A NASA/CSA (USA/Canada) cooperative research mission in the ESSP (Earth System Science Pathfinder) program to study the effects of clouds on climate and weather. CloudSat's primary goal is to furnish data needed to evaluate and improve the way clouds are represented in global models, thereby contributing to better predictions of clouds and thus to their poorly understood role in climate change and the cloud-climate feedback [focused on understanding the role of optically thick clouds on the Earth's radiation budget (a balance of solar energy reaching the Earth and lost to space that ultimately controls the temperature of the Earth)]. 1) 2) 3) 4) 5) 6) 7) 8) 9)
Although the original CloudSat concept included the combination of lidar and radar and even precipitation measurements (GEWEX 1994), this proved too costly. Also due to cost constraints imposed by ESSP, contributions to specific portions of the mission were required.
In the cooperative arrangement, NASA provides the spacecraft (RS2000, a variant of the BCP 2000 bus of BATC), major portions of the cloud-profiling radar including integration and test of the radar system, and the S/C launch, while CSA (Canadian Space Agency) provides additional components of the advanced cloud-profiling radar. Other partners in the program are: CIRA (Cooperative Institute for Research in the Atmosphere) of CSU (Colorado State University) at Fort Collins, CO handles data processing and distribution during the mission operations phase (archiving after the mission will be the responsibility of a NASA DAAC); ground operations and communications are provided the USAF/STP (Space Test Program), and the U.S. Department of Energy (DOE) provides ground and aircraft-based observations for validation. In addition, members of the Science Team, including non-USA members, are contributing additional ground and aircraft-based measurements for validation. The CloudSat mission and payload development is managed by NASA/JPL (Figure 5).
CloudSat fills a significant gap in the existing and planned Earth observation missions by measuring the vertical profile of clouds using active remote sensing (94 GHz radar). The CloudSat S/C flies on-orbit in tight formation with a NASA/CNES lidar satellite CALIPSO, which carries a dual-wavelength backscattering (polarization-sensitive) lidar. The CloudSat orbit will be adjusted to hold a fixed distance of about 460 km (about 60 s delay) with respect to CALIPSO, with an option to decrease this distance to a 15 second separation. The sensors of both S/C point into the same ground track. The footprint of the radar is expected to overlay the footprint of the lidar by about 50%, or more, of the time and will always be within 2 km. It is planned that the two satellites fly in formation with the Aqua S/C (EOS-PM) such that the radar and lidar footprints will always fall in the central 36 km of the Aqua-MODIS swath.
The CloudSat S/C, built by BATC (Ball Aerospace & Technology Corporation), uses a BCP 2000 series bus of QuikSCAT and ICESat heritage (also referred to as RS 2000 bus). The S/C is three-axis inertially stabilized (momentum biased), the ADCS (Attitude Determination and Control Subsystem) uses a star tracker (one redundant) and 14 coarse sun sensors, which also provide sun direction for solar array control, and three two-axis magnetometers. Actuation is provided by 3 dual-winding torque rods and 4 reaction wheels. The pointing accuracy is ≤ 0.07º, two-axes, 99.7% probable; the geolocation knowledge of the radar footprint position is better than 1 km on the geoid, two-axes, 99.7% probable. Two global positioning system receivers (C/A code capability) provide GPS time and position and velocity to the onboard location determination process.
Figure 1: Artist's rendition of the CloudSat spacecraft (image credit: NASA)
The S/C wet mass is about 995 kg, the S/C power is 700 W average (> 800 W peak), a battery capacity of 40 Ah is provided for eclipse operations. The main structure has a size of 2.54 m x 2.03 m x 2.29 m. The wing span of the deployed solar array is 5.08 m from tip to tip (total array area of 6.4 m2). The design life of both, the spacecraft and radar, exceeds two years, and consumables are carried for a three-year mission, enabling an extended mission. 10)
Propulsion: The spacecraft uses an all-welded, chemical, blow-down monopropellant system for attitude control and translational maneuvers. The propellant is hydrazine and the pressurant is gaseous nitrogen. There are four thruster assemblies, each rated at 4.45 N (newton) with an Isp of 220 seconds. Other propulsion system components include the fill/drain valve, fill/vent valve, pressure transducer and two latching isolation valves.
