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During the 10-month lifetime of IRAS, roughly 40% of the observing time was
devoted to pointed observations, also commonly called Additional Observations
(AOs). The released POs total 7326. Targets were selected from the
following categories: active galaxies; bright stars; close galaxies;
comets; deep fields; molecular clouds; Galactic structure; or Solar system.
May observations were also characterized as 'filler' or sky-survey
follow-ups. The pointed observations were made using well-defined
command sequences, or macros, the most commonly used being the DPS macro
which produced scans at half the survey rate and increased the SNR by
factors ranging from 3.5 to 7.7 depending on the number of scans and the
area covered. A typical observation took about 15 minutes.
The data product resulting from a single PO is a "deep sky grid" consisting of eight images representing the signal and the noise in each of the four IRAS wavelength bands; each image is contained in a separate FITS file. There are two kinds of grids for each observation: FLUX mode and INTENSITY (INTN) mode grids. For the FLUX grids, the data are filtered with a zero-sum bandpass filter centered on the point source spatial frequency; the extended emission is suppressed. INTENSITY grids are spatially smoothed but not bandpass filtered. For further details, including a discussion of the uncertainties, the reader is referred to the User's Guide to IRAS Pointed Observation Products (PDF). Reference: Version and release date: 1.0, 1985 Oct 25 |