IRAS Explanatory Supplement
X. The Formats of the IRAS Catalogs and Atlases
Appendix X.4 Zodiacal Observation History File (ZOHF) Format


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The ZOHF is a low-resolution version of the entire IRAS sky survey. The average of all detectors within a band produced a ½" wide fan beam which was then boxcar averaged for eight seconds to produce a 30" × 32" beam. Pointing information was similarly averaged over eight seconds to accompany the infrared data. The data base is time ordered and retains the subdivision of the original survey into semi-daily Satellite Operation Programs (SOP) and individual continuous survey scan observaatons (OBS).

Database Organization:

The ZOHF is organized into 572 files, with two consecutive file marks after the last file on each tape. There is one SOP per file starting with SOP 29, i.e. file 1 corresponds to SOP 29, and file 572 to SOP 600. Within a file, each 80-byte logical record contains the timing, pointing and infrared data for a single eight-second average. Each logical record is identified with an OBS, but OBSs are not othervise separated from one another within a SOP ffie. SOPs for which no survey data exist contain one dummy record which has a valid SOP number but zeros in all other fields. The ZOHF is available only as an ulabelled ASCII formatted magnetic tape. The logical record length is 80 bytes with a physical blcck size of 200 logical records or 16000 bytes. The approximate size of the data base is 96 Mbytes. All of the fields contain data. There are no header or trailer records.

Format of ZOHF
Table X.Ap.1
bytenamedescriptionunitstype
1NSOPSOP number--I3
4NOBSOBS number --I3
7NUTCSITime UTCSsec I10
17INCLInclination degreesF6.2
23ELONG 2solar Elongation degreesF6.2
29BETAEcliptic LatitudedegreesF6.2
35LAMBDAEcliptic LonngitudedegreesF6.2
41(X)v112 µm Brightness DensityJy sr-1E10.4
51(X)v225 µm Brightness DensityJy sr-1E10.4
61(X)v360 µm Brightness DensityJy sr-1E10.4
71(X)v4100 µm Brightness Density Jy sr-1E10.4
  1. UTCS is elapsed time in seconds since 0 hours UT, 1 Jan 1981

  2. Elongation is the angle between the line of sight and the Sun. Inclination is the angle between the eclipatc plane and the plane containing the Earth, Sun, and observation direction (i.e., the azimuth angle about the Earth-Sun axis). Elongation was fixed in each OBS, and inclination increased at a constant rate. These angles are related to geocentric ecliptic coordinates by the following expressions:

    cos(ELONG) = cos(X) cos(X - X)

    sin(INCL) = sin(X)/sin(ELONG)

    where (X) is the ecliptic longitude of the Sun.

  3. Conversion from in-band brightness to brightness density assumes a source with an energy distribution which is flat in flux per unit octave as explained in Section VI.C.

Table of Missing SOPs 1
Table X.Ap4.2
053258 264 598
054259 442
055260 594
056261 595
058262 596
200263 597
  1. A dummy data record consists of a valid SOP number and zeros in all other data fields.

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