CALIPSO
Science Validation Plan
PC-SCI-501
Dave Winker and Chip Trepte
Jacques
Pelon and Anne Garnier
Institut
Pierre Simon LaPlace, Paris, France
Tom Kovacs
Version 4.0
December 2004
TABLE OF CONTENTS
1 INTRODUCTION............................................................................................................................................................................................. 3
1.1 Purpose.................................................................................................................................................................................................. 3
1.2 Scope....................................................................................................................................................................................................... 3
1.3 Applicable Documents................................................................................................................................................................ 3
1.4 Revision History............................................................................................................................................................................... 4
1.5 Acronyms and Abbreviations
Glossary......................................................................................................................... 5
2 BACKGROUND.............................................................................................................................................................................................. 7
2.1 Mission Overview............................................................................................................................................................................ 7
2.2 Science Objectives........................................................................................................................................................................... 7
2.3 Instruments and Measurements......................................................................................................................................... 8
2.4 Aqua Constellation and Orbit
Information.............................................................................................................. 9
2.5 Science Data Products............................................................................................................................................................... 9
2.6 Success Criteria............................................................................................................................................................................ 10
3 VALIDATION APPROACH...................................................................................................................................................................... 11
3.1.1 Calibration and
Characterization............................................................................................................................. 11
3.3.1 Field Campaigns......................................................................................................................................................................... 11
3.1.2 Algorithm
Evaluation................................................................................................................................................................ 12
3.1.3
Correlative Measurement Planning........................................................................................................................................ 12
3.1.4
Correlative Instrument Development and Characterization.............................................................................................. 12
3.2 On-orbit Validation................................................................................................................................................................... 13
3.2.1 Level 1 Data Products................................................................................................................................................................ 14
3.2.2 Level 2
Aerosol Products........................................................................................................................................................... 16
3.2.3 Level 2 Cloud
Products............................................................................................................................................................. 19
3.3 Correlative Data Sources..................................................................................................................................................... 22
3.3.1 Field Campaigns......................................................................................................................................................................... 23
3.3.2 Ground-based
Measurements................................................................................................................................................... 26
3.3.3 Satellite
Comparisons................................................................................................................................................................ 29
3.3.4 Data
Assimilation and Models................................................................................................................................................. 30
3.4 Data Access Policy...................................................................................................................................................................... 30
3.5 Data Ingest and Display Tools........................................................................................................................................... 31
4. IMPLEMENTATION SCHEDULE............................................................................................................................................................ 32
4.1 Data Release Requirements.................................................................................................................................................. 32
4.2 Satellite Assessment Phase
(L+0 to L+40 days)........................................................................................................... 32
4.3 Initial Instrument Validation
(L+40 days to L+135 days).................................................................................... 33
4.4 Primary Validation Phase
(L+135 to L+18 months).................................................................................................... 34
4.5 Continued Data Assessment Phase
(post L+18 months)........................................................................................ 35
4.6 CALIPSO Validation Milestones
(referenced to Launch Readiness Date)................................................. 35
5. MANAGEMENT........................................................................................................................................................................................... 35
6. Contact Information..................................................................................................................................................................... 36
The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Validation Plan provides an overview of the requirements and approach for validating Level 1 and Level 2 science data products from the CALIPSO satellite mission.
This validation plan addresses pre-launch and post-launch activities for validating the Level 1 and Level 2 Science Data Products of the CALIPSO satellite mission. The document provides an overview of the mission objectives and payload instrumentation in section 2. General information and procedures for calibration and validation of the data products are described in section 3. These are followed with specific implementation plans for the three validation phases of the mission in section 4 and identification of primary oversight responsibilities in section 5. As they are part of the CALIPSO Science Data Products, but are defined as level 4 products, only a brief discussion is provided in this document for the validation of surface and atmospheric fluxes products retrieved using combined CERES and CALIPSO observations. These plans are further detailed in the CERES SARB Validation Plan. Plans are not included in this document for validating other products derived from synergistic algorithm retrievals with measurements from other satellite platforms in the A-Train constellation. Details on pre-launch and in-flight instrument calibration activities are described in the CALIPSO Algorithm Theoretical Basis Documents C-SCI-201 and C-SCI-203. Routine quality assurance and algorithm improvement activities are not covered in this plan.
PC-SYS-101 Science and
PC-SCI-201 Algorithm Theoretical Basis Document Lidar Level 1
PC-SCI-202 Algorithm Theoretical Basis Document Lidar Level 2
PC-SCI-203 Algorithm Theoretical Basis Document IIR Level 1
PC-SCI-204 Algorithm Theoretical Basis Document IIR Level 2
PC-SCI-205 Algorithm Theoretical Basis Document WFC Level 1
PC-SCI-503 CALIPSO Data Products Catalogue
PC-SCI-504 Quid Pro Quo Validation Plan
This plan will be updated periodically, or as warranted by instrument or algorithm developments or by changes in comparison strategies.
Version 0.7 December 2002 Preliminary draft
Version 0.8 February 2003 Preliminary draft
Version 1.0 April 2003 Baseline plan
Version 2.0 January 2004 Updated information
Version 3.0 July 2004 Updated information
Version 4.0 December 2004 Updated information
AATS
AD-NET Asian Dust Network
AERONET The Aerosol Robotic Network
AIRS Atmospheric Infrared Sounder
AMMA African Monsoon Multidisciplinary Analyses
ARM Atmospheric Radiation Measurement
ATBD Algorithm Theoretical Basis Document
ASDC Atmospheric
AVE Aura Validation
Experiment
BSRN Baseline Surface Radiation Network
CALIOP Cloud and Aerosol Lidar with Orthogonal Polarization
CALIPSO Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations
CERES Clouds and the Earth’s Radiative Energy System
CMDL Climate Monitoring and Diagnostic Laboratory
CNES Centre National
d’Etudes Spatiales
CNRS Centre National de la Recherche Scientifique
DEM Digital Elevation Maps
DIRAC IIR instrument simulator
ICESAT Ice, Cloud and Land Elevation Satellite
IIR Imaging Infrared Radiometer
INTEX Intercontinental
Chemical Transport Experiment
IPSL Institut Pierre
Simon Laplace
IRR Infrared Imaging Radiometer
IWC Ice Water Content
LAABS Langley A-Band Spectrometer
LEANDRE Multi-Wavelength airborne Backscatter Lidar (IPSL)
LITE Lidar In-Space Technology Experiment
LNG LEANDRE New Generation
LOA Laboratoire d’Optique Atmosphérique
MAS MODIS Airborne Simulator
MISR Multi-Angle Imaging Spectro-Radiometer
MODIS Moderate Resolution Imaging Spectroradiometer
MSG Meteosat Second Generation
NASTI NPOESS Airborne Sounding Testbed Interferometer
NASA National Aviation and Space Administration
NDSC Network for the Detection of Stratospheric Change
OMI Ozone Measuring Instrument
PARASOL Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar
PDF Probability Distribution Functions
POAM Polar Ozone and Aerosol Measurement
POLDER POLarization and Directionality of Earth Reflectances
QPQ Quid Pro Quo
REALM Regional East Atmospheric Lidar Mesonet (REALM).
SAGE Stratospheric Aerosol and Gas Experiment
SARB Surface And Atmospheric Radiation Budget
SEVIRI Spinning Enhanced Visible and Infrared Imager
SMRD Science and
SNR Signal-to-Noise Ratio
SURFRAD Surface Radiation Budget Network
TBD To be determined
WCRP World Climate Research Program
WFC Wide Field Camera
WRS World Reference System
Cloud-Aerosol Lidar and Infrared
Pathfinder Satellite Observations (CALIPSO) is a satellite mission designed to
measure the vertical structure and optical properties of aerosol and clouds
over the globe that are needed to better understand their role in the climate
system. This knowledge will lead to
improvements in our ability to model and predict climate variability and
long-term climate change. The mission is co-sponsored by the
The CALIPSO
payload consists of three instruments: a two-wavelength polarization-sensitive
lidar referred in the remainder of this document as the Cloud and Aerosol Lidar
with Orthogonal Polarization (CALIOP); a three-wavelength Imaging Infrared
Radiometer (IIR); and a single-channel visible imager or Wide Field Camera
(WFC). This suite of instruments will be placed in a sun-synchronous orbit and
will fly in formation with the Aqua satellite constellation (e.g., Aqua,
CloudSat, CALIPSO, PARASOL, and Aura satellite missions) to obtain
near-coincident measurements with active and passive instruments on these other
platforms. The CALIPSO mission is scheduled for launch (with CloudSat) during
the summer of 2005 and has a planned operational lifetime of 3 years.
Aerosols directly affect the Earth’s energy balance by scattering and absorbing shortwave solar radiation, and by absorbing and emitting longwave infrared radiation. They can also indirectly affect this balance by influencing the properties and process of clouds though their role as cloud condensation nuclei. Aerosols further play a significant role in the chemical evolution of trace gases and pose serious air quality and health concerns when concentrations are large. The physical and optical properties of aerosols are complex and vary considerably due to differences in composition, sources, and environmental conditions.
Model estimates of global aerosol radiative forcing are highly uncertain, largely because observations are insufficient to constrain or verify key assumptions in these models. Synergistic measurements from the A-train will enable the first observationally based estimate of direct aerosol forcing. The CALIPSO mission will provide profiles of aerosol backscatter and extinction coefficients over the globe. Its multi-spectral and polarization measurements will further provide height-resolved information on aerosol type. These measurements will be combined with near simultaneous measurements from A-train instruments of aerosol optical parameters (i.e., MODIS, OMI, and PARASOL), atmospheric state (e.g., AIRS, MLS), and radiative fluxes (CERES) to provide estimates of direct aerosol forcing and key independent variables that control it.
