CALIPSO will carry the first polarization lidar in orbit, along with infrared and visible passive imagers, and will fly in formation as part of the Afternoon Constellation (A-train). The acquisition of observations which are simultaneous and coincident with observations from other instruments of the A-train will allow numerous synergies to be realized from combining CALIPSO observations with observations from other platforms. In particular, cloud observations from the CALIPSO lidar and the CloudSat radar will complement each other, together encompassing the variety of clouds found in the atmosphere, from thin cirrus to deep convective clouds. CALIPSO has been developed within the framework of a collaboration between NASA and CNES and is currently scheduled to launch, along with the CloudSat satellite, in spring 2006. This paper will present an overview of the CALIPSO mission, including initial results

McCormick, M. Patrick

Pelon, Jacques

Winker, David M.

NASA Technical Reports Server

INITIAL RESULTS FROM CALIPSO 
David M Winker(1), Jacques Pelon(2), and M. Patrick McCormick(3) 
(1)NASA Langley Research Ctr, MS/475, Hampton, Virginia  23681, USA, E-mail: david.m.winker@nasa.gov 
(2)Universite Pierre et Marie Curie, 4 Place Jussieu, Paris, France, E-mail : jacques.pelon@aero.jussieu.fr 
(3)Hampton University, Hampton, Virginia, USA, E-mail: pat.mccormick@hamptonu.edu 
 
ABSTRACT 
CALIPSO will carry the first polarization lidar in orbit, 
along with infrared and visible passive imagers, and will 
fly in formation as part of the Afternoon Constellation 
(A-train).  The acquisition of observations which are 
simultaneous and coincident with observations from 
other instruments of the A-train will allow numerous 
synergies to be realized from combining CALIPSO 
observations with observations from other platforms.  In 
particular, cloud observations from the CALIPSO lidar 
and the CloudSat radar will complement each other, 
together encompassing the variety of clouds found in 
the atmosphere, from thin cirrus to deep convective 
clouds.  CALIPSO has been developed within the 
framework of a collaboration between NASA and 
CNES and is currently scheduled to launch, along with 
the CloudSat satellite, in spring 2006.  This paper will 
present an overview of the CALIPSO mission, including 
initial results. 
 
Fig. 1.  The CALIPSO satellite. 
 
1. INTRODUCTION 
The Cloud-Aerosol Lidar and Infrared Pathfinder 
Satellite Observations (CALIPSO) satellite has been 
developed as a collaboration between NASA and the 
French Space Agency CNES [1].  CALIPSO will be 
flown as part of the Afternoon constellation, including 
also the Aqua, CloudSat, Aura, and PARASOL 
satellites.  CALIPSO and the rest of the formation will 
fly at an altitude of 705 km and an inclination of 98o. 
The primary objective of CALIPSO’s 3-year mission is 
to provide the observations necessary to improve our 
understanding of the effects of clouds and aerosols on 
the climate system.  The CALIPSO payload includes 
three instruments:  (1) the Cloud-Aerosol LIdar with 
Orthogonal Polarization (CALIOP, pronounced the 
same as “calliope”) to provide vertical profiles of 
aerosol and cloud backscatter and depolarization; (2) an 
Imaging Infrared Radiometer (IIR) with three channels 
in the infrared window region optimized for retrievals of 
cirrus particle size; and (3) the Wide Field Camera 
(WFC), a moderate spatial resolution imager with one 
visible channel.  WFC images provide meteorological 
context and are also incorporated into IIR retrievals of 
cloud properties.  The CALIPSO payload was built by 
the Ball Aerospace and Technology Corporation 
(BATC) in Boulder, Colorado, except for the IIR which 
was provided by CNES.  CALIPSO utilizes a 
PROTEUS spacecraft bus, developed by CNES and 
Alcatel. 
 
2. INSTRUMENTS 
The physical layout of the payload is shown in Fig. 2, 
with key instrument characteristics listed in Table 1.  A 
diode-pumped Nd:YAG laser produces linearly-
polarized pulses of light at 1064 nm and 532 nm. The 
atmospheric returns are collected by a 1-meter telescope 
which feeds a three-channel receiver measuring the 
backscattered intensity at 1064 nm and the two 
orthogonal polarization components at 532 nm  (parallel 
and perpendicular to the polarization plane of the 
transmitted beam).  
 