Launch: A launch of CloudSat on a Delta 7420-10C launch vehicle from VAFB, CA took place on April 28, 2006. CloudSat was co-manifested with the NASA lidar mission CALIPSO (formerly named ESSP-3). 11)
Orbit: Sun-synchronous near-circular “frozen” orbit [same orbit as Aqua (EOS/PM)], altitude = 705 km, inclination = 98.2º.
RF communications: CloudSat is being monitoring and controlled from a USAF facility using the Air Force Satellite Control Network (AFSCN). The payload data is downlinked in S-band at 1 Mbit/s and relayed to the control center, where it is sent to CIRA for processing into data products. 12)
Formation flying: CloudSat is going to be part of the A-train (Aqua in the lead and Aura at the tail), consisting of the following S/C sequence: Aqua, CloudSat, CALIPSO, PARASOL, and Aura. Formation flying is a navigation strategy that enables CloudSat to closely track the groundtracks of the lidar spacecraft CALIPSO and Aqua in a very precise way. After launch, maneuvers within the first 45 days of the mission will bring the CloudSat spacecraft into formation with the other two spacecraft. The CloudSat orbit will be adjusted and monitored to hold the CloudSat spacecraft at a fixed distance/time from CALIPSO. CloudSat is to trail Aqua by ≤ 120 s and will maneuver to just 15 s ahead of CALIPSO. CloudSat will then maintain a tight formation with CALIPSO by controlling its cross-track motion to within ±1 km of the CALIPSO ground track. This is achieved by placing CloudSat in a small circulation orbit relative to CALIPSO and contained within CALIPSO's control box. The chosen delay is a compromise between the desire to minimize the time delay between the radar and lidar measurements and the need to hold the frequency of formation flying maintenance maneuvers to an interval of once per week or longer. In this way, the radar footprint will spatially overlay the lidar footprint much of the time, creating coordinated and essentially simultaneous measurements. The mean separation time of CloudSat from CALIPSO is 15 seconds. 13) 14)
The addition of the CloudSat and CALIPSO satellites into the constellation, and the controlled maintenance of this formation of satellites, brings the opportunity of combining active (the CloudSat radar and the CALIPSO lidar) with the more traditional passive measurement approaches and Aqua, Aura and PARASOL.
Figure 2: Illustration of the A-train formation flight configuration (image credit: NASA)
Figure 3: Alternate view of CloudSat (image credit: Ball Aerospace)
Figure 4: Line drawing of the CloudSat spacecraft (image credit: NASA)
• The CloudSat spacecraft and its payload are operating nominally during the sunlit portion of the orbit in 2014.
• December 11, 2013: CloudSat successfully executed an 'Orbit Lower Maneuver' on 6 December, 2013. The spacecraft is well positioned in it's constellation control box and is in good ground track alignment with CALIPSO. It is expected that this was the last maneuver of 2013, baring any unexpected atmospheric behavior. 15)
• June 2013: The 2013 Senior Review evaluated 13 NASA satellite missions in extended operations: ACRIMSAT, Aqua, Aura, CALIPSO, CloudSat, EO-1, GRACE, Jason-1, OSTM, QuikSCAT, SORCE, Terra, and TRMM. The Senior Review was tasked with reviewing proposals submitted by each mission team for extended operations and funding for FY14-FY15, and FY16-FY17. Since CloudSat, GRACE, QuikSCAT and SORCE have shown evidence of aging issues, they received baseline funding for extension through 2015. 16)
- Continuing the CloudSat mission carries a number of benefits: 1) allowing for new science in the context of weather and climate variability and also enabling new products, 2) uninterrupted applications to aviation and weather forecasting, 3) improved understanding of seasonal and inter-annual variations in cloud behavior, 4) enhanced data for evaluating model behavior, and 5) providing calibration for future missions such as EarthCARE (2016) and GPM (2014). There is also strong synergy with the future OCO-2 mission as the oxygen A-band from OCO-2 provides complementary information on clouds.
