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3.13 Determination of in-band power from FCS

synopsis:  (1) residual photometric bias of better than 5-15% from the photometric accuracy of the celestial standards, (2) residual systematic uncertainty better than 5% from the statistical uncertainty in the calibration observations. This only holds when the sky signal is close to the FCS signal, otherwise signal non-linearities become the dominant source of uncertainty.

limitations and applicability:
(1) The heating power of the FCS should be within the `soft' limits, the heating powers which have been used for comparison with the celestial standards are within these limits. Outside these limits the photometric bias can be higher than 15% due to uncertainties in the extrapolation. (2) For the aperture photometer PHT-P the inband power is normalized to the area in mm2, the normalisation is based on a standard aperture. (3) For the camera arrays, the inband power given is per pixel.

description:
Based on the electrical heating power applied to the FCS, the power on the detector is obtained from the FCS calibration tables.

purpose correction:
Determination of the flux from the photometric reference (FCS) for a given electical power. This flux is used to calibrate all sky measurements The calibration table has been obtained from the comparison between the FCS signal for a given FCS electrical power with the signal from a calibration standard (calibration star, planet, or asteroid).

uncertainty/noise introduced:
The uncertainties in the FCS tables include the statistical uncertainty from the calibration observations, as well as systematic uncertainties in the predicted fluxes of the calibration target. All uncertainties in the FCS tables add up to the photometric bias of a given observation.

auxillary data:
Cal-G files PP1FCSPOW, PP2FCSPOW, PP3FCSPOW, PC1FCSPOW, PC2FCSPOW
no uncertainties are supplied in the Cal G file.

keyword(s):
CALFCS: FCS used for cal calculations SPD header
RAMPPCT: percentage of ramps used for signal average SPD header
RAMPUSET: percentage of time used for signal average SPD header


next up previous contents
Next: 3.14 Detector responsivity PHT-P Up: 3. Derive SPD level Previous: 3.12 Chopper vignetting/offset correction
ISOPHOT Error Budgets: Derive_SPD Processing Steps, Version 1.0, SAI/98-091/Dc