ISCCP CATALOG OF DATA AND PRODUCTS Section 1.2

Table of Contents, Acronyms, Previous Section, Next Section

1.2 ISCCP DATA STAGES

Three data stages have been defined to differentiate between raw image radiance data as received from the satellites, reduced volume radiance data and derived cloud parameters. These are described below, along with further subdivisions within each data stage.

Stage A data are full resolution narrow band radiometer image data (taken every three hours for the geostationary satellites and all orbits for the polar satellites). Included in this category are certain satellite orbital navigation (earth location) and calibration (digital counts to radiometric units) parameters.

Within this data category, there are two sub-categories of data which are required for satellite intercalibration and for the development of local climatologies.

(1) AC-Data - Data for satellite intercalibration

These are full resolution visible and infrared image data, with navigation and calibration parameters appended, for geographical areas of about 2000 km x 2000 km. Data for about 60 of these areas are required each year for each satellite, for the purposes of periodically calculating intersatellite normalization parameters (BC-data).

(2) AS-Data - Special full resolution data sets

These are full resolution image data, with navigation and calibration parameters appended, for about 20 pre-defined geographical areas of about 250 km x 250 km for every 3 hours. These data are expected to be used by research groups in the development of local climatologies.

Stage B data are radiometric image data, which have been reduced in volume through a process of averaging and sampling. The data volume reduction is essential to reducing the amount of data to a manageable size.

Within this category, there are six sub-categories of data. Two of these are simply intermediate stages toward the preparation of a global reduced radiance data set.

(1) B1-Data - Nominal 10 km spacing

These are compressed versions of the Stage A data, produced first by averaging the visible radiances to the resolution of the infrared radiances and then sampling the matched resolution radiance pixels to a nominal 10 km spacing (if necessary). The ICA archives the B1-data from all participating spacecraft. However, the NOAA B1-data are retained in the 4 km GAC form for this stage.

(2) B2-Data - Nominal 30 km spacing

These are further compressed versions of the Stage A data, produced by further sampling of the matched resolution B1-data radiance pixels to a nominal 30 km spacing. The B2-data from the NOAA polar orbiting satellites are archived by the ICA.

(3) B3-Data - Globally merged calibrated radiances

These are B2-data which have been normalized to the polar orbiter radiometer responses. These radiance data are retained in satellite coordinates, but placed in a standard format with navigation and calibration information appended. All B3-data are archived by the ICA. Note that when ordering B3-data, users should also order the corresponding BT data (see below) to obtain the latest version of the radiance calibration.

(4) BC-Data - Normalization coefficients

These are coefficients calculated from the AC-data. The BC-data will be used to convert individual satellite-based radiometric data (counts) into SI units of radiance.

(5) BS-Data - Special reduced volume data sets

These are B1-data for a small number of special geographical regions of about 2000 km x 2000 km. These data will be obtained every three hours over periods of approximately four days each month, and are expected to be used in research on cloudiness development on a synoptic scale and in algorithm development for cloud field structure retrievals.

(6) BT-Data - Calibration Look-up Tables

These are calibration look-up tables to convert count values to physical units for each image that ISCCP has processed into the B3 format. Only images which have actually been processed by ISCCP have calibration tables included.

Stage C data are cloud parameters obtained from B3-data and correlative data using an experimental algorithm. The correlative data (CD-data) are used to specify the radiative properties of the surface and atmosphere in the cloud analysis. All cloud parameters (C1 and C2 data) are computed for a standard equal-area grid with approximately 280 km (nominal) spatial resolution. There are two forms of the C data: C1 which has three hour time resolution and C2 which has monthly time resolution. The ICA archives C1 and C2 data. Since the algorithm used to generate Stage C data was experimental, it was later replaced by the Stage D data. Stage C data covered the period from July 1983 through June 1991.

On going research indicated that a number of improvements and refinements of the analysis and reported statistics were possible in the Stage C data. These changes were implemented for processing of data in the period beyond June 1991; all older data will be reprocessed into the newer version. Stage D data are cloud parameters that have been generated using the newer version of the cloud algorithm. Like the C-data, the Stage D data also consist of D1 and D2 data, with the addition of DX data. D1 data are 280 km resolution equal-area grid data reported every three hours, D2 data are 280 km resolution equal-area grid data reported monthly and DX data are 30 km mapped pixels reported every three hours. The ICA archives D1 and D2 data only. DX data are only available from NASA/Langley Research Center.