• May 2013: Despite a serious battery anomaly (in April 2011), CloudSat has returned to normal operations and has also rejoined the A-Train. The team had to extensively modify the method of operations, including the plans for performing burns. On-orbit data has demonstrated a robust system that is capable of maintaining formation relative to CALIPSO. CloudSat expects to be operational for many additional years – the remaining fuel onboard the vehicle should last for approximately another 7 years, and no other components on the spacecraft have shown any measurable degradation. 17)
• On July 24, 2012, the CloudSat spacecraft successfully executed the first Drag Make-Up (DMU) maneuver, since returning to the A-Train. This 12.5 cm/s maneuver successfully adjusted the position of the spacecraft within it's control box and aligned the ground track for formation flying with Calipso [Ref. 18) Update of July 26, 2012] .
• On July 17, 2012, the CloudSat spacecraft successfully executed an “Inclination Increase Maneuver”. The results indicate very small underperformance, which will be corrected by a DMU (Drag Make Up) maneuver on 25 July. Last night's maneuver successfully positioned the CloudSat spacecraft 108 seconds behind CALIPSO and in alignment with the other A-Train (Afternoon Constellation) satellites. This completes the maneuver campaign to return CloudSat to the A-Train (update of July 19, 2012, Ref. 23).
• The CloudSat spacecraft returned to the A-Train with an orbit raise maneuver on May 15, 2012. CloudSat is now in a position about 100 seconds behind CALIPSO. An inclination-increase maneuver will be performed in mid-July to achieve footprint overlap between CALIPSO's lidar and CloudSat's radar instruments. 19) 20)
• In January 2012, CloudSat continues to fully operate in the mode (DO-OP) and all issues with the SSR (Solid State Recorder) operation have been resolved. CloudSat plans on rejoining the A-Train constellation orbit beginning February 3, 2012 to be completed by the end of February (Ref. 23): update for January 23, 2012).
• In November 2011, NASA/JPL declared CloudSat fully operational in the DO-OP (Daylight-Only Operation) mode per the revised CONOPS. The spacecraft cycles its subsystems on and off in Sun and eclipse portions of the orbit via weekly command sequences from the RSC. CloudSat is collecting science data during the sunlit portions of the orbit, below the A-Train, and hibernates in a stable spin during eclipse, to recover and return to point at the sun as it emerges from the dark side of the Earth. 21)
• This new CONOPS (Concept of Operations) requires constant care and monitoring of the thermal and power profiles, as well as more intensive commanding for the CloudSat operators. Though CloudSat will never be a fully nominal mission again, it is collecting data for 54 out of the 65 sunlit minutes in its orbit, and the CIRA (Cooperative Institute for Research in the Atmosphere) has begun distribution of science data to the CloudSat community once again. DO-OP is in use today, and maneuvers are currently being executed to return CloudSat to the A-Train, where it will fly 88 along-track seconds behind CALIPSO and resume its role in the A-Train constellation (Ref. 21).
• On Oct. 7, 2011, CloudSat successfully executed an Orbit Lowering ΔV Maneuver. As planned, telemetry indicated a burn duration of 398.6 s for a ΔV of -1.4 m/s. Attitude control was nominal during the burn. Following the maneuver, the spacecraft successfully transitioned back into point standby mode. Analysis of the post-maneuver orbit, indicates that the spacecraft achieved a ΔV of 1.3965 m/s, lowering the semi-major axis by 2.63 km. The CloudSat team is extremely pleased that this maneuver executed as planned, demonstrating the spacecrafts ability to perform maneuvers in advance of returning to a science orbit for the remainder of the mission. - With this demonstration of maneuverability, the Project had the confidence to recommend to NASA that CloudSat be allowed to return to the A-Train. A plan for this return is in place and currently executing toward completion (Ref. 21).