The receiver sub-system consists of the telescope, relay 
optics, detectors, preamps, and line drivers mounted on 
a stable optical bench. A mechanism located in the 
collimated portion of the beam contains a shutter and a 
depolarizer used in calibrating the 532 nm perpendicular 
channel.  A narrowband etalon is used in the 532 nm 
channel to reduce the solar background illumination.  A 
dielectric interference filter provides sufficient solar 
rejection for the 1064 nm channel.  Dual digitizers on 
each channel provide the effective 22-bit dynamic range  
https://ntrs.nasa.gov/search.jsp?R=20060027795 2019-08-29T22:07:33+00:00Z
 2
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 2.  The CALIPSO payload. 
 
 
Table 1.  CALIPSO Payload Characteristics 
CALIOP 
Laser: 
  pulse energy 
 
  polarization purity 
  pulse rate 
Receiver: 
   telescope diameter   
   channels, passband 
  
 
footprint 
sampling  resolution: 
 
 
 
532 nm:   110 mJ 
1064 nm: 110 mJ 
99.9% (532 nm) 
20.16 Hz 
 
1 meter 
532 nm ⏐⏐,  37 pm 
532  nm  ⊥, 37 pm 
1064 nm total, 450 pm 
90 m  
30-60 m vertical 
333 m horizontal 
WFC 
  wavelength 
  spectral bandwidth 
  IFOV/swath 
 
645 nm 
50 nm 
125 m/ 61 km 
IIR 
  wavelengths 
  spectral resolution 
  IFOV/swath 
 
8.65 μm,10.6 μm,12.0μm 
0.6 μm – 1.0 μm 
1 km/64 km 
 
needed to measure both cloud and molecular backscatter 
signals. An active beamsteering system is used to ensure 
alignment between the transmitter and the receiver. 
 
The laser transmitter subsystem consists of two 
redundant lasers, each with a beam expander, and the 
beamsteering system. The Nd:YAG lasers are Q-
switched and frequency-doubled to produce 
simultaneous pulses at 1064 nm and 532 nm.  Only one 
laser is operated at a time.  Beam expanders reduce the 
angular divergence of the laser beam to produce a beam 
diameter of about 90 meters at the Earth’s surface.  The 
lasers are passively cooled using a dedicated thermal 
radiator panel. Each laser is housed in its own sealed 
canister filled with dry air at slightly more than standard 
atmospheric pressure. 
 
The fundamental sampling resolution of the lidar is 30 
meters vertical and 333 meters horizontal, determined 
by the receiver electrical bandwidth and the laser pulse 
repetition rate.  Backscatter data will be acquired from 
the surface to 40 km with 30 m vertical resolution.  Low 
altitude data will be downlinked at full resolution. To 
reduce the required telemetry bandwidth, data from 
higher altitudes will be averaged on board both 
vertically and horizontally to reduce the data rate (Table 
2).  The lidar is calibrated by normalizing the return 
signal between 30 km and 34 km.  A depolarizer can be 
inserted into the 532 nm beampath to calibrate the 
perpendicular channel relative to the parallel channel.  
The 1064 nm channel is calibrated relative to the 532 
nm total backscatter signal using cirrus clouds as 
targets.  Additional detail on CALIOP can be found in 
[2]. 
 
Table 2.  Spatial resolution of downlinked data. 
Vertical Resolution (m) Altitude 
Range (km) 
Horizontal 
Resolution (km) 532 nm 1064 nm 
30.1 to 40.0  5.0 300 --- 
20.2 to 30.1 1.67 180 180 
8.2 to 20.2 1.0 60 60 
-0.5 to 8.2 0.33 30 60 
-2.0 to –0.5 0.33 300 300 
 
