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CERES Aqua Edition1B SFC |
| Investigation: | CERES |
| Data Product: | Monthly Gridded TOA/Surface Fluxes and Clouds (SFC) |
| Data Set: | Aqua (Instruments: CERES-FM3 or CERES-FM4, MODIS) |
| Data Set Version: | Edition1B |
The purpose of this document is to inform users of the accuracy of this data product as determined by the CERES Science Team. The document summarizes user applied revisions (e.g. Rev1), key validation results, provides cautions where users might easily misinterpret the data, provides links to further information about the data product, algorithms, and accuracy, and gives information about planned data improvements. This document also automates registration in order to keep users informed of new validation results, cautions, or improved data sets as they become available.
User applied revisions are a method CERES uses to identify improvements to existing archived data products that are simple for users to implement, and allow correction of data products that would not be possible in the archived versions until the next major reprocessing 1 to 2 years in the future. All revisions applicable to this data set are noted in the section User Applied Revisions to Current Edition.
This document is a high-level summary and represents the minimum information needed by scientific users of this data product. It is strongly suggested that authors, researchers, and reviewers of research papers re-check this document for the latest status before publication of any scientific papers using this data product.
The Monthly Gridded TOA/Surface Fluxes and Clouds (SFC) archival data product contains hourly single scanner flux and cloud parameters averaged over 1.0-degree regions. Input to the SFC Subsystem is the Single Scanner Footprint TOA/Surface Fluxes and Clouds (SSF) archival data product. Each SFC covers a single month of data from a single CERES instrument mounted on one satellite. Individual Aqua Edition1B SFC files contain information for five consecutive latitude bands.
Instantaneous CERES footprint data are sorted by region and time. Gridded means of SSF data are calculated in hourly local solar time increments for each region with at least one CERES observation. These region/time increments are centered on the local half-hour and are referred to as "hourboxes." The major categories of data output on the SFC are as follows:
All CERES footprints with a non-default value of either Shortwave (SW) or Longwave (LW) flux are used in the SFC product. CERES data collected during the Rotating Azimuth Plane (RAP), crosstrack, and the alongtrack scan modes are used.
A full list of parameters on the SFC is contained in the CERES Data Product Catalog (PDF) and a full definition of each parameter will be contained in the SFC Collection Guide (in preparation).
When referring to a CERES data set, please include the satellite name and/or the CERES instrument name, the data set version, and the data product. Multiple files that are identical in all aspects of the filename except for the 6 digit configuration code differ little, if any, scientifically. Users may, therefore, analyze data from the same satellite/instrument, data set version, and data product without regard to configuration code. Depending upon the instrument analyzed, these data sets may be referred to as "CERES Aqua FM3 Edition1B SFC" or "CERES Aqua FM4 Edition1B SFC."
The purpose of User Applied Revisions is to provide the scientific community early access to algorithm improvements which will be included in future Editions of the CERES data products. The intent is to provide users simple algorithms along with a description of how and why they should be applied in order to capture the most significant improvements prior to their introduction in the production processing environment. It is left to the user to apply a revision to data ordered from the Atmospheric Science Data Center. Note: Users should never apply more than one revision. Revisions are independent and the latest, most recent revision to a data set includes all of the identified adjustments.
The CERES Science Team has approved a table of scaling factors which users should apply to the Edition1B SFC parameters.
For the SFC SW TOA Fluxes (Up), users should utilize the following equation:
The SFC SW TOA Fluxes (Up) are listed in the table below:
| SFC TOA SW Flux | SDS Index |
|---|---|
| SW TOA Clear-Sky Flux | SFC-29 |
| SW TOA Total-Sky Flux | SFC-33 |
For the SFC TOA Albedos, users should utilize the following equation:
The SFC TOA Albedos are listed below:
| SFC TOA Albedo | SDS Index |
|---|---|
| ALB TOA Clear-Sky | SFC-32 |
| ALB TOA Total-sky | SFC-36 |
For the SFC Net SW SRF Fluxes, users should utilize the following equation:
The SFC Net SW SRF Fluxes are listed below:
| SFC Net SW SRF Fluxes | SDS Index |
|---|---|
| Net SW SRF Model A Clear-Sky Flux | SFC-40 |
| Net SW SRF Model B Clear-Sky Flux | SFC-44 |
| Net SW SRF Model A Total-sky Flux | SFC-49 |
| Net SW SRF Model B Total-Sky Flux | SFC-53 |
For the SFC SW SRF Fluxes (Down), no correction should be applied, and thus:
The SFC SW SRF Fluxes (Down) are listed below:
| SFC SW SRF Fluxes (Down) | SDS Index |
|---|---|
| SW SRF Model A Clear-Sky Flux | SFC-37 |
| SW SRF Model B Clear-Sky Flux | SFC-42 |
| SW SRF Model A Total-Sky Flux | SFC-46 |
| SW SRF Model B Total-Sky Flux | SFC-51 |
This revision is necessary to account for spectral darkening of the transmissive optics on the CERES SW channels. By March 2005, this darkening has reduced the average global all-sky SW flux measurements by 0.9 and 0.7 percent for Aqua FM3 and FM4 data respectively. A complete description of the physics of this darkening appears in the CERES BDS Quality Summaries under the Expected Reprocessing section. After application of this revision to the Edition1B SFC data set, users should refer to the data as Aqua Edition1B-Rev1 SFC.