Understanding the effects of clouds on Earth’s radiation balance, and particularly on longwave fluxes within the atmosphere and at the surface, depends on having accurate knowledge on the location of clouds vertically within the atmosphere and their multi-layer structure as well as having knowledge of their phase and ice/water content. Coincident profile information from CALIPSO’s lidar and from CloudSat’s radar offers a unique opportunity to map the vertical structure of clouds over the globe with accuracy never before realized. The combination of these data with observations from other A-train instruments (e.g., MODIS, CERES, and PARASOL) will provide more accurate measurements of surface longwave fluxes and atmospheric heating rate profiles that are needed to improve weather forecasting and climate prediction.
The CALIPSO mission will also provide new observations on cloud physical and optical properties that are needed to better understand cloud feedback processes. Presently, the largest uncertainties in predicting climate are associated with modeling a variety of cloud-radiation-climate feedback processes. Because of the short time scales and nonlinear relationships typical of cloud processes, the only way to verify the representation of these processes in models is with nearly simultaneous observations of atmospheric state, cloud physical and optical properties, and of the radiation field. Observations from CALIPSO and the other satellites of the A-train will provide an unprecedented suite of measurements to investigate these complex processes.
The CALIPSO instrument payload
is designed to operate autonomously and continuously. The CALIOP laser
transmitter subsystem consists of two redundant lasers, each with a beam
expander, and a beam steering system. The Nd:YAG lasers are diode-pumped and
operate at 1064 nm and 532 nm with a pulse
repetition rate of 20.25 Hz. Beam
expanders are used to reduce the angular divergence of the laser beam to a
diameter of 70 meters at the Earth’s surface.
The lidar receiver subsystem is designed to measure 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).
This subsystem consists of the telescope, relay optics, detectors,
preamps, and line drivers mounted on a stable optical bench. A fixed field stop
located at the telescope focus defines the 130 µrad field of view. 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 needed to measure both cloud and molecular
backscatter signals. An active boresight system is used to ensure co-alignment
between the transmitter and the receiver.
The fundamental sampling resolution of CALIOP is 30 meters vertical and 333 meters horizontal, which is determined by the receiver electrical bandwidth and the laser pulse repetition rate. Backscatter data will be acquired from the surface to 40 km. Because of limitations to the downlink telemetry bandwidth, lidar profiles will be averaged on-board both vertically and horizontally to reduce the data volume. This averaging will begin in the upper troposphere and extend upwards into the stratosphere. In this region, lidar profiles will be reduced to a vertical resolution of 60 m and a horizontal resolution of 1 km. In the stratosphere, the profiles will be further degraded to a vertical resolution of 180 m and a horizontal resolution of 5 km.
CALIOP profiles will be
calibrated by normalizing the return signal to the predicted backscatter
coefficients derived from meteorological observations in the aerosol-free
region between 30 km and 35 km. On-board calibration hardware will be used to
calibrate the 532 nm perpendicular channel relative to the 532 nm parallel
channel. The 1064 nm channel will be calibrated
relative to the 532 nm total backscatter signal using optically thick cirrus
clouds as reference targets.
The IIR and WFC instruments are both nadir viewing and co-aligned with the lidar. The IIR provides calibrated radiances at 8.65 mm, 10.60 mm, and 12.05 mm over a 64 km swath, with a spatial resolution of 1 km. Spectral bandwidths are respectively 0.9 mm, 0.6 mm and 1 mm. These spectral characteristics were chosen to optimize joint lidar/IIR retrievals of cirrus emissivity and particle size. The IIR detector consists of a microbolometer array in a non-scanning, staring configuration, which allows for a simple and compact design. For on-orbit calibration, the IIR will use a dual approach that views either a temperature-monitored black body source or deep space. Independent comparisons will also be made with calibrated measurements from ground-based and airborne sensors.
The WFC consists of a single channel covering the 620 nm to 670 nm spectral region and provides images with a 61 km swath and a pixel resolution of 125 m. The WFC provides meteorological context for the lidar measurements and allows highly accurate spatial registration, when required, between CALIPSO and instruments on other satellites of the Aqua constellation. WFC data will be acquired only during daylight conditions and will be used for the retrieval cloud properties.
CALIPSO will be flown 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 98o. Aqua will lead the constellation with an equatorial crossing time of about 1:30 PM. CloudSat and CALIPSO will lag Aqua by 1 to 2 minutes and will be separated from each other by 10 to 15 seconds. PARASOL is planned to fly ~2 minutes behind CALIPSO. Aura will be last in the formation separated from Aqua by about 15 minutes.
For the first 2 years of the mission, the nadir track of CALIPSO and CloudSat will be offset eastward from the Aqua nadir track by approximately 215 km at the equator. This shift permits comparisons with MODIS aerosol products in regions that would have been otherwise masked by sun glint during the northern hemispheric summer. During the third year of the mission, the current plan is to allow CALIPSO to precess westward across the swath of MODIS and CERES to view aerosol and cloud properties at a variety of viewing angles.
The satellites in the A-train
will be 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 will
complete 14.55 orbits per day with a separation of 24.7o longitude
between each successive orbit at the equator. The orbit tracks at the equator
will progress westward 10.8 o on succeeding days, which over a
16-day period, will produce 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 at: http://landsat.gsfc.nasa.gov/documentation/wrs.html
The CALIPSO Level 2 Science Products are defined in the Algorithm Theoretical Basis Documents (ATBD) and are listed in detail in the Data Products Catalogue (PC SCI 503). These products will be produced and archived at the Langley Atmospheric Sciences Data Center (ASDC). Table 1 gives a summary of the CALIPSO Level 2 data products and the spatial scales at which the data products will be reported. The expected accuracies given are for the maximum averaging distances for which the products will be retrieved. Cloud products will be reported at a horizontal resolution of 5 km; i.e., at the fundamental averaging resolution of the processing scheme. Cloud boundaries, which can be detected at higher resolution, will be reported at that resolution. To account for weaker backscatter signals from aerosols, the Level 2 aerosol profile products will be reported at a uniform horizontal resolution of 40 km at all altitudes.
Table 1. CALIPSO Level 2 Aerosol and Cloud Measurements
|
Data Product |
Measurement
Capabilities and Uncertainties |
Data Product
Resolution |
|
|
Horizontal |
Vertical |
||
|
Aerosols |
|||
|
Height, thickness |
For layers with b >
2.5 x 10-4 km-1
sr-1 |
5km |
60 m |
|
Optical depth, t |
40% * |
5 km |
N/A |
|
Backscatter, b a(z) |
20 - 30% |
40 km 40 km |
Z < 20 km 120 m Z ³ 20 km: 360 m |
|
Extinction, sa(z) |
40 % * |
40 km 40 km |
z < 20 km 120 m z ³ 20 km: 360 m |
|
Clouds |
|||
|
Height |
For layers with b >
1 x 10-3 km-1
sr-1 |
1/3, 1, 5 km |
30, 60 m |
|
Thickness |
for
layers with t < 5 |
1/3, 1, 5 km |
30, 60 m |
|
Optical depth, t |
within
a factor of 2 for t < 5 |
5 km |
N/A |
|
Backscatter, b c(z) |
20 - 30% |
5 km |
60 m |
|
Extinction, sc(z) |
within
a factor of 2 for t < 5 |
5 km |
60 m |
|
Ice/water
phase |
Layer
by layer |
5 km |
60 m |
|
Ice
cloud emissivity, e |
±0.03 |
1 km |
N/A |
|
Ice
particle size |
±50% for e > 0.2 |
1 km |
N/A |
|
Note: * assumes 30% uncertainty
in the aerosol extinction-to-backscatter lidar ratio, Sa |
|||
The CALIPSO science data products are considered to be validated if either the uncertainty estimates for the geophysical products have been shown to hold, based on comparisons with independent data products of high quality that have already been validated themselves, or the discrepancies between such comparisons have been understood and explained. A goal of the validation effort is to provide the user community with sufficient information to explain the quality of the data, in terms of precision and relative accuracy, and the spatial/temporal variations in these quality attributes.
For the CALIPSO mission, validation is defined as an assessment of the accuracy and precision of the derived science products by independent means. This includes an end-to-end understanding and characterization of the instrument, algorithms, and databases that will be used to generate data products and estimates of their uncertainties. It also includes activities that verify whether the data products are of sufficient quality to address its primary science objectives. Validation of Level 1 data products focuses on the calibration and verification of instrument performance (e.g., SNR, linearity) and the algorithms used for geolocation and lidar altitude registration. Validation of Level 2 data products is concerned with the quantification of the random and bias errors in the data products, as well as verifying the underlying assumptions on which the retrieval algorithms are based.
Validation of Level 2 products requires comparisons with independent measurements. Independent measurements of CALIPSO Level 2 parameters are required as well as of parameters on which the CALIPSO retrievals depend, such as aerosol or cloud lidar ratio. “Independent” is understood to mean that the measurements used for validation are direct or at least do not rely on the same assumptions as the CALIPSO retrieval algorithms.
Because the CALIPSO instruments have very narrow measurement swaths, spatial coincidence between measurements from validation instruments and CALIPSO is not guaranteed and consideration must be given to spatial matching of the measurements relative to the spatial variability of the aerosols and clouds sampled. Inter-comparisons with measurements from other satellites, particularly other satellites in the A-train, are attractive in that a large, global set of coincident data can be obtained. However, care must be taken to understand the measurement uncertainties and limitations of the retrieval techniques used to derive the parameters being inter-compared with CALIPSO data products. It should be noted that for some Level 2 products, such as ice water content, comparison data sets are difficult to obtain. For these products, validation will be based mostly upon consistency checks.
This chapter provides an overview of the validation approach adopted for the CALIPSO mission with a general discussion on the strategy and concerns. Details on the validation schedule and specific measurement activities are provided in Section 4.
