The Along Track Scanning Radiometer consists of an Infra-Red Radiometer (IRR) and a Microwave Sounder (MWS). On board ERS-1 the IRR is a four-channel infra-red radiometer used for measuring sea-surface temperatures (SST) and cloud-top temperatures, whereas on board ERS-2 the IRR is equipped with additional visible channels for vegetation monitoring.
To help users familiarise themselves with ATSR-2 and start using data products, the ATSR-1/-2 User Guide is available as a PDF download. This should be read in conjunction with the AATSR Handbook and the document on Envisat-style products for ATSR-1 and ATSR-2 data. An FAQ on ATSR images is available here.