There are several cautions and helpful tips that the CERES Science Team notes regarding the use of CERES-Aqua SFC data:
To reduce the effect of electronic crosstalk signals in Window channel measurements induced by high Shortwave (bright) scenes, a bridge balance memory patch was developed and uploaded on September 30, 2004 and unloaded on October 12, 2004. This patch was intended to modify the Window bridge balance set to point to midrange (2048). This patch, however, inadvertently set the bridge balance set points to midrange (2048) for all 3 channels. This reduced the dynamic range for the Total and Shortwave channels leading to saturated radiometric measurements. Saturations typically occurred for the brightest earth-viewing scenes, resulting in data dropout at high radiance values. As a result of this, some regional and zonal monthly mean SW and LW TOA fluxes are biased in October 2004 due to missing fluxes from DCCs. The problem also causes biases in global mean fluxes.
TOA SW data are corrected to a common solar zenith angle (SZA) before averaging in each hourbox. This requires two corrections:
For surface SW fluxes, only the correction based on the change in solar insolation is applied. There is no correction for the change of albedo with SZA.
Mean SW fluxes are calculated for up to 20 ADM scene classes in each hourbox. These scene classes are a function of surface type, cloud amount, cloud phase, and optical depth and are consistent with the ADM types used for producing fluxes from the CERES instrument aboard the Tropical rainfall Measuring Mission (TRMM) (see a discussion of TRMM ADM). These ADM scene classes are different from the ADM classes used to calculate fluxes on the Aqua Edition1B SSF (see the Aqua Edition1B SSF Data Quality Summary). The data are sorted consistently with the TRMM ADM scene classes so that these data can be used with directional models (DRM) of the variation of albedo with solar zenith angle that were developed from TRMM data. These DRM are used to interpolate the measured albedos to unobserved hours of the day during the calculation of the monthly mean SW flux. TRMM data are used for DRM development since the TRMM orbit precesses through all local times and therefore samples the full range of SZA. The sun-synchronous Terra and Aqua orbits do not provide the SZA sampling necessary for ADM and directional model development.
The mean clear-sky flux for each hourbox is calculated using only footprints with cloud amounts less than 0.1%.
The SFC product contains data collected from rotating azimuth (RAP), alongtrack, and crosstrack scanning operating modes. Users can identify hours that include RAP data by checking the viewing zenith angle and relative azimuth angles for default values. These parameters cannot be defined for RAP data. The user can check the scan mode used on a given day by consulting the CERES Operations in Orbit web site.
Users should be careful about comparisons of SFC CERES TOA fluxes with ERBE or ERBE-like fluxes. The geographic location of a CERES flux estimate is at the surface geodetic latitude and longitude of the CERES footprint centroid. On ERBE, all fluxes are located at a geocentric latitude and longitude corresponding to the 30-km level. Other differences are expected due to:
An overview of the ERBE-like/CERES flux differences can be found in the Aqua Edition1B SSF Data Quality Summary.
All CERES footprints with a non-default value of either SW or LW flux have been used as input to the SFC.
The SFC contains gridded means of all data currently available on the SSF product. Users should consult the Aqua Edition1B SSF Data Quality Summary for information concerning the availability and accuracy of individual parameters. For instance, Shortwave Model A surface fluxes are limited to clear-sky footprints. Longwave Model A surface fluxes are also limited to clear-sky footprints. Shortwave Model B and Longwave Model B surface fluxes, however, are available for all-sky.
The User should be aware that the Aqua SFC contains additional aerosol parameters from MODIS that are not included on the TRMM SFC product. This results in a slight change in the read routines.
The User should consult the Aqua Edition1B SSF Data Quality Summary for information on the accuracy of the data used as input to the SFC. There are no known issues with the accuracy of the sorting and gridding of the data to produce the SFC.
An overview of the temporal interpolation and spatial averaging algorithms used for CERES can be found in the following reference:
Young, D. F., P. Minnis. D. R. Doelling, G. G. Gibson, and T. Wong, 1998: Temporal Interpolation Methods for the Clouds and Earth's Radiant Energy System (CERES) Experiment. J. Appl. Meteorol., 37, 572-590.
A CERES Aqua Edition2A dataset is expected to replace this data set in late 2005, once the Aqua based ADM is finalized. The CERES Team will continue detailed examination and documentation of the ground calibration and characterization data, as well as the in-flight calibration opportunities. Notification of any changes will be sent to registered users.
The CERES Team has gone to considerable trouble to remove major errors and to verify the quality and accuracy of this data. Please provide a reference to the following paper when you publish scientific results with the CERES Aqua Edition1B SFC data:
Wielicki, B. A., B. R. Barkstrom, E. F. Harrison, R. B. Lee III, G. L. Smith, and J. E. Cooper, 1996: Clouds and the Earth's Radiant Energy System (CERES): An Earth Observing System Experiment, Bull. Amer. Meteor. Soc., 77, 853-868.
When Langley ASDC data are used in a publication, we request the following acknowledgment be included: "These data were obtained from the NASA Langley Research Center EOSDIS Distributed Active Archive Center."
The Langley ASDC requests two reprints of any published papers or reports which cite the use of data that we have distributed. This will help us determine the use of data that we distribute, which is helpful in optimizing product development. It also helps us to keep our product related references current.
When referring to a CERES product, please include the satellite name (Aqua), the dataset version (Edition1B), and the product name (SFC). In this case use CERES Aqua Edition1B SFC data.
For questions or comments on the CERES Quality Summary, contact the User and Data Services staff at the Atmospheric Science Data Center.