The accuracy and precision of retrieved science measurements depends critically on knowledge of the payload instruments response to incident radiation. It is the objective of pre-launch instrument characterization and calibration activities to quantify the response of CALIOP, the WFC, and the IIR over a range of operating conditions to very precise levels. These activities will include measurements of the linearity and transient recovery of the detector system. Atmospheric tests were conducted for the lidar system before payload integration (completed December 2003) to verify the boresight mechanism and obtain some information on instrument performance. Another set of measurements are planned at the launch site (scheduled for April 2005). For the IIR, pre-launch activities included characterization of the absolute radiometric response of the IIR referenced to a standard laboratory source. Measurements also included an assessment of the spectral transfer function of each IIR channel and characterization of the linearity of the detectors.. Calibration procedures are detailed in a CNES Ground Calibration Specifications Document. The IIR calibration performance budget is described in a document that will be issued by CNES after checkout activities. No pre-launch atmospheric testing activities for the IIR or WFC are planned.
Pre-launch validation activities will include the use of simulated CALIOP, IIR, and WFC observations to test algorithms and data handling software. Simulated data sets derived from observational data sets such as the Lidar In-Space Technology Experiment (LITE) and the ER-2 aircraft Cloud Profile Lidar (CPL) and MODIS Airborne Simulator (MAS) instruments that were deployed during SAFARI 2000 and CRYSTAL-FACE are used to represent the characteristics of the CALIPSO instrument suite and the expected observed atmospheric variability. Algorithm retrieval studies will be conducted using these data sets to test performance. Simulated data sets will be also generated using prescribed aerosol and cloud characteristics as inputs to CALIOP and IIR instrument forward models. In this manner, Level 1 and 2 retrieval algorithms will be tested for a variety of realistic atmospheric conditions and instrument settings.
The science data processing software undergoes multiple tests as part of the development process as well as formal acceptance tests after the implementation of all major software revisions. Information on the software development activities, verification studies, and quality assurance plans are found in the Quality Assessment plans in the Data Management Plan (PC-SCI-502).
Plans for acquiring correlative measurements have been developed during the pre-launch phase and include the identification and establishment of agreements with cooperative ground-base measurement facilities under the Quid Pro Quo (QPQ) Validation Plan, development of a QPQ validation website (http://calipsovalidation.hamptonu.edu), and the development of plans for dedicated aircraft flights and integration of measurement requirements in international field campaigns. Additional studies include the preparation of statistical analysis and data assimilation techniques.
To a large degree, the CALIPSO validation program will be built upon comparisons from well characterized and understood instruments with long measurement records. Validation of some of the CALIPSO products, however, requires additional correlative information that exceeds the capabilities or availability of these resources. To satisfy these needs, several instrument systems are either under development or modification that are aimed at supporting CALIPSO validation. For CALIPSO lidar products, two new airborne High Spectral Resolution Lidar (HSRL) systems are being developed: one by NASA LaRC and another by IPSL. These instruments will complement airborne elastic lidar systems operating at similar wavelengths, which by themselves can satisfy a number of correlative measurement requirements for CALIOP. However, for the validation of backscatter and extinction profile measurements, additional information is needed. This is necessary because the retrieval of these products from backscatter lidar measurements requires a priori knowledge of a backscatter-to-extinction coefficient, also known as the lidar ratio. The lidar ratio, which is noted for aerosols as Sa and clouds as Sc, depends on particle size, composition, and shape and can vary by a factor of ~5 or more. The distribution of Sa is poorly known and is a major source of uncertainty in the retrieval of extinction, perhaps as large as 30%. Knowledge of Sc is also important for clouds of intermediate optical thickness.
Several ground-based Raman and HSRL lidars have been operational for a number of years and provide unambiguous measurements of the altitude resolved backscatter coefficient, extinction, and the lidar ratio. To improve matching criteria between satellite and correlative sensors, similar airborne lidars are desired for CALIPSO validation. Unfortunately, construction of an airborne Raman lidar system operating at a wavelength of 532 nm is not practical because of the poor sensitivity of its cross section. Improved signal-to-noise can be achieved with higher transmission power, but only at levels that are not eye-safe for ground and airborne observers. The alternative HSRL systems operating at the same wavelength, on the other hand, are ~1000 times more sensitive and are eye-safe.
For these reasons, compact HSRL
systems are currently under development by NASA LaRC and IPSL. These systems
will be deployed on aircraft to provide correlative measurements along the
CALIPSO ground track. IPSL’s LEANDRE New Generation (LNG) lidar provides
depolarization and high spectral resolution measurements at 355 nm. The
instrument also operates as a conventional elastic lidar at 532 nm and 1064 nm.
NASA’s HSRL provides depolarization and high spectral resolution measurements
at 532 nm. It also provides elastic
backscatter and depolarization measurements at 1064 nm. Measurements from these
instruments should greatly aid in the determination of uncertainties with
CALIPSO’s aerosol and cloud retrievals. Developing an inventory of Sa
by location, altitude, and season will also be valuable for other elastic lidar
systems such as GLAS.
To support validation of the CALIPSO IIR, two airborne infrared sensors are planned to be operated by French scientists. IPSL’s DIRAC instrument is a CALIPSO IIR simulator with 4 spectral channels that uses rotating filters (3 channels matched to the CALIPSO IIR and a fourth channel matched to the 11 mm channel on MODIS) and uses the same micro-bolometer detector array design as the CALIPSO IIR. CLIMAT (developed by LOA and CIMEL) is a narrow FOV IR radiometer that also acquires measurements at the same 3 spectral channels as CALIPSO. These instruments can be further complemented by a 5-channel mid-IR radiometer with measurement of the polarized reflectance at 1.6 mm and 2.2 mm to retrieve the effective size of ice crystals. All of these instruments have undergone preliminary testing and are expected to be flown in concert with IPSL’s HSRL (LEANDRE New Generation (LNG)) during validation flights. A visible camera will also be included to simulate the full CALIPSO instrument payload.
In addition to these airborne instruments, IPSL is developing a couple of mobile remote sensing facilities for clouds and aerosols. One of these systems, Transportable Remote Sensing Station (TreSS), has been developed at LMD and will include a 2 wavelength, depolarization mini-lidar, an IR radiometer with spectral bands covering 9.5 – 11.5 mm, a pyranometer, and a 4-channel sunphotometer. The intent is to deploy the facilities under CALIPSO ground-tracks, thereby, improving comparison opportunities with well-matched observations.
Comparisons with correlative measurements obtained from well-characterized instruments will serve as the primary basis for evaluating the relative accuracy of the derived data products. Self-consistency analysis, limit checks, and sensitivity analysis will also be used to evaluate instrument performance and data uncertainties.
The difference between two measurements that are not exactly collated in space or time or have different resolutions will include some measure of geophysical variability, which is unrelated to measurement uncertainty. Where matching errors are small relative to the spatial correlation scales, validation can be done by direct inter-comparison of measurements. In other cases, averaging and other statistical techniques can be used to reduce uncertainties due to matching errors to reveal the errors due to measurement and retrieval. Comparisons with observations from long-term ground stations can also be performed, where regional statistics from CALIPSO are compared with local statistics compiled over a long time period.
The deployment of correlative instruments on aircraft platforms during field campaigns allows co-location with CALIPSO measurement locations. Field campaigns can also contribute to validation through the use of instrument simulators. CALIPSO retrievals will be tested on data acquired both before and after launch by airborne simulators. With proper experiment design, these retrievals can be validated using other data acquired during the field campaign. This approach minimizes many of the sampling issues involved in inter-comparing validation data with CALIPSO observations themselves.
Specific validation approaches are identified for the various products listed below. Included in the discussion are suggested guidelines on matching criteria and techniques for correlative measurements.
The primary validation tasks for Level 1 data products include verification of geolocation, assessment of pointing biases, and evaluation of on-orbit calibration. This activity will include an assessment of the instrument signal-to-noise ratio (SNR), linearity, as well as radiometric calibration.
Lidar footprint geolocation and altitude registration: Altitude registration can be verified through comparisons between the measured altitude of the ocean surface with estimates computed using satellite ephemeris and attitude data. The geolocation of the lidar footprint can be verified through comparisons with surface Digital Elevation Maps (DEM). The CALIPSO geolocation requirement is for the lidar footprint to be co-located within a 1 km resolution pixel observed by MODIS on Aqua. The GTOPO30 DEM from the U.S. Geological Survey is a possible reference source with a spatial resolution of approximately 30 arcsec (~1 km at equator) and vertical resolution of 30 m. Digital maps from the Space Shuttle Radar Topography Experiment provide an alternative data source with superior spatial resolution (horizontal resolution 30 m and vertical resolution of 5-10 m); however, this coverage currently extends only over the continental United States. Location errors and pointing biases will be determined from differences between the lidar surface return height and the DEM data at the footprint locations.
Imager pixel geolocation: The geolocation of the IIR and WFC image pixels and their position relative to the lidar footprint will be evaluated both along and perpendicular to the spacecraft ground track through comparisons with identifiable, high contrast landmarks such as coastlines using high-resolution DEMs. This procedure has been widely used by other satellite experiments and is reviewed in the WFC ATBD.
Lidar profile calibration: The 532 nm parallel channel will be calibrated in-flight by normalizing the backscatter coefficients above 30 km where molecular scattering dominates. Baseline subtraction, correction of baseline shape effects, and the on-orbit merging algorithm will be verified by looking at heavily averaged clear-air profiles (i.e., no aerosols). The 1064 nm channel will be calibrated through cross comparisons with the 532 nm backscatter observations from optically thick cirrus clouds. The 532 nm perpendicular channel will be calibrated relative to the parallel channel using a pseudo-depolarizer, which can be inserted into the received beam on command. Measurements of clouds having high and low depolarization with ground-based or airborne depolarization lidars can be used to check the calibration of the depolarization gain ratio and to assess uncertainties in the depolarization of the transmitted beam. Details of the lidar calibrations are contained in the lidar Level 1 ATBD.