• In June 2011, the NASA Earth Science Senior Review recommended an extension of the CloudSat mission up to 2015. 22)
• CloudSat is operating nominally in early 2011. However, on April 17, 2011, CloudSat suffered a battery anomaly and has not been transmitting data since then. 23)
Although at about the same altitude, CloudSat is no longer part of the A-train of satellites, and hence no longer has the old 16-day repeating orbit. Orbital elements (the so-called TLE) may be downloaded and used as before and the NASA orbital website is still operational. Eventually, CloudSat may return to the A-Train.
• CloudSat is operating nominally in 2010 (beyond the design life of 2 years). NASA granted a mission extension to the end of 2011. In 2009 the Senior Review Panel recommended to NASA to keep CloudSat operational until the EarthCARE mission comes along in 2013. 24) 25)
CloudSat is beginning to meet its mission objectives: evaluating the representation of clouds in global models; evaluating the energy balance for different cloud systems; evaluating the cloud retrievals of other satellite instruments; improving the understanding of aerosol indirect effects. Its data products are highly relevant to NASA’s mission, especially in the area of the role of clouds in climate. In the short term, CloudSat products are being used to test a wide range of global atmospheric models, leading to improved simulation of clouds and cloud processes. In the longer term, CloudSat’s products could be assimilated into weather prediction models to improve forecasts.
• In June 2009 CPR is currently operating at better than the required performance. 26)
• In 2008, the CloudSat project has received authorization from NASA for an extension of its nominal 22-month mission through FY11. Continuing the mission beyond 22 months will produce many other science benefits and opportunities. 27) 28)
• CloudSat has provided the first real information on the fraction of clouds that produce precipitation. Over the Earth's oceans, CloudSat has shown that precipitation is much more common than was previously thought, due to the fact that precipitation over oceans is extremely hard to measure and that the light rain that often falls has been completely missed by satellite observations until now. CloudSat has shown that almost 15% of all oceanic clouds produce rain that falls to the surface. This is a fraction larger than previously believed and has much significance for improved understanding of the Earth's hydrological cycle. Globally averaged, approximately 12% of all clouds are producing rain. This quantity was unknown previous to CloudSat observations.
• On July 4, 2007 CloudSat executed a maneuver designed to avoid a close approach with the Iranian satellite, SINAH-1. The close approach was predicted to occur on July 6, 2007. Within the A-Train formation, CloudSat maintains a separation of 75 to 112 km with CALIPSO, its nearest neighbor in the constellation. The maneuver on July 4 was similar to the maneuvers CloudSat has conducted every few weeks in order to maintain this formation with CALIPSO. CloudSat conducted another maneuver on July 7, after the conjunction, to reverse the drift caused by the maneuver on July 4 and maintain the formation with CALIPSO.
• With the successful completion of OR2 (orbit raise maneuver no. 2 - segments A & B) on 27 May, 2006, the CloudSat spacecraft is now part of the A-Train constellation.
• The 94 GHz Cloud Profiling Radar (CPR) of the CloudSat mission was successfully transitioned to “operate mode” on May, 20, 2006. Science data have been collected since June 2, 2006.
Figure 5: Overview of CloudSat mission partners (image credit: NASA)
Sensor complement: (CPR)
CPR (Cloud Profiling Radar):
CPR is a 94 GHz nadir-looking millimeter-wave radar that measures the power backscattered by clouds as a function of distance from the radar (clouds are weak scatterers of microwave radiation especially in contrast to the reflection of the underlying Earth's surface - hence, maximum sensitivity of the CPR is required). The overriding requirement on CPR was to achieve a minimum detectable cloud reflectivity factor (Ze) of -28 dBZ.
