Data Format for the NOAO Mosaic

NOAO is building a large format (8K×8K pixels) camera using a mosaic of eight 2048×4096 CCDs with eight amplifier readouts initially, and eventually up to 16. This paper outlines the data format and keyword definition methodology for data from this instrument. The software system is described in other papers (see Tody 1997; Valdes 1997). 1. The Data File Structure NOAO CCD Mosaic data is stored as a single FITS file for each observation. The FITS file contains a primary header with no associated data and a number of extensions. The primary header describes the file contents, and contains global keyword information applicable to all extensions. The extensions include the image data from each amplifier, pixel masks, uncertainty arrays, exposure maps, auxiliary tables, etc. The image data extensions are always present, and other information is added during the reductions. Figure 1 shows the data file structure, and illustrates how the inheritance convention (Zarate & Greenfield 1995) defines the header for each image extension as the combination of the global and individual header keywords.