IIR radiance calibration: The IIR will be calibrated in orbit employing sequential views of a temperature-monitored warm black body radiance source (~295 K) and deep space at ~4 K. These observations will allow determination of the detection gain and offset for each spectral channel and each pixel. Details of the IIR on-orbit calibration algorithm are described in the CNES IIR/Calipso Level 1 processing requirements. Calibrated radiances will be verified through consistency checks and direct and indirect comparisons. Both the radiometry and the spectral response of the three IIR channels have to be checked over a brightness temperature range of 220 to 310 K. As the solar reflectance should not impact radiances in the thermal IR region, both daytime and nighttime comparisons will be useful to identify biases. Initial calibration analysis will rely on vicarious comparisons of clear sky measurements over oceans.
In the level 2 IIR processing algorithm, the IIR radiances (brightness temperatures) utilize comparisons with radiative transfer model computations under clear sky and dense cloud conditions. It relies on the use of operational atmospheric profiles (temperature and humidity) and surface conditions (temperature and emissivity). CALIOP observations are used to identify clear sky pixels along the satellite track. For data processing activities, temperature and humidity profiles will be obtained from operational GMAO meteorological products. For special comparison studies, coincident radiosonde profile measurements will be required. Measurements over the ocean will require concurrent sea surface temperature from buoys or from satellite measurements such as AIRS/AMSU/HSB, MODIS, CERES or SEVIRI.
Comparisons of measured and calculated brightness
temperatures over land are also -envisaged for homogeneous areas where the
surface emissivity and temperature can be measured locally or from satellite
measurements such as ASTER. Calibration studies over
Direct comparisons with
measurements from other instruments over a variety of atmospheric conditions
will be conducted. Measurements will be
made above cloud scenes to ensure similar viewing to the IIR. Plans are to acquire correlative measurements
on-board the Falcon 20 aircraft with the DIRAC/CALIPSO instrument simulator and
the CIMEL IR radiometer CLIMAT . This aircraft has a nominal flight service ceiling
of 39,000 feet and should be sufficient to fly above mid altitude clouds in all
seasons and cirrus in winter. Comparisons are being considered with MAS on the
ER-2. Indirect comparisons with high spectral resolution IR spectrometers will
permit an assessment of the unfiltered IIR spectra. Comparisons can be obtained
with AIRS observations in the 8.8-15.4 mm
region or with airborne measurements from the NPOESS Airborne Sounding Testbed
Interferometer (NASTI). Ground-based up-looking AERI radiometers at the ARM
sites may also be used under clear sky conditions, preferably in association
with a backscatter lidar. In addition, standard resolution radiometers may
provide valuable comparison observations. Examples include the DIRAC IIR
simulator (when not involved in a field campaign) or the CIMEL IR radiometer
CLIMAT, currently operated at the IPSL instrumental site near Paris (
Direct comparisons are planned on
a regular basis with simultaneously observing IR spectro-radiometers having
similar channels: MODIS, AIRS, and CERES on AQUA and the SEVIRI imaging
radiometer on the Meteosat Second Generation (MSG) spacecraft are being
considered.. MSG was launched in August
2002 into a geostationary orbit stationed over Europe and
WFC radiance calibration: Calibration of the WFC will be based primarily upon vicarious comparisons with nighttime views of the Earth and daytime views of tropical deep convective clouds as standard dark and bright targets, respectively. Additional comparisons will be made with near-simultaneous MODIS observations. Details of the WFC on-orbit radiance calibration are covered in the WFC Level 1 ATBD.
Aerosols have complex physical and optical properties that can vary with changes in environmental conditions. Observations suggest that coherent space and time scales for aerosol concentration are on the order of 100 km or less and range from minutes to hours, respectively. These scales place limits on matching requirements between correlative measurement activities and CALIPSO observations. Greatest coincidence will be obtained with measurements from aircraft platforms deployed along the CALIPSO satellite orbit track and within a few minutes of its overpass. Coincidence opportunities for direct comparisons between CALIPSO observations and ground-based instruments, on the other hand, are not as straight forward. A preliminary guideline for obtaining matched aerosol coincidences is for the CALIPSO ground track to pass within 100 km of an instrument site and within an hour of the satellite overpass. This guideline attempts to balance differing horizontal resolution scales for the CALIPSO data products against the limited matching opportunities available from other instruments with narrow field-of-views, while still ensuring that common aerosol structures are viewed by both measurement systems. For correlative measurements that do not fall within these match criteria, comparisons will be conducted based on ensemble averages and probability distributions.
Height and thickness: Validation of the altitude registration is addressed in Level 1 activities. The primary concern for the validation of aerosol layer height and thickness, however, is in determining the detection limits of the CALIPSO aerosol/cloud detection algorithm. For this requirement, comparisons of aerosol layer height and thickness with correlative backscatter lidar profile measurements are needed for a variety of aerosol loadings (as well as a variety of cloud types and cloudiness). Ground-based and airborne backscatter lidar systems can provide the necessary correlative data.
Backscatter profile, extinction profile and optical depth: The accuracy of retrieved profiles of aerosol backscatter, extinction and the column optical depth is dependent upon measurement uncertainties as well as the underlying assumptions of the retrieval algorithm. For backscatter lidars such as CALIOP, the retrieval of these parameters relies heavily upon an estimation of Sa. For elevated layers, the retrieval scheme determines optical thickness from the difference between the molecular backscatter above and below the layer. A layer-averaged Sa can be estimated from the measurement itself and the optical thickness is then used to constrain the retrieval of backscatter and extinction. For aerosol layers that are not elevated, the retrieval algorithm estimates Sa on the basis of aerosol type using a variety of information including the ratio between 532 and 1064-nm backscatter and the depolarization at 532 nm.
For validation of aerosol backscatter and extinction profiles at 532 nm, lidar observations offer the best opportunity for evaluating the accuracy of these products in the troposphere. Correlative measurements from established backscatter lidar sites such as those participating the European EARLINET program and the MPL network will be particularly valuable for placing CALIPSO measurements within the context of long and broad measurement records. Airborne backscatter lidar measurements (e.g., CPL) are also valuable for evaluating aerosol backscatter and extinction. As noted before, however, the retrieval of these products is highly dependent upon estimates of Sa, which can have uncertainties of perhaps 30%. One approach for obtaining a more self-consistent extinction measurement is to co-locate a multi-wavelength sun photometer and backscatter lidar so that estimates of Sa are constrained by column optical depth observations. This approach would be acceptable for layers that are homogenous, but would be less appropriate over an altitude range where Sa varies significantly. For these conditions, HSRL and Raman lidars are believed to be more advantageous because they provide unambiguous profile measurements of backscatter, extinction, and Sa over the entire column with vertical resolution of a few hundred meters. Differential height measurements of optical depth using airborne radiometers also provide a means for obtaining profiles of aerosol extinction. These measurements have been made with considerable success in previous field experiments. However, they can extend only a limited horizontal range because of the time required for the aircraft to conduct spiral ascent or descent maneuvers.
For the validation of column aerosol optical depth, comparisons will be conducted with correlative measurements from surface and airborne multi-wavelength sun photometers and radiometers (e.g., AERONET and AATS-14). Comparisons with satellite retrievals of optical depth may also provide added insight. For example, in periods with aged, well-mixed volcanic aerosol conditions in the stratosphere, Sa is reasonably well known. Comparisons can be accomplished with satellite measurements from SAGE III, POAM III or MAESTRO, which provide extinction and optical depth products at similar wavelengths to CALIOP. Additional direct and indirect comparisons between CALIPSO data sets and other ground-based instrument facilities and satellite measurements such as MODIS, MISR, OMI and GLAS will provide an understanding of relative biases and variations between data sets.
In addition to obtaining a limited set of coincident correlative measurements for CALIPSO to test aerosol retrievals, comprehensive measurements of Sa are needed to refine the algorithm that is used to select estimates of Sa. Measurements are needed that address the generalized aerosol types listed in Table 2. This objective would not necessarily require coincident measurements with CALIPSO and could be obtained from existing ground-based instrument facilities (as indicated in Table 2) or during airborne field missions.