The design of the CPR consists of the following subsystems: RFES (Radio Frequency Electronics Subsystem), HPA (High Power Amplifier), Antenna Subsystem (Quasi-Optical Transmission Line), and DSS (Digital Subsystem). The RFES consists of an up-converter which generates a pulsed signal and up-converts it to 94 GHz. The signal is amplified to about 200 mW by a state-of-the-art MMIC power amplifier. The receiver portion of the RFES down-converts the signal to an IF (Intermediate Frequency). The IF signal is detected using a logarithmic amplifier (high dynamic range). The receiver noise level is critical in achieving the required sensitivity.
The HPA (High-Power Amplifier), which amplifies the transmitted pulse to a nominal power level of 1.7 kW, consists of an EIK (Extended Interaction Klystron) and a high-voltage power supply (HVPS). Both a primary and a backup HPA are used to enhance system reliability. EIK differs from standard klystrons by using resonated bi-periodic ladder lines as a replacement for conventional klystron cavities. The HVPS provides 20 kV needed to operate the EIK and provides telemetry data necessary to system needs. The design uses a boost supply to minimize input current transients during the pulsing period and control EMC problems. Both the 94-GHz EIK and the 20-kV HVPS on CloudSat are the first of their kinds being flown in space. The EIK tube is manufactured by Communications and Power Industries, Canada, Inc.
Figure 6: The CPR assembly with a schematic of the antenna and HPA subsystems (image credit: NASA)
Note: The inset figures of Figure 6 are actual photographs of flight hardware.
The CPR antenna is a fixed 1.85 m diameter reflector of composite graphite material to reduce mass. The antenna provides ≥ 63.1 dBi gain, has a half-beamwidth of ≤ 12º, and has sidelobes < about -50 dB for angles ≥ 7º from boresight. The quasi-optical transmission line (QOTL) replaces the conventional waveguide and circulator for sending power from the HPA to the reflector and sending received power to the receiver subsystem. Waveguides are replaced by mirrors and free-space propagation, while the circulator duplexing function is handled by a polarizer and Faraday rotator. The advantage of the QOTL over conventional waveguide and circulator is reduced loss, important for meeting sensitivity requirements. The DSS provides the command, control, and telemetry interface to the S/C. It includes a Control and Timing Unit and a data handling unit that accepts the analog signal from the RFES logarithmic detector. It digitizes it and performs the required sample averaging of 0.16 s.
To detect the low reflectivity of clouds, the CPR averages many samples of the measured power and subtracts the estimated system noise level. The number of independent samples can be increased by increasing the PRF (Pulse Repetition Frequency). However, the maximum PRF is given by the range ambiguity considerations. For CPR, the nominal range window size is set to 30 km, permitting the capture of the surface return and cloud return up to an altitude of 25 km. The system noise level is estimated using the clear air radar return from 25 to 30 km altitude. The radar footprint is 1.4 km, and is averaged over 0.16 seconds to produce an effective footprint of 3.5 km (along-track) by 1.2 km (cross-track). 32) 33)
Table 1: CPR instrument parameters
Figure 7: Simplified block diagram of CPR
Figure 8: The HVPS (High-Voltage Power Supply) device of CPR (image credit: NASA/JPL)
Figure 9: Illustration of the CPR antenna subsystem (image credit: NASA/JPL)
Figure 10: Illustration of the CloudSat spacecraft (image credit: NASA/JPL)
Legend of Figure 10: This artist's concept shows NASA's CloudSat spacecraft and its Cloud Profiling Radar using microwave energy to observe cloud particles and determine the mass of water and ice within clouds.
The CPR instrument is the first-ever millimeterwave and the most sensitive radar so far launched into space. Its -30 dBZ detection sensitivity is enabling the first global view of the vertical structure of the atmospheric clouds at 500 m resolution. The CloudSat mission also provides an important demonstration of the 94 GHz radar technology in a spaceborne application.
