II.C. Product Description

ISSA Explanatory Supplement
II. IRAS SKY SURVEY ATLAS OVERVIEW
C. Product Description

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Figure II.C.1 ISSA Fields for || > 50° in Equatorial Coordinates
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ISSA, combined with the ISSA Reject Set, is a set of 430 machine-readable images in Flexible Image Transport System (FITS) format (Wells et al 1981). Each image consists of 500× 500 pixels covering a 12.5°× 12.5° field of sky with a pixel size of 1.5'. The fields are along declination bands which are spaced 10° apart. In right ascension, the spacing varies due to convergence at the poles. Field numbering starts at the south equatorial pole as shown in Figures II.C.1 - II.C.3. Note that the numbering scheme is different from the SkyFlux fields. Appendix A lists the entire ISSA and ISSA Reject Set with corresponding field centers.

Figure II.C.2 ISSA Fields for || > 20° in Equatorial Coordinates
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For each field and IRAS wavelength (12, 25, 60 and 100 µm), there is an intensity image for each confirming coverage (HCON-1, HCON-2 and HCON-3) plus a co-added image of all the coverages. Coverage and standard deviation images were also produced and are available upon request at IPAC.

Figure II.C.3 ISSA Reject Fields ||<20° in Equatorial Coordinates
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The FITS intensity images are either 16 or 32 bits per sample. The number of bits per sample was determined by examining the intensity range and comparing it to 5% of median noise, where noise is the standard deviation of the mean of each pixel. If 16 bits is too small to hold the intensity range down to the 5% of median noise level, then the number of bits that will carry information down to that threshold is used. In FITS-formatted images, any number greater than 16 bits requires 32 bits per sample.

The size of each intensity image is either 0.5 or 1.0 Mbytes, depending on noise level and dynamic range of signal. The entire set of ISSA plus ISSA Reject images has a size of 4.2 Gbytes. The ISSA Reject Set comprises about 1.4 Gbytes.

ISSA is available on permanent media through: 

       Coordinated Request and User Support Office (CRUSO)
       NASA/GSFC
       Code 633.4
       Greenbelt, MD 20771.
[NOTE: All released IRAS data products are available from IRSA.]

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