Table 2. Regions with Characteristic Aerosol Types of Particular Interest
with a few Representative Measurement Sites
|
Aerosol Type |
Height/Thickness |
ta |
sa |
Sa |
|
Urban/polluted India/Indian Ocean |
Washington DC Buenos-Aires 22 EARLINET sites, Anhui Institute, CJFEPC Pune |
8 Aeronet sites 12 MFRSR sites 13 Aeronet sites 4 BSRN sites Hamburg, Jungfraujoch, Kuehlungsborn, Leipzig, Palaiseau 6 Aeronet sites Yulin, MALE, |
Kuehlungsborn, Leipzig |
Kuehlungsborn, Leipzig |
|
Biomass burning |
Brasil Reunion Island Darwin |
Alta Floresta, Cuiaba, Abracos Hill, Santa Cruz Etosha Pan, Mongu, Skukusa Darwin |
Reunion Island* Darwin* |
Reunion Island* Darwin |
|
Desert dust Saharan, southern Asian and east |
6 AD-NET sites, |
5 Aeronet sites |
|
|
|
Polluted marine (sea
salt, sulfate, soot) |
Aberystwyth, |
|
Aberystwyth*, |
|
|
Dusty marine (sea salt,
sulfate, dust) |
Kyung Hee, Nagasaki |
Capo Verde, Bermuda |
Kyung Hee* |
Kyung Hee* |
|
Clean Continental America,
Europe |
SGP, Haute Provence, Minsk |
Bratts Lake (Regina), Rimrock, Alice Springs, Pellston, Minsk SGP (23 sites) |
SGP* |
SGP* |
|
Clean Marine (sea salt) |
Manus, Nauru, Mauna Loa, Dumont d’Urville, Ny Alesund |
Manus, Nauru, Hilo, Mauna Loa, Tahiti, Kwajalein, Ny Alesund |
Manus*, Nauru* |
Manus*, Nauru*, Mauna Loa* |
|
Arctic haze |
Barrow, Ny Alesund |
Barrow, |
Barrow |
Barrow |
An estimate of the multiple scattering parameter, h, is also needed for retrievals of aerosol (and cloud) extinction and optical depth. This parameter accounts for the apparent reduction in optical depth produced by multiple scattering and can be range-dependent. One approach is to measure the aerosol phase function using a polar nephelometer and compute h using a multiple scattering code. Although it is uncertain if polar nephelometers have sufficient sensitivity to provide the needed measurements. The most promising technique for estimating h within aerosol layers is to compare lidar profiles from CALIPSO with a down-looking narrow-FOV aircraft lidar. The ratio of the normalized, range-corrected returns from these lidars can be taken as equivalent to the ratio of total scatter to single scatter and used to compute h directly. An airborne multiple field-of-view lidar (e.g., CPL), which mimics the viewing geometry of CALIOP and also has a narrow field-of-view, would allow direct measurement of h appropriate for CALIPSO.
Table 3 summarizes the above discussion by listing the principal Level 2 aerosol data products and instruments that might be used to acquire inter-comparison data for validation, including tests of some of the underlying retrieval assumptions. A variety of other internal data products, not listed here, will be produced and used during data processing activities. Validation of these other products will rely on using CALIPSO products that have established levels of uncertainty or by inference. For example, backscatter color ratio profiles (ratio of backscatter profiles at 2 wavelengths) provide information on aerosol size distribution. A validation approach would be to compare these values with measurements on particle size from in situ particle samplers or derived from multi-wavelength observations from a sun photometer.
Table 3. Correlative Measurement Requirements for Aerosol Products
|
Principal Parameters to be
Validated |
Candidate Comparison
Instruments |
|
layer
height, thickness |
G/B: backscatter lidar A/C: backscatter, HSRL lidar |
|
backscatter,
b a(z) extinction, sa(z) lidar ratio, Sa (z) |
A/C:
HSRL, Raman lidar, 180-nephalometer G/B:
HSRL, Raman lidar, elevation-scanned backscatter lidar |
|
optical
depth, t |
G/B:
up-looking sun photometer,
radiometer, airborne: HSRL or Raman lidar satellite:
e.g., MODIS, MISR, PARASOL, SAGE III, OMI |
|
Sa (layer averaged) |
G/B:
backscatter lidar & sun photometer A/C:
backscatter lidar & radiometer satellite:
CALIPSO & PARASOL |
|
multiple
scattering parameter, h(z) |
CALIPSO
and airborne nadir viewing lidar |
G/B = ground-based, A/C = aircraft
In contrast to tropospheric aerosols, clouds have relatively short lifetimes (often on the order of minutes to hours) and even shorter correlation spatial scales (a few kilometers to tens of kilometers). These constraints greatly complicate the validation of retrieved cloud properties by direct comparison with instruments at ground-sites. Because of the difficulty in obtaining large datasets of coincident aircraft measurements of different cloud types, it is also unlikely that a data set will become available from airborne measurement to comprehensively test Level 2 products. For these reasons, a more profitable validation approach is to acquire airborne measurements of a few critical parameters that may be directly compared with CALIPSO observations and rely on comparisons of measurement ensembles from different techniques, locations, and periods for other parameters. A similar approach is the basis of the CERES validation effort and is also being considered for CloudSat validation.
Comparisons with CALIPSO cloud retrievals under a variety of conditions are needed: water clouds, ice clouds, mixed phase clouds; optically thin and thick clouds; clouds with large and small particles; cirrus formed by various generating mechanisms at different latitudes (frontal, synoptic, anvil, etc). Whether clouds are broken or overcast and single- or multi-layer is not so important from a retrieval point of view, but imposes different constraints on matching errors and suitability of comparison data. It is also necessary to test cloud retrievals in a variety of climate regimes with varying cloud properties. Since the deployment of field campaigns to all the regions of interest is not practical, efforts will be focused on a few major climate regimes. For example, convective clouds and cirrus dominate a significant portion of the tropics, low altitude stratus or scattered cumulus exist over large portions of the marine subtropics, highly variable storm systems occur often in the mid latitudes, and a wide variety of ice and water clouds occur in the polar regions.
Cloud height and thickness: Altitude registration issues are addressed by Level 1 activities. The detection of clouds by lidar observations is largely a sensitivity issue, which is less critical for clouds than for aerosols because of the higher signal levels. Direct comparisons with an airborne lidar and a high-resolution radiometer (e.g., DIRAC/LEANDRE and MAS/CPL) offers one of the best approaches for identifying cloud and aerosol features needed for verifying the CALIPSO cloud/aerosol detection algorithm. Preference is given to downward looking lidars because of cloud attenuation and to match the CALIPSO viewing volume. Insight on CALIOP detection thresholds for cloud bases may also be obtained through satellite data comparisons with MODIS cloud products. Coincident radar profile measurements from CloudSat will also be valuable for inter-comparing the height boundaries of clouds over the globe.
Cloud extinction profile and optical depth: Validation of cloud optical depth will primarily focus on comparisons using two different approaches. The first approach relies on measurements of solar radiance through clouds by upward-looking ground-based or airborne radiometers, while the second approach employs measurements of cloud transmission from ground-based and airborne lidars. Measurements from in situ particle samplers can provide estimates of both optical depth and extinction profiles. However, in situ observations have sparse coverage because they require the aircraft to fly profile patterns and have added uncertainties associated with small sampling volume and calculations of extinction. Coincident A-train measurements will also provide powerful comparison opportunities. MODIS optical depth measurements will be extremely useful for single-layer cloud situations (as identified by CALIOP) and optimum sun angles. Additional cloud information will be available from CloudSat and PARASOL.
Profile measurements of Sc
and h are also needed. For cirrus,
estimates of Sc can be derived from direct cloud transmission
measurements obtained from airborne lidar observations. Because of the small
field of view of airborne lidar, this technique would have the added advantage of
having reduced multiple scattering effects, allowing for an assessment of the
magnitude of h for clouds. A
layer-average Sc can be estimated from measurements from a sun
photometer optical depth and backscatter lidar; however, sun photometer optical
depth must be corrected for small-angle cirrus forward scatter. As with aerosols, h could be assessed from direct comparison with aircraft lidar
returns. Estimates of h are also
available by indirectly measuring the cirrus phase function with in situ
instruments including a polar nephelometer such as the one at LAMP in
Cloud ice/water phase and ice water content: It is expected that ground-based depolarization lidar observations will be useful for validation of CALIPSO depolarization profiles in the absence of low altitude clouds. Airborne depolarization lidar are preferred to reduce matching errors and increase observational capability. For aircraft observations, down-looking lidar measurements are needed to validate CALIPSO cloud phase measurements for low altitude and optically thick clouds where the compensation for multiple scattering effects in the retrieval needs to be checked. Direct in situ measurements of ice and water contents (e.g., Nevzorov sonde) can be useful in aiding the interpretation of depolarization lidar measurements. Comparisons with MODIS and PARASOL ice/water phase products should prove to be useful in cases of single-layer or opaque cloud.
Cirrus emissivity and particle size: Effective emissivity, ec, of a semi-transparent upper cloud is calculated from the relationship, ec = (Li - Lo)/( (Lb - Lo), where Li is the upward radiance measured by the IIR, Lo is the outgoing sky radiance in the absence of the studied cloud layer, and Lb is the radiance from an opaque cloud at the radiatively equivalent temperature of the semi-transparent cloud. For CALIPSO, ec and particle size data products for cirrus and other high altitude clouds will be derived from combined IIR radiances and lidar observations such as cloud height and depolarization characteristics for cloud systems having 1-3 layers. Extension across the swath will be derived from statistics on the homogeneity of the cloud field under the track combining IIR, lidar and WFC data for daytime periods. The algorithm uses ancillary data such as temperature and humidity profiles and surface emissivity and temperature. Validation of CALIPSO emissivity products will include comparisons from down-looking airborne instruments such as the combined DIRAC IIR simulator, LNG and visible camera instrument suite and dropsondes (when possible). It is also planned to make comparisons using an up-looking ground-based and radiosonde instrumentation on dedicated sites with characterized surface emissivity. Satellite comparisons of derived cloud products from MODIS or SEVIRI may also prove to be beneficial for single-layer cirrus scenes. It is planned also to check the emissivity retrieved over clouds identified as opaque by the lidar.
Comparison of cirrus particle size will be based largely on statistical comparisons with ground-based instruments such as multiple field of view lidars and either backscatter or Raman lidars combined with cloud profiling radars. As the robustness of the particle size retrieval depends upon both their size and shapes in relation with the wavelength range (between 8 and 12 mm), multi-instrumented sites with measurement in the visible, in the thermal IR and at larger microwave wavelengths can provide particle size measurements in complementary ranges. Airborne down-looking observations above the clouds using a multi-instruments payload such as the CALIPSO payload simulator, a cloud radar (operating at the same wavelength than Cloudsat), a mid-IR polarized radiometer and an airborne version of the radiometer/polarimeter POLDER would be therefore of great interest. Particle size and shape can be more directly measured with some accuracy using airborne in situ instruments, such as a Cloud Particle Imager, but there are several types of sampling difficulties, including the measurement sensitivity as a function of size and the very different sampling volumes between the in situ and satellite instruments. CALIPSO cirrus particle size can also be checked for consistency with satellite measurements in the A-train (for example comparing to retrievals from MODIS visible and near IR channels) or from SEVIRI. For the most part, particle size information will be retrieved only when the cloud emissivity ranges from ~0.1 to 0.9 (optically thin clouds) and the cloud layers are unambiguously identified.