The validation of the data products uses remote sensing measurements from surface and airborne platforms together with in-situ aircraft measurements of relevant cloud parameters as well as matching aircraft data with satellite data after launch. The validation strategy also involves the exploitation of existing cloud data bases. The CloudSat validation plan benefits from the systematic measurement programs of ARM as well as selected sites within Europe, regular aircraft radar measurement activities within the USA, Japan and Europe, measurement capabilities at a number of universities, and field-experiment activities representing targets of opportunity are planned in the coming years.
1) G. L. Stephens, D. G. Vane, “The CloudSat Mission,” IGARSS 2003, Toulouse, France, July 21-25, 2003
2) E. Im, S. L. Durden, C. Wu, “Development Status of the Cloud Profiling Radar for the CloudSat Mission,” IGARSS 2003, Toulouse, France, July 21-25, 2003
3) F. K. Li, E. Im, S. L. Durden, R. Girard, G. Sadowy, C. Wu, “Cloud Profiling Radar (CPR) for the CloudSat Mission,” Proceedings of IEEE/IGARSS 2000, Honolulu, HI, July 24-28, 2000
5) G. L. Stephens, D. G. Vane, S. J. Walter, “The CloudSat Mission: A new Dimension to space-based Observations of Cloud in the coming Millennium,” paper presented at the GCSS-WGNE Workshop, Fort Collins, CO, Nov. 9-13, 1998
6) G. L. Stephens, “CloudSat and the EOS Constellation,” Proceedings of IGARSS/IEEE, July 9-13, 2001, Sydney, Australia
7) G. L. Stephens, “On the Combination of Active and Passive measurements - In the study of Clouds and Precipitation,” Proceedings of IGARSS/IEEE, July 9-13, 2001, Sydney, Australia
8) “Shadowing Satellite Science - The CloudSat Ground Validation Program,” CSA, Nov. 28, 2007, URL: http://www.asc-csa.gc.ca/eng/satellites/cloudsat.asp
9) G. L. Stephens, D. G. Vane, R. J. Boain, G. G. Mace, K. Sassen, Z. Wang, A. J. Illingworth, E. J. O'Connor, W. B. Rossow, S. L. Durden, S. D. Miller, R. T. Austin, A. Benedetti, C. Mitrescu, and The CloudSat Science Team, “The CloudSat Mission and the A-Train,” BAMS (Bulletin of the American Meteorological Society), Vol. 83, Issue 12, Dec. 2002, pp. 1771-1790, URL: http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-83-12-1771
10) “CloudSat, NASA Facts,” URL: http://www.nasa.gov/pdf/136796main_cloudsat-factsheet.pdf
11) NASA CloudSat-CALIPSO Press Kit, April 2006, URL: http://www.nasa.gov/pdf/147741main_cloudsat-calipso4.pdf
13) G. L. Stephens, D. G. Vane, R. J. Boain, G. G. Mace, K. Sassen, Z. Wang, et al., “The CloudSat Mission and the A-Train,” BAMS, Dec. 2002, pp. 1771-1790
14) Donald E. Keenan, “Cloudsat Formation Flying with CALIPSO,” Proceedings of the 32nd AAS Guidance and Control Conference, Breckenridge, CO, USA, Jan. 31.- Feb. 4, 2009, AAS 09-043
15) “CloudSat radar status,” Colorado State University, Dec. 11, 2013, URL: http://cloudsat.atmos.colostate.edu/news/CloudSat_status
16) Elizabeth Ritchie (Chair), Ana Barros, Robin Bell, Alexander Braun, Richard Houghton, B. Carol Johnson, Guosheng Liu, Johnny Luo, Jeff Morrill, Derek Posselt, Scott Powell, William Randel, Ted Strub, Douglas Vandemark, “NASA Earth Science Senior Review 2013,” June 14, 2013, URL: http://science.nasa.gov/media/medialibrary/2013/07/16/2013-NASA-ESSR-FINAL.pdf