 
The CALIPSO payload also contains two passive 
instruments: the Imaging Infrared Radiometer (IIR) and 
the Wide Field Camera (WFC), which are both nadir-
viewing and co-aligned with the lidar.  The IIR provides 
calibrated radiances at 8.65 μm, 10.6 μm, and 12.05 μm 
over a 64 km swath.  These wavelengths were chosen to 
optimize joint lidar/IIR retrievals of cirrus emissivity 
and particle size.  The IIR is built around an Infrared 
Sensor Module, developed for the IASI instrument.  Use 
of a microbolometer detector array in a non-scanning, 
staring configuration allows a simple and compact 
design.  A rotating filter wheel provides wavelength 
selection.  The IIR instrument is provided by CNES 
with algorithm development performed by the Institute 
Pierre Simon Laplace (Paris).  The WFC is a modified 
Ball star tracker camera, with a single channel covering 
the 620 nm to 670 nm spectral region providing images 
of a 61 km swath with spatial resolution of 125 meters.  
 Lidar 
Telescope
Wide-Field 
Camera
Imaging Infrared 
Radiometer 
 Laser 
Transmitter 
Subsystem 
 3
3. RETRIEVALS AND DATA PRODUCTS 
Aerosol and cloud layers are detected using an adaptive 
threshold technique [3].  Aerosols are then 
discriminated from clouds using the magnitude and 
spectral behavior of the lidar return signals [4] and 
extinction profiles are retrieved using a linear iterative 
technique [5].  These algorithms are implemented in a 
unique analysis scheme that employs a nested, multi-
scale averaging approach designed to optimize tradeoffs 
between spatial resolution and signal-to-noise ratio 
(SNR) [6].   
 
Because the magnitude of the lidar return signal varies 
by several orders of magnitude, depending on the 
contents of the atmospheric column, the SNR of a single 
backscatter profile can vary enormously.  Strong clouds 
can be detected in single-shot profiles, but the detection 
and analysis of weak aerosol layers requires significant 
horizontal and vertical averaging.  If the lidar return 
signals are analyzed at a uniform high spatial resolution, 
many weak features will be missed and retrievals may 
be very noisy.  If the data is averaged to a uniform low 
spatial resolution, strong cloud returns may be averaged 
together with weaker aerosol signals.  Because of the 
nonlinear processes involved, retrievals on the averaged 
signals will be biased and will give biased estimates of 
radiative effects. 
 
Three types of CALIOP Level 2 data products are 
produced: a vertical feature mask (VFM), which 
provides a vertical mapping of the locations of aerosol 
and cloud layers along with layer type information ; 
layer products, which provide layer-integrated 
properties of aerosol and cloud layers; and separate 
aerosol and cloud profile products providing profiles of 
particulate backscatter and extinction.  Further details 
on CALIOP retrieval algorithms and data products are 
given in [6].   
 
The IIR retrieval algorithms are focused on retrieving the 
emissivity and effective particle size of ice clouds.  Lidar 
cloud heights will be used in IIR retrievals to provide an 
independent estimate of cloud temperature, to identify 
single- and multi-layer cloud, and to provide improved 
identification of cloud-free scenes.  Under daylight 
conditions, WFC data is also used in the algorithm.  Two 
types of Level 2 IIR data products are produced.  A 
Track Product contains retrievals only for IIR pixels 
coincident with lidar footprints.  A Swath Product 
contains data retrieved from across the 64 km swath of 
the IIR. 
 
Level 1 and Level 2 data products are summarized in 
Table 3.  Level 1 products are all geolocated, time-
referenced and radiometrically calibrated.  Further 
information is available in the CALIPSO Data Products 
Catalog, available from the CALIPSO web site.  
Processing and archival of data from all the CALIPSO 
instruments will be performed at the NASA Langley 
Research Center Atmospheric Sciences Data Center 
(ASDC).  In accordance with NASA data policy, 
CALIPSO data will be freely available after validation.   
 
Table 3.  CALIPSO Data Products. 
CALIOP Profiles of 532 nm/1064 nm total attenuated backscatter and 532 nm perpendicular 
attenuated backscatter 
IIR Calibrated radiances 
Level 1 
WFC Calibrated radiances, reflectances 
Cloud/Aerosol Layer Product:   
     Cloud layer heights, thickness, optical depth, ice/water phase at 1/3, 1, and 5 km 
     Aerosol layer heights, thickness, optical depth and  type at 5 km 
Aerosol Profile Product: aerosol extinction and attenuation-corrected backscatter at 40 km 
Cloud Profile Product: cloud extinction and attenuation-corrected backscatter at 5 km  
CALIOP 
Vertical Mask - cloud/aerosol ID and type 
Track product - cloud emissivity and effective particle size along satellite ground track 
Level 2 
IIR 
Swath Product - cloud emissivity and effective particle size across IIR swath 
 