Table 4 summarizes the above discussion by listing the principal Level 2 cloud data products and instruments that might be used to acquire inter-comparison data for validation, including tests of some of the underlying retrieval assumptions. The table also includes estimates on spatial matching requirements. As with aerosols, a variety of other data products not listed here will be produced. Validation of these other products will generally be accomplished either by inter-comparing CALIPSO parameters with quantities derived from the basic validation measurements or by inference, when the quantities are derived from validated CALIPSO products. In addition, there are a few derived products (cloud type, ice water content), which will need to be addressed specifically.
Table 4. Validation Measurement Requirements for Clouds
|
Principal Parameters to be
Validated |
Horizontal Resolution
Requirements |
Candidate Comparison
Instrument |
|
cloud layer heights |
20-50 km |
backscatter lidar |
|
optical depth, t |
1-5 km |
G/B*: radiometers/sun photometers A/C*: backscatter lidar, HSRL Satellite: MODIS, PARASOL (single-layer clouds) |
|
Sc,eff (layer-average) |
~ 50 km |
Backscatter lidar |
|
spectral emissivity, e(li) (layer- average) |
1-5 km |
A/C: radiometers and backscatter lidar (DIRAC/LEANDRE; MAS/CPL) Satellite: MODIS, AIRS, MSG/SEVIRI (single layer cirrus) |
|
effective particle size, Deff |
1-5 km |
G/B and A/C: radiometers,
backscatter lidar with cloud-profiling radar, A/C: in situ measurements, Satellite : MODIS/AQUA, SEVIRI/MSG (few cases) |
|
extinction profile, sc(z) |
1-5 km |
Raman lidar, HSRL, in situ samplers |
|
lidar ratio profile, Sc (z) |
1-5 km |
Raman lidar, HSRL, in situ samplers |
|
d(z) |
1-5 km |
Depolarization lidar |
|
ice/water phase |
1-5 km |
Depolarization lidar, G/B radiometer, MODIS, ASTER, PARASOL, in situ samplers |
|
emissivity assumptions |
1-5 km |
P,T,U sounding, ASTER |
|
multiple scattering parameter, h(z) |
|
CALIPSO and airborne backscatter lidar airborne multiple-field of view lidar (CPL, LNG) |
* G/B = ground-based, A/C = aircraft
It is important to emphasize that, in addition to a variety of measurements intended to perform independent measurement of Level 2 parameters, it is also important to acquire airborne simulator data, which can be used as inputs to the retrieval codes.
This section provides an overview of the sources of correlative measurements utilizing instrument techniques identified above that may be available for CALIPSO validation. The primary source of data needed to test retrieval algorithms will be from of airborne measurement activities such as during the TC4 Costa Rica or TWP-ICE field experiments. Over the lifetime of the CALIPSO mission, valuable correlative measurements will also be obtained from established ground-based instrument facilities around the globe that will be used to assess the relative accuracy of the retrieved data products. Comparisons with these observations will also permit an understanding of the context of CALIPSO’s measurements within the long-term aerosol and cloud observational records collected at many ground-based sites. Through these activities, satellite and ground-based remote sensing and in situ measurements can be integrated (employing suitable resources) to provide a more comprehensive data set needed to unravel the subtle relationships that control aerosol forcing.
Data from different measurement programs will be made available to the CALIPSO science team either through established validation or campaign archival sites (e.g., CRYSTAL-FACE, Aura Validation) or through the CALIPSO QPQ data depository.
Field campaigns are intensive observational activities that focus on specific objectives for brief periods and limited areas. Typically, the missions are designed to acquire a comprehensive set of observations that can explore atmospheric processes and support satellite validation activities in greater detail than available with conventional measurement programs. Over the next 5 years, NASA, CNES, and other international organizations are planning a variety of field missions that complement CALIPSO science interests and validation needs. It is through these measurement activities that many comparison activities will be realized. Members of the CALIPSO project and science team are engaged with program leaders of these different missions to help coordinate synergistic and correlative measurement opportunities. Below is a listing of possible field missions, with information on their primary focus of interest. Information is also provided for each mission on types of measurements that would benefit either CALIPSO validation or related science studies.
Dedicated CALIPSO Aircraft Measurements: In the early phase of the mission, aircraft flights are required to obtain essential comparison data to help quickly assess the performance of the instruments and provide initial information on the accuracy of the retrieval algorithms. Plans are to initially deploy both NASA’s and IPSL’s HSRL lidar systems on high altitude aircraft and fly along the satellite ground-track to examine Level 1 and a few Level 2 products. These will be complemented by elastic lidar cloud measurements from CPL over the tropics and mid latitudes. Coincident measurements from surface based and the NASA/AATS-14 and LOA/PLASMA airborne multi-channel sun photometers are also planned to obtain a complementary assessment on column optical depth or layer extinction. (see section 4.3 for more details).
Several other instruments will
also be flown several months after launch to further analyze aerosol and cloud
properties. IPSL’s DIRAC instrument and the CLIMAT IR radiometer have the same
spectral channels as the IIR and will provide an opportunity for direct
comparisons of spectral radiances as well as derived products. The mid-IR polarized radiometer, the
radiometer/polarimeter POLDER and various in situ measurements will provide a
characterization of the cirrus ice crystals. RALI combines a Doppler radar with
LNG to provide an instrument payload similar to that employed by CALIPSO and CloudSat. RALI is
also planned to be flown in
Intercontinental Chemical
Transport Experiment (INTEX) North America: The INTEX-NA field mission is
designed to examine the composition and chemical evolution of tropospheric
aerosols and trace gases that are exported to and from
AURA Validation Experiment (AVE): AVE seeks to better understand the structure of the troposphere and the coupling between the troposphere and stratosphere. The mission is considering a combination of in situ and remote sensing instruments on a high altitude aircraft to:
- Characterize the influx of material from the stratosphere into the troposphere,
- Investigate relationship between ozone precursors and ozone production in the tropics and polluted regions,
-
Assess pollutant inflow and outflow over
-
Improve our understanding of convective
detrainment of pollutants.
Aircraft flights will be
coordinated to support Aura validation activities; and hence will complement
other A-train elements such as CALIPSO validation and science studies. AVE began in 2004 and is planned to conduct
measurements through 2006.
Tropical Composition, Cloud
and Climate Coupling (TC4) or Tropical Clouds Systems and Processes
(TCSP): TC4 seeks to
quantify the transport, radiative, and chemical processes, and the coupling
between these processes in the lower tropical stratosphere and the upper
tropical troposphere (referred as the Tropical Tropopause Layer - TTL). A
mission concept is being developed that will interweave Aura validation
activities with specific process studies using a variety of high altitude
aircraft/balloon platforms and ground-based instruments. Different science goals include a better
understanding of processes that control water vapor in the TTL and the
formation and distribution of thin cirrus and their influence on radiative
heating/cooling. The mission is also interested in obtaining an understanding
the fates of short-lived compounds from the tropical boundary layer into the
TTL as well as acquiring an understanding the mechanisms that control ozone in
the tropical troposphere. The TC4 is being considered for mid summer
2005 with a base of operations in
The Tropical Warm
Pool-International Cloud Experiment (TWP-ICE): TWP-ICE will attempt to
describe the evolution of tropical convection including the large-scale heat,
moisture, and momentum budgets along with detailed observations of cloud
properties and the impacts of the clouds on the environment. An explicit objective of the experiment is to
provide validation data for the A-train.
The experiment is a collaboration between the DOE ARM project, the
Australian Bureau of Meteorology, NASA, the European Commission, and a number
of universities. The mission will be
conducted from
TWP-ICE plans to perform
extensive characterization of tropical cirrus using both in situ and remote
sensing aircraft. The experiment will
use a number of aircraft of various capabilities to conduct flight missions at
low levels (< 5000 ft), mid-levels (15-30,000 ft) and high altitudes
(50-60,000 ft). Continuous measurements
will be provided by the Darwin ARM site and a ship located about 200 km west of
Saharan Mineral dust experiment (SAMUM): SAMUM is designed to better understand the radiative effects of Saharan dust. The field campaign consists of aircraft, balloon, and ground-based instruments with numerical modeling activities. The project plans to begin operations in 2005. (http:// /www.tropos.de/samum).
Megacity Impacts on
Regional and Global Environments (MIRAGE):
The goal of MIRAGE is to better characterize the chemical and physical
transformations and fate of pollutants exported from large urban areas and to
assess the impact of these pollutants on regional and global air quality,
ecosystems and climate.. The mission is primary sponsored by NSF and will be
formed around the deployment NCAR’s C-130 aircaft in the region surrounding
Cirrus Cloud Experiment
(CIRCLE2): The CIRCLE experiment led by DLR seeks added information on the
formation of mid-latitude cirrus and how aerosols can affect cirrus
microphysical properties. The field campaign is planned in the autumn of 2006
in southern
African Monsoon Multidisciplinary Analyses (AMMA): An international field mission is planned to improve our understanding of the West African monsoon. Specific areas of interest include how each of the following influence or are influenced by the monsoon circulation atmospheric dynamics, continental water cycle, atmospheric chemistry, continental and oceanic surface conditions. This mission involves field experiments coupled with satellite observations and modeling at different temporal and spatial scales. Four special observing periods are planned: the first is scheduled for January-February 2006 during the dry phase, when dust and biomass burning aerosols co-exist and the others during the wet phase (late spring and summer 2006). Observations include balloon atmospheric soundings, airborne measurements with the new French ATR and Falcon 20, ground-based and oceanic measurements. CALIPSO validation flights are under consideration during the dry and the wet season. (http://www.joss.ucar.edu/amma/)
Arctic Study of
Tropospheric Aerosol, clouds, and Radiation (ASTAR) and Antarctic trace Gas and
Aerosol airborne Measurement Study (AGAMES).
