Cloud and Ocean Remote Sensing Around Africa (CORSA) from the NOAA AVHRR Radiometer (GAC), 1981-1992, from SAI/JRC

The total number of satellite passes is approximately 12000. The time period covered by the data set is from August 1981 to December 1992 with the intention to extend up to present (1995) as data will be purchased. Geographical coverage is from 45 S to 45 N and from 55 E to 30 W. Initially, emphasis has been put on SST for studying coastal upwelling processes in the Northwest African and Benguela upwelling systems in continuation of the SAI/JRC on-going activity on coastal upwelling research, Nykjaer and Van Camp (1994).

In parallel, different studies are carried out for establishing algorithms for cloud optical properties and their validation. The elaboration of this data set is carried out in the frame of the Cloud and Ocean Remote Sensing around Africa project (CORSA). The five channels of the AVHRR are calibrated to 'top of atmosphere' reflectances for the channels 1 and 2 and brightness temperatures for channels 3, 4 and 5 following the recommendations of Kidwell (1991).

Clouds over the ocean are identified using a modified Saunders and Kriebel (1988) approach. For cloud free areas SST is calculated using a classical 'split-window' algorithm from Castagne et al. (1986). After SST the individual images are resampled into weekly and monthly composites maintaining the original 4 km resolution.

Validation of the SST fields are done by comparing to lower resolution data sets such as Comprehensive Ocean- Atmosphere Data Set (COADS), National Meteorological Center SST Data (IGOSS) and Global Ocean Surface Temperature Atlas (GOSTA). To accomodate the need for the reprocessing the data as algorithms evolve, all raw data have been written to an on-line optical file server system. In the processing, intermediate products are not stored but only the weekly and monthly composites are retained.

This reduces the disk storage requirements for the user without sacrificing computational speed. Weekly and monthly composites of SST for one month, ca. 100 satellite passes, are generated in approximately 5 hours on a SUN Sparc 10 workstation. The weekly and monthly composites are stored on the on-line optical server and made available through collaborative agreements with the Joint Research Centre.

Example SST time series can be found on the CEO World Wide Web home page: "ceo.org/".