4. OBSERVING STRATEGY 
CALIPSO will fly in formation with the EOS Aqua 
satellite as part of the Aqua constellation.  The Aqua 
satellite was launched in May 2002 and the Aura and 
PARASOL satellites were launched in 2004. The launch 
of CALIPSO and CloudSat will complete the 
constellation of 5 satellites.  The CALIPSO orbit will be 
controlled to provide space-time coincidence with 
 4
observations from the other satellites of the 
constellation.  The satellites of the constellation fly in a 
sun-synchronous 705-km circular orbit with a 98o orbit 
inclination.  The Aqua orbit is controlled to maintain an 
ascending node equatorial crossing time of 13:30 local 
time.  The CALIPSO orbit will be maintained relative to 
Aqua so that a point on the ground will be observed by 
the two platforms with an average time separation of 1.5 
minutes.    This timing constraint ensures that clouds 
observed by the two platforms will not have time to 
evolve significantly between the two observations. 
Based on experience with the JASON satellite, which 
uses the same PROTEUS spacecraft bus as CALIPSO, 
satellite pointing can be controlled to within 300 meters.  
Correlation of WFC and MODIS imagery will allow 
spatial co-registration of the two data sets to better than 
100 m, if necessary, during the day. The CloudSat 
satellite will fly in formation with the CALIPSO 
satellite, at an average separation of about 12 seconds.  
The CloudSat orbit will be controlled to keep the 
footprint of CALIOP within the footprint of the 
CloudSat radar (approximately 1.4 km wide) to provide 
coincident radar and lidar observations of clouds. 
 
5. VALIDATION 
Validation of CALIPSO data products via 
intercomparisons with independent measurements is 
essential to the production of a high quality dataset.  A 
variety of validation activities are planned, including 
aircraft underflights and measurements from ground-
based instruments.  Data from ground-based networks 
such as Aeronet, MPLNet, AD-Net and EARLINET are 
considered critical to the validation of CALIPSO data.  
Validation flights with airborne lidars on board the 
NASA ER-2 and King Air aircraft soon after the 
commencement of payload operations are planned to 
provide early validation of Level 1 data products.  The 
CALIPSO team will also participate in field campaigns 
focused on cloud and aerosol measurements, which 
provide comparison datasets which are more 
comprehensive than otherwise available. 
 
6. SCHEDULE 
CALIPSO will be launched by a Delta-II launch vehicle 
in a dual-payload configuration with the CloudSat 
satellite.  The integrated CALIPSO satellite was shipped 
to the launch site, Vandenburg AFB, in May 2005.  
End-to-end atmospheric tests were conducted in 
December 2003 in Boulder, CO, at the completion of 
payload integration, and in June 2005 at Vandenburg.  
Launch was scheduled for October 2005, however, a 
labor strike and concerns over the flight readiness of the 
Delta-II resulted in a delay.  Launch is now scheduled 
for spring 2006 and data products should become 
available by the end of 2006. 
REFERENCES 
1.   Winker, D. M., J. Pelon, and M. P. McCormick, 
“The CALIPSO mission: Spaceborne lidar for 
observation of aerosols and clouds,” Proc. SPIE,  
4893, 1-11 (2003). 
2.   Winker, D. M., W. H. Hunt, and C. A. Hostetler, 
“Status and Performance of the CALIOP lidar,” 
Proc. SPIE, 5575, 8-15 (2004). 
3.  Winker, D. M., and M. A. Vaughan, “Vertical 
distribution of clouds over Hampton, Virginia 
observed by lidar under the ECLIPS and FIRE ETO 
programs”, Atmos. Res. 34,  117-133 (1994). 
4.  Liu, Z., M. A. Vaughan, D. M. Winker, C. A. 
Hostetler, L. R. Poole, D. L. Hlavka, W. D. Hart 
and M. J. McGill, “Use of Probability Distribution 
Functions for Discriminating Between Cloud and 
Aerosol in Lidar Backscatter Data”, J. Geophys. 
Res. doi:10.1029/2004JD004732 
5. Elterman, L., “Aerosol measurements in the 
troposphere and stratosphere”, Appl. Opt. 5, 1769-
1776 (1966). 
6.   Vaughan, M. A., S. A. Young, D. M. Winker, K. A. 
Powell, A. H. Omar, Z. Liu, Y. Hu, and C. A. 
Hostetler, “Fully automated analysis of space-based 
lidar data: An overview of the CALIPSO retrieval 
algorithms and data products,” Proc. SPIE 5575, 
16-30 (2004). 
 
 


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