ASTAR and AGAMES field missions are being led by the Alfred Wegener
Institute for Polar and Marine Research (
Canadian Validation Support for CloudSat/CALIPSO. The Canadian Space Agency will sponsor intensive aircraft comparison activities tailored to the validation of mid and high latitude cloud systems primarily during the cold weather season. Activities are scheduled for January-April 2006 The effort will include airborne flights with the NRC Convair 580 with in situ and remote sensing instruments (lidar/radar). Additional airborne flights with a Cessna 207 aircraft are also possible for summer months (lidar). These activities will be coordinated with other ground-based and mobile research facilities to optimize correlative measurements opportunities and scientific analysis.
Stratosphere-Climate Links
with emphasis on the UTLS (SCOUT-O3). The European Union is sponsoring a major
research initiative with studies covering ozone depletion and climate change,
upper troposphere and lower stratosphere composition and transport processes,
satellite validation, modeling activities. One aspect of the program is
obtaining measurements in the UT/LS in tropical regions. Plans are now being
considered for aircraft observations in the
An important activity for CALIPSO validation is to link its measurements with those from established ground-based instruments over the globe. These are being organized under the CALIPSO Quid Pro Quo (QPQ) Validation Program. Comparisons between these data sets will permit an understanding of relative biases and place satellite measurements within the context of published observational records. Integrating measurements between different platforms also permits the formation of synergistic data sets that can explore complex multi-faceted physical processes. For example, the fusion of observations will particularly be valuable for better understanding the magnitude of the anthropogenic signal of aerosol forcing, for only with the combination of satellite, in situ, and modeling resources does sufficient information exist on the extensive and intensive properties of aerosols and the partitioning between natural and anthropogenic sources to address this issue.
A large number of ground-based instrument facilities make routine observations and can provide valuable correlative measurements for CALIPSO validation and collaborative science investigations. In general, the location of these facilities is somewhat scattered over the globe, but biased towards northern mid latitudes. Because CALIPSO will be in a high inclined orbit and tied to the WRS grid, the frequency of near coincident measurement opportunities with CALIPSO will be better at high latitude sites where orbits converge near the pole and poorer at low latitudes where the separation between orbits is greatest. Since clouds have high spatial and temporal variability relative to aerosols, correlative measurements for clouds (especially near active convection or near the boundary layer) require a greater degree of coincidence than for aerosols. A statistical approach can be used where validated long-term surface measurements (such as at ARM sites) are compared statistically with regional satellite measurements.
A brief summary of
ground-based networks that may support CALIPSO validation is provided below.
Some of these sites such as those at Ny-Ålesund,
Palaiseau, and the ARM sites and have been identified as being key validation
locations. Dr. Tom Kovacs at
The Aerosol Robotic Network (Aeronet): The Aeronet is a federated network, with over 60 sites distributed over the globe, of sun photometers for the derivation of aerosol parameters (aerosol optical depth, inferred size distribution, refractive index, and phase function). (http://aeronet.gsfc.nasa.gov:8080/)
Asian Dust Network (AD-NET): The AD-Net is an international virtual community begun in February 2001 for the rapid notification and exchange of data of Asian dust events. (http://info.nies.go.jp:8094/kosapub/index.html).
Atmospheric Radiation Measurement (ARM)
Program: Three highly instrumented facilities (Climate and Radiation Test
Beds or CART) sites have been developed by the Department of Energy for
measuring radiative energy flux profiles for clear and cloudy conditions. Sites
are located at Southern Great Plains site in
Baseline Surface Radiation Network (BSRN): BSRN is a project of the World Climate
Research Program (WCRP) aimed at detecting important changes in the earth's
radiation field, which may cause climate changes. The BSRN provides
observations of the short and longwave surface radiation flux. These readings
are taken from a small number of selected stations, in contrasting climatic
zones, together with collocated surface and upper air meteorological data and
other supporting observations. (http://bsrn.ethz.ch/).
Canadian Research Facilities: The
Canadian Space Agency will sponsor an extensive correlative measurement program
for the CloudSat satellite experiment beginning in the summer of 2005. at several sites to determine the
dependencies of cloud characteristics by season. Ground-based lidar and radar
measurements will be available from the CARE and King Radar facilities near
Climate Monitoring and Diagnostics
Laboratory (CMDL): The CMDL of the
National Oceanic and Atmospheric Administration (NOAA) conducts research
related to the atmospheric constituents that are capable of forcing change in
the climate of the earth or may deplete the ozone layer. Aerosol measurements
began at the CMDL baseline observatories in the mid-1970s as part of the
Geophysical Monitoring for Climate Change. The goal of this regional-scale
monitoring program is to characterize means, variability, and trends of
climate-forcing properties of different types of aerosols, and to understand
the factors that control these properties. (http://www.cmdl.noaa.gov/aerosol/)
European Aerosol Research Lidar Network
(EARLINET): EARLINET is a network of 22 ground-based
lidar stations. Many of these facilities have additional remote sensing sensors
that provide added information on aerosol properties. The program was funded until 2003 by European
Union and now operates on a voluntary basis (http://lidarb.dkrz.de/earlinet/index.html).
Micropulse
Lidar Network (MPLNET): MPLNET is a worldwide network of micro-pulse,
autonomous single-channel (532 nm) lidar systems. The network is designed to
provide long-term data sets of cloud and aerosol vertical distributions at key
sites around the globe, and also serve as ground-truth sites for satellite
measurement programs. MLPNET sites are co-located with AERONET sun photometers.
(http://mplnet.gsfc.nasa.gov/). The combined
instrument facility located at the Chesapeake Lighthouse is of considerable
interest because of its use in previous satellite validation campaigns and
possible reference site for aircraft activities during early stages of the
validation effort.
Network for
the Detection of Stratospheric Change (NDSC): This network includes ~60 ground-based stations
worldwide and a few mobile instruments, aimed at high-quality remote sensing of
stratospheric composition and its changes over time. (http://www.ndsc.ws).
Observatoire
de Physique de l’Atmosphere de La Reunion (OPAR): The OPAR station is located on
The Regional
East Atmospheric Lidar Mesonet (REALM): REALM is a confederation of operational and planned
lidar sites in eastern
Site Instrumental de Recherche par
Télédétection Atmosphérique (SIRTA): SIRTA
is a comprehensive aerosol and cloud measurement facility supported IPSL that
includes a backscatter multi-channel, depolation aerosol/cloud lidar, a water
vapor Raman lidar, a 94 GHz radar, solar photometers, and radiometers located
at Palaiseau, France. Observations from this site will provide important
correlative measurements for validation and collaborative science studies. Past
and future measurements provide valuable support for the development of
synergistic retrievals of cloud and aerosol properties from A-train
instruments. (http://sirta.lmd.polytechnique.fr/index_english.htm).
Surface Radiation Budget Network (SURFRAD): SURFRAD was established in 1993 through the
support of NOAA's Office of Global Programs. The SURFRAD mission's primary
objective is to support climate research with accurate, continuous, long-term
measurements of the surface radiation budget over the
Mobile Remote
Sensing Stations: Both Canadian
and French research organizations are supporting the deployment of mobile
remote sensing laboratories to provide direct comparisons of aerosol and cloud
layer structures for CALIPSO. The TreSS (Transportable Remote Sensing Station)
and LESAA mobile stations are sponsored by CNES and CNRS and will provide
profile information on backscatter and extinction coefficients as well as
information on the effects of multiple scattering. The TreSS facility will
consist of a multi-channel mini-lidar, an IR radiometer (9.5-11.5 um), a
pyranometer, and a 4-channel sun photometer. It is envisioned that the mobile
laboratories would collect measurements primarily in -
Comparisons with other satellite measurements will permit an assessment of relative biases of different data products between sensors for a variety of aerosol and/or cloud scenes over the globe. These studies may also provide insight into the spatial and temporal coherence of features detected by CALIPSO. Table 5 provides a partial listing of satellite observations that are expected to be available during the CALIPSO mission. Care must be exercised to ensure that products have similar sampling volumes and scenes are clearly understood before they are used for comparisons.
Table 5. Satellite Comparison DataSets
|
Instrument |
Spacecraft |
Measurement |
|
AIRS |
Aqua |
Reconstruction
of IIR filtered radiances |
|
ASTER |
Aqua |
High
spatial resolution surface emissivity |
|
CERES |
Aqua/Terra |
Long-term
stability (window 8-12 mm) |
|
CloudSat |
CloudSat |
t, cloud heights |
|
GLAS |
ICESAT |
t, sa(z), aerosol/cloud heights |
|
MISR |
Terra |
t, index of refraction |
|
MODIS |
Aqua/
Terra |
t, cloud fraction, cirrus
particle size, emissivity, radiance |
|
OMI |
Aura |
ta(z), aerosol index |
|
PARASOL |
PARASOL |
t, aerosol index, cloud particle phase |
|
SAGE
III |
Meteor
3M |
Stratospheric
t, sa(z) |
|
SEVIRI |
MSG |
Radiance
measurements, evaluate temporal sampling errors |
Combination of data from active and passive sensors on A-train satellites with operational ground-based instruments offers an unprecedented opportunity to better understand the effects of aerosols and clouds on climate and weather. Fusing these multiple data sources, however, is not straightforward because of inherent differences in measurement techniques and retrieval assumptions. Advanced data assimilation techniques and three-dimensional model simulations offer considerable promise for blending these resources and exploiting their full potential. It is hoped that through these tools insight into subtle correlations of between atmospheric parameters will be illuminated and better understood. The CALIPSO mission will seek to engage different assimilation and modeling groups for their support in CALIPSO validation and science studies.
