http://journals.ametsoc.org/doi/pdf/10.1175/2010BAMS3009.1
25) David Winker, William Hunt, Carl Weimer, “The On-Orbit Performance of the CALIOP Lidar on CALIPSO,” Proceedings of the 7th ICSO (International Conference on Space Optics) 2008, Toulouse, France, Oct. 14-17, 2008, URL: http://www.icsoconference2008.com/cd/pdf/S15%20-%20Lidars%20-%20Hunt.pdf
26) D. Winker, C. Hostetler, W. Hunt, “ CALIOP: The CALIPSO Lidar,” Proceedings of 22nd ILRC (International Laser Radar Conference), Matera, Italy, July 12-16, 2004, ESA SP-561, Vol. II, pp. 941-944
27) L. R. Poole, D. M. Winker, J. R. Pelon, M. P. McCormick, “CALIPSO: Global aerosol and cloud observations from lidar and passive instruments,” Proceedings of SPIE, Vol. 4881, 9th International Symposium on Remote Sensing, Aghia Pelagia, Crete, Greece, Sept. 23-27, 2002
29) D. M. Winker, W. Hunt, C. Hostetler, “Status and performance of the CALIOP lidar,” Proceedings of SPIE, Vol. 5575, 2004, pp. 8-15, URL: http://www-calipso.larc.nasa.gov/resources/pdfs/SPIE_5575-3.pdf
30) D. Winker, “CALIPSO,” Nov. 15, 2004, TWP-ICE Planning Meeting, Darwin, Australia, URL: http://www.bom.gov.au/bmrc/wefor/research/twpice/Darwin_Nov-2004_meeting/S1/S1_WinkerTWPICE_CALIPSO.pdf
34) IIR brochure of EADS Sodern, URL: http://www.sodern.com/sites/docs_wsw/RUB_160/FICHE_IIR.pdf
35) C. Weimar, R. Schwiesow, M. LaPole, “CALIPSO: lidar and wide-field camera performance,” Proceedings of SPIE, `Earth Observing Systems IX,' Edited by W. L. Barnes, J. J. Butler, Vol. 5542, 2004, pp. 74-85
36) M. C. Pitts, Y. Hu, J. C. Currey, D. Winker, J. D. Lambeth, “CALIPSO Algorithm Theoretical Basis Document Wide Field Camera (WFC) Level 1 Algorithms,” Oct. 25, 2005, URL: http://www-calipso.larc.nasa.gov/resources/pdfs/WFC_Level1_baseline_v1.0.pdf
37) “CALIPSO Data User's Guide,” Oct. 4, 2010, NASA/LaRC, URL: http://www-calipso.larc.nasa.gov/resources/calipso_users_guide/
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.