17) Ian J. Gravseth, Brian Pieper, “CloudSat’s Return to the A-Train,” Proceedings of the 5th International Conference on Spacecraft Formation Flying Missions and Technologies (SFFMT), Munich, Germany, May 29-31, 2013, “ URL of paper: http://www.sffmt2013.org/PPAbstract/4071p.pdf, URL of presentation: http://www.sffmt2013.org/PPAbstract/4071pr.pdf
18) “CloudSat radar status,” Colorado State University, 'Update of Feb. 13, 2013, URL: http://cloudsat.atmos.colostate.edu/news/CloudSat_status
19) “CloudSat returns to the A-Train,” May 15, 2012, URL: http://www.cloudsat.cira.colostate.edu/dpcNewsItem.php?newsid=68
20) “Data Processing Center News,“ CIRA, URL: http://www.cloudsat.cira.colostate.edu/dpcstatusTrack.php
21) Michael Nayak, Mona Witkowski, Deborah Vane, Thomas Livermore, Mark Rokey, Marda Barthuli, Ian J. Gravseth, Brian Pieper, Aaron Rodzinak, Steve Silva, Paul Woznick, “CloudSat Anomaly Recovery and Operational Lessons Learned,” Proceedings of SpaceOps 2012, The 12th International Conference on Space Operations, Stockholm, Sweden, June 11-15, 2012
22) 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
23) “CloudSat radar status,” Colorado State University, Update of Sept. 21, 2011, URL: http://cloudsat.atmos.colostate.edu/news/CloudSat_status
24) 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
25) Debra Werner, “NASA Budget fpr Earth Science Lags Behind Rising Expectations,” Space News, January 4, 2010, p. 1 & 4
26) S. Tanelli, S.L. Durden, G. Dobrowalski, “CloudSat’s Cloud Profiling Radar (CPR): status, performance and new products,” CloudSat/CALIPSO STM, Madison, WI, July 28, 2009, URL: http://cimss.ssec.wisc.edu/.../Tanelli_CloudSat_Cloud_Profiling_Radar.pdf
27) D. Vane, G. L. Stephens, “The CloudSat Mission and the A-Train: A Revolutionary Approach to Observing Earth's Atmosphere,” Proceedings of the 2008 IEEE Aerospace Conference, Big Sky, MT, USA, March 1-8, 2008
28) G. Stephens, J. Kay, J. Haynes, “NASA Satellites Help Lift Cloud of Uncertainty on Climate Change,” AGU Conference, San Francisco, CA, Dec. 2007, URL: http://cloudsat.atmos.colostate.edu/agu_cloudsat_press.ppt
29) Eastwood Im, Chialin Wu, Stephen L. Durden, “Cloud Profiling Radar for the CloudSat Mission,” IEEE Aerospace and Electronic Systems Magazine, Vol. 20, Issue 10, Oct. 2005, pp. 15-18, URL: http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/37690/1/042971.pdf
31) R. LaBelle, R. Girard, G. Arbery, “A 94 GHz RF Electronics Subsystem for the CloudSat Cloud Profiling Radar,” 33rd European Microwave Conference (EUMC), 2003, IEEE Vol. 3, Oct. 7-9, 2003, Munich, Germany, pp. 1139-1142, URL: http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/40462/1/03-1835.pdf
32) Eastwood Im, Simone Tanelli, Stephen L. Durden, Kyung Pak, “Cloud Profiling Radar Performance,” Proceedings of IGARSS 2007 (International Geoscience and Remote Sensing Symposium), Barcelona, Spain, July 23-27, 2007
33) E. Im S. L. Durden, S. Tanelli, K. Pak, “Early Results on Cloud Profiling Radar Post-launch Calibration and Operations,” Proceedings of IGARSS 2006 and 27th Canadian Symposium on Remote Sensing, Denver CO, USA, July 31-Aug. 4, 2006
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.