The Digitized Sky Survey (DSS) is a ground-based imaging survey of the entire sky in several colors. The survey, performed with Palomar and UK Schmidt telescopes, produced photographic plates that were later digitized at the Space Telescope Science Institute (STScI) to produce the Hubble Guide Stars Catalog (GSC).
Each plate produced by the Survey covers 6.5 x 6.5 degrees of the sky, and the plates have been digitized using a modified PDS microdensitometer. The digital images have a pixel size of either 25 microns (1.7 arcsec per pixel) or 15 microns (1.0 arcsec per pixel), and are 14000 x 14000 or 23040 x 23040 pixels per side. The images are stored on 12-inch optical media and are difficult to access quickly.
This new generation of IRAS images, called IRIS, benefits from better zodiacal light subtraction, calibration and zero levels compatible with DIRBE, and better destriping. At 100 microns, the IRIS product is also a significant improvement over the Schlegel et al. (1998) maps. IRIS keeps the full ISSA resolution, includes well calibrated point sources, and the diffuse emission calibration at scales smaller than 1 degree was corrected for the variation of the IRAS detector responsivity with scale and brightness. The uncertainty on the IRIS calibration and zero levels is dominated by the uncertainty of the DIRBE calibration and the accuracy of the zodiacal light model.
