Image Enhancement Using the IRAS (Infrared Astronomy Satellite) Survey Data

An improved global calibration was derived and image enhancement techniques developed to increase the image quality, sensitivity, and spatial resolution of maps from the Infrared Astronomy Satellite IRAS survey data. These goals were achieved by augmenting and extending GEISHA Groningen Exportable IRAS High-resolution Analysis system. A completely new calibration scheme using the zodiacal light emission as a standard candle has been designed and implemented. This calibration is better suited for smaller spatial frequencies. Comparison of the zodiacal light calibration and that of IPAC IRAS Processing and Analysis, for point sources, gives very satisfactory results 10 at the wavelengths 12, 25, and 60 microns, but a 50 error at 100 microns. Also scans making an angle larger than 5 deg with the plane perpendicular to the line Sun-IRAS cannot be calibrated properly. An iterative least squates ILSQ routine has been prepared that makes it possible to enhance the resolution of an IRAS image to slightly better than 2 arc minutes for most regions of sky. The output of this routine is directly traceable to the input and the method is rather straightforward. Our ILSQ program is ideal for creating large spatial resolution enhanced images, and for checking e.g. maximum entropy results. A spline-smoothed plate system was created as well, consisting of 40 instead of 363 tapes. Images with a resolution of 8 arc minutes can be made using this data base, and because of the low spatial resolution it is feasible to make images of very large sky regions.