Access to data acquired during CALIPSO validation activities will be in accordance with NASA’s data and information policy.
The CALIPSO project is producing data ingest software for all of its Level 1 and 2 products that will be made available at the ATSC and the CALIPSO website (http:/www-calipso.larc.nasa.gov/. The software code will be prepared in IDL and MATLAB.
To support data comparisons, satellite predict information will also be made available at the CALIPSO website. This information will be updated on a bi-weekly basis.
The validation schedule outlined below is designed to support the verification and release of data products in three phases. The first phase is designed to support a preliminary or Beta release approximately 135 days after launch. This data set will include Level 1 products and a subset of Level 2 science data products as listed in Table 6. The second phase will support the release of validated Level 1 and 2 data products approximately 18 months after launch (see Table 1 or the Data Catalogue (PC-SCI-503) for an expanded description). The third phase will continue instrument and data product assessment studies to support a final report at the end of the mission Appropriate documentation describing the current assessment of the data products will accompany each data release. Publications on data quality will also be submitted to refereed journals. A comprehensive validation report of the entire data set will be prepared after the completion of the planned 3-year mission.
Table 6.
Preliminary (Beta) CALIPSO science data release.
|
Data Level |
Data Products |
Production Schedule |
|
1 |
· Calibrated lidar profiles · Calibrated IIR radiances · Calibrated WFC radiances · Meteorological profiles · Lidar aerosol & cloud
browse images |
Preliminary (Beta) release
following on-orbit checkout (L+135 days).
Data produced on 2-day lag thereafter. |
|
2 |
· Aerosol layer
height/thickness · Cloud height/thickness |
Preliminary (Beta) release following on-orbit
checkout (L+135 days). Data produced on 3-day lag thereafter. |
The initial 40-day period following launch is designated as the Satellite Assessment Phase. During this period the satellite will be maneuvered into formation with Aqua; platform and payload systems will be activated and characterized. Under the nominal Assessment Phase schedule, instruments will be activated ~7 days after launch and begin checkout activities. An In-flight Acceptance Review will signal the transition to routine satellite operations.
Routine science operations are scheduled to begin approximately 40 days after launch. During the first few months of the mission, the Project team will focus mainly on internal assessments of the instrument performance and calibration activities. For the lidar, initial analysis will include evaluation of laser energy, pointing and timing accuracy, stability of system constants, estimation of signal-to-noise ratios (day/night), and clear air depolarization. For the IIR and WFC, initial analysis will focus on pixel geolocation accuracy, image quality assessment, dark current and gain assessment, and internal calibration activities. Examination of Quality Assurance (QA) reports generated as part of the routine data stream will be especially useful for identifying trends and deviations from expected behavior of Level 1 and 2 data handling routines and retrieval algorithms (see the CALIOP QA, WFC QA, and the IIR Level -1 documentation for details).
During this early phase, several
mission specific correlative measurement efforts are being organized and
sponsored by NASA and CNES to aid assessment activities with external
comparisons. Within the first week of operation, a
couple of flights with the NASA’s HSRL on board a chartered LearJet are planned
along the spacecraft’s ground-track. These measurements should provide early
feedback on altitude registration and overall instrument performance. More
comprehensive analysis will be gained from a series of planned activities
targeted at differing aerosol and cloud scenes during July – September. To support aerosol validation, NASA LaRC’s
HSRL and the NASA Ames’ Airborne Tracking Sunphotomer (AATS) instrument are
planned to under fly CALIPSO along the east coast of the
It is further hoped that flight comparison opportunities will exist during the TCSP mission with CALIPSO. Obtaining correlative measurements of CPL attenuated backscatter at both 532 and 1064 nm over optically thick cirrus is extremely important for the mission. These measurements will be helpful for verifying whether spectral dependence between the two wavelengths is uniform; thereby, permitting the transfer of the calibration from CALIPSO’s 532 nm channel to its 1064 nm channel. Measurements of cloud extinction are also need to evaluate the a priori selection of Sc and corrections for multiple scattering. Simultaneous observations with MAS over clear ocean scenes will provide cross-reference measurements for IIR calibration analysis. Having direct comparisons between aircraft and CALIPSO is highly desirable and, if they do not occur because of a delayed launch, provisions should be made to obtaining these observations. Nevertheless, statistics acquired by CPL, MAS, and the other instruments will still provide meaningful guidance on the spectral dependence of cloud backscatter measurements and input assumptions. To add to these data sets, ground-based mobile lidar facilities sponsored by CNRS and CSA will also begin collecting overpass observations in July and August 2005.
During the first verification phase, comparisons with satellite observations from SAGE II/III will be conducted to verify the magnitude of aerosol extinction in the 30-34 km region, which is used for calibration of the 532 nm channel. These extinction profile measurements will provide one of the first comparison dataset of CALIOP level 2 products in the lower stratosphere where Sa is fairly well-known. Comparisons between IIR and WFC radiances will be intercompared to examine measurement consistency between instruments. These datasets will also be compared against climatological statistics complied from MODIS observations. As time permits, comparisons between concurrent MODIS (aerosol/cloud) and IIR/WFC/lidar products will be conducted.
Comparison opportunities will also be initiated with the QPQ team soon after the payload begins routine operations. Because of limited coincidences, first comparison activities will be made with reference to climatological records from different sites. As the size of the data set increases (especially in the second phase), comparisons will be made by individual QPQ teams and findings communicated with the CALIPSO Algorithm Team.
A workshop will be held with the CALIPSO Science Team to review the quality of data products and changes to the data handling procedures and retrieval algorithms prior to the initial release of data at L+135 days. Tentative plans based on a June 17, 2005 launch readiness date are to hold this meeting in October 2005.
The primary validation phase
will occur from L+135 days until L+18 months. A sufficient number of
measurements must be acquired and comparison activities completed to support
the release of all CALIPSO products at L+18 months. Comparisons will be made
with correlative measurements acquired from existing ground-based measurement
programs on a Quid Pro Quo basis. Coordination of this effort is being led by
Dr. Tom Kovacs at
A number of complementary field campaigns are also being planned during this phase. A brief list is provided in section 3.3.1. These campaigns will include the coordinated deployment of aircraft, balloon, and ground-based platforms to address scientific questions concerning key issues in atmospheric chemistry, radiation and dynamics. Because many measurements collected during these campaigns will be of considerable value to CALIPSO validation concerns, and conversely as spaceborne measurements are expected to bring valuable complementary contributions, representatives from the science team will actively seek collaboration and support from the different field campaign management teams.
Data comparisons will be
conducted by the CALIPSO science and algorithm teams and with collaborative
measurement groups. A data comparison workshop is planned approximately 15
months after launch to support the major release of Level 2b products.
Improvements to data handling procedures and algorithm retrievals are expected
following this meeting. Revisions to the data sets will be archived at the
Continued monitoring of CALIPSO instrument performance and data product quality will continue as products are regularly archived. Plans are to rely on QPQ data sets and inter-comparison opportunities available during different field measurement programs. Revised data sets will also be assessed and archived at the ASDC.
Launch Readiness June 17, 2005
Initiate Payload Checkout Activities (~ L+7 days ) June 2005
Initiate Laser, IIR, and WFC Instrument Operations (~ L +40 days) July 2005
TC4 Field
CALIPSO specific validation aircraft flights (
CALIPSO specific validation aircraft flights (
CALIPSO specific validation aircraft flights (
Workshop on Level 1 Data Products (October 2005)
Release Preliminary Level 1 Data Products (L+135 days) October 2005
TWP-ICE Field
AGAMES-ASTAR Field
AMMA Field
CIRCLE2 Field
Workshop on Comprehensive Data Comparison (L+15 months) October 2006
Release of Validated Level 1 and 2 Data Products (L+18 months) December 2006
The CALIPSO Principal
Investigator is responsible for the oversight of the mission and validation of
the CALIPSO Science Data Products. The validation effort includes activities by
the CALIPSO Science Team, Project engineers and algorithm development teams and
Correlative Measurement investigators. Activities for assessing the performance
of the CALIOP and WFC instruments will be conducted primarily by the combined mission
operations, project, and science staff at NASA LaRC. The performance assessment for the IIR and
the validation of its Level 1 products is the responsibility of CNES, through
the
To aid in the management of these validation activities, Dr. Chip Trepte will serve as the validation coordinator for US led measurement activities and Dr. Anne Garnier will serve as the validation coordinator for French and other European validation activities. Dr. Tom Kovacs will serve as the primary coordinator of measurement opportunities from existing instrument facilities on a quid pro quo basis. This validation team will also coordinate with CloudSat and other A-Train investigator teams and will seek advice from the ICESAT validation team on techniques and data sets that were profitable in its validation program.
For these activities, the science and validation teams will be organized into working groups and will communicate via email, web links, and telecoms. A data workshop is planned towards the end of the initial assessment period (nominally October 2005). The meeting will be open to external correlative measurement teams.
Dave Winker, PI David.M.Winker@nasa.gov
Jacques Pelon, Co-PI Jacques.Pelon@aero.jussieu.fr
Pat McCormick, Co-PI Pat.McCormick@hamptonu.edu
Chip
Anne Garnier, French Validation Coordinator Anne.Garnier@aerov.jussieu.fr
Tom Kovacs, QPQ Coordinator Tom.Kovacs@hamptonu.edu
CALIPSO Website http://www-calipso.larc.nasa.gov/
CALIPSO QPQ Validation Website http://calipsovalidation.hamptonu.edu/