ISCCP CATALOG OF DATA AND PRODUCTS Section 3.2

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3.2 METEOSAT

The European geostationary satellite series, METEOSAT, operated since November 15, 1995 by EUMETSAT (previously operated by the European Space Agency (ESA)), provides data which are used to produce one of the many B1 formatted products for the ISCCP.

A-level data, currently ingested from METEOSAT-7 (prime mission at 0 degrees) and METEOSAT-5 (INDOEX mission at 63 E), consist of data from three spectral channels: visible (0.5-0.9 microns), water vapor (5.7-7.1 microns) and infrared (10.5-12.5 microns). The visible channel has 2.5 km x 2.5 km pixels at the sub-satellite point. The infrared and water vapor channels have 5 km x 5 km pixels at the sub-satellite point. One full disk image in all three channels is recorded every half hour. The raw data from each spectral channel is represented in eight bits (0-255) per pixel.

The raw data, received directly from the satellite, are received in multiplexed form, so initially, these data have to be demultiplexed into separate line-by-line visible, infrared and water vapor image scan lines. A quality control check for missing scan lines and other anomalies is also performed, and the data are further processed (see below) and also archived.

The next stage of the processing consists of computing the deformation parameters by determining the position of the center of the earth's disk in image space using horizon detection techniques. The images are then resampled into rectified image format so that data from all three channels are co-located and lines and pixels are always related to the same latitude/longitude on the earth. The rectified images are used as input to the ISCCP data processing algorithms as pixel navigation is much easier. No calibration factors are applied to the infrared or water vapor data during the processing.

The visible pixels are first averaged linearly to a 5 km x 5 km resolution, to match the infrared and water vapor pixels. Then, every other pixel along every other scan line is sampled to produce a B1-data image.

Various header data are then appended to the data at this stage. All three channel data are processed to B1 format at three-hourly intervals (nominally 0000, 0300, 0600, 0900, 1200, 1500, 1800, 2100 UTC). The B1-data sets are also archived, and are retrieved at intervals and written to IBM 3480 cartridges, each containing four days of data. If no data were available for one of the scheduled times, data collected 30 minutes earlier were substituted. These B1 data are shipped to the ICA on a monthly basis.