Precise global measurements of sea surface temperature (SST) are of great importance for climate research and our ability to model the ocean/ atmosphere. The ATSR instrument is anAnnouncement of Opportunityexperimental package on the ERS-1 satellite, and it is designed to measure global SST with the accuracy levels (better than 0·5 K) that are required by modern climate models. The ATSR instrument's ability to meet its demanding performance objectives depends critically upon a number of novel design features. The way in which these features enable ATSR to achieve its measurement objectives are outlined, and the main tasks of the data processing scheme developed for the U.K. Earth Observation Data Centre are described, including in particular, the ways in which the telemetry data are decoded, the brightness temperature images are geolocated, and the scientific products are derived.