IRAS Explanatory Supplement
VI. Flux Reconstruction and Calibration
B. Determination of Relative Flux

1. Overall Procedure to Determine Relative Photometry
2. Photometry of Point Sources and Small Extended Sources
3. Photometry of Extended Emission
1. Determination of F[TFPR]
2. Determination of the TFPR Annual Variation
4. Problems
1. Rejected Internal Reference Source Flashes
2. Radiation
3. Photon Induced Responsivity Enhancement
1. Point Sources
2. Extended Emission
4. Variation of Frequency Response with Total Flux

The processing outlined above resulted in a current which was assumed to be proportional to the flux incident on the detector except for small effects due to the dwell time on a source. The conversion of the current to relative flux was effected by a comparison of source amplitudes with amplitudes resulting from flashes from the internal reference source (see Section II.C.3) which provided a secondary relative calibration source. The internal reference source was in turn absolutely calibrated with respect to celestial sources using NGC 6543 as a secondary transfer standard; see Section VI.C below. The processing to obtain the relative photometry of the IRAS sources is discussed in this section.