The IRAS "raw" scan data are known as CRDD (Calibrated, Reconstructed Detector Data) and the full set of survey CRDD, merged with the pointing information (boresight) is stored at IPAC in the so-called Level 1 Archive. The Level 1 Archive is in FITS (Flexible Image Transport System) group format. The Level 1 Archive data have the most recent calibration (PASS3) and are used for all of IPAC's by-request data products.
Level 1 Archive Plate Scheme
The Level 1 Archive data are scan data stored in FITS group format. Even though group format is a tabular format rather than an image format, the scans are organized into plates. Each Level 1 Archive plate covers a 6.5 degree by 6.5 degree region with the plate centers 5 degrees apart. Each plate contains those survey scans which cross the region defined by the plate boundaries.
The Level 1 Archive FITS Group Format
Each plate consists of a number of detector scans, and each scan consists of a series of position and flux values.
Each Level 1 Archive plate contains a FITS header, followed by a series of group headers, each of which is followed by the actual scan data. The FITS header includes the plate number, right ascension and declination of the plate center. A full listing of the parameters contained in each group header is available.