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Subsections

• 9.3.1 Validated modes in OLP Version 7
• 9.3.2 Photometric Accuracies of Staring Modes

9.3 Status of Scientific Validation of PHT AOTs  

9.3.1 Validated modes in OLP Version 7

The OLP Version 7 validation status per AOT submode is given in Table 9.1. The table also provides an overview of the next steps to further upgrade both validated and non-validated modes and for which OLP version improvements can be expected.

It should be noted that in the case of AOT PHT22 raster maps are only partly scientifically validated. It has been demonstrated that mini-maps give reliable results for faint source photometry. Most of the photometric accuracy numbers presented for faint source measurements of C100 and C200 are based on mini-map photometry. However, in order to validate PHT22 raster maps in general, the following items must be verified before:

• valid results for all different combinations of raster parameters
• conservation of flux regardless of raster parameters and re-gridding algorithm.

These checks are less related to calibration upgrades but more to the establishment of a sufficiently large test data set and inspection of the observations case by case.

In Table 9.2 we list the validated modes per detector sub-system. For completeness we have added the polarisation modes which can only be evaluated interactively using PIA and special FORTRAN routines.

9.3.2 Photometric Accuracies of Staring Modes

The terms absolute accuracy, relative accuracy and reproducibility have been defined in the following context:

• absolute accuracy is the accuracy achieved w.r.t. the reference Photometry, if the filter measurement had a corresponding FCS transfer measurement in the same filter. Hence, the quality of the FCS calibration against celestial standards is directly verified. Note that no calibration accuracy of the reference photometry (models, IRAS) has been taken into account, as this is beyond the scope of this report. A typical order of the absolute accuracy of the reference photometry is 2 - 10%.
• relative (filter-to-filter) accuracy is the accuracy achieved with respect to the reference photometry, if the filter measurement was not performed in the filter in which the FCS calibration was done. Currently, assumptions about the constancy of the responsivity over the full flux range and for all filters, and, related to that relative filter-to-filter correction factors, apply. It has been proven that this is in general not correct, and it is considered that in future OLP versions corrections for non-linearities of the responsivity with the in-band power will be applied. Hence, the relative uncertainty can be much larger than the absolute one in multi-filter measurements with certain source SEDs. The number of suitable test cases performed in multi-filter mode is much smaller than the number of test cases in any of the absolute measurement modes (i.e. with an FCS measurement in the respective filter). The relative filter-to-filter accuracy could only be established for a minor subset with no test case for C200.
• absolute and relative accuracy are assumed to add to the total Photometric uncertainty. In multi-filter measurements with one FCS measurement the absolute measurement uncertainty is subtracted from all measurements in non-FCS filters in order to derive the relative measurement accuracy.
• reproducibility is the relative consistency of measurements repeated several times with the same measurement set-up. It is a measure of the internal stability of the instrument and describes also the current limitations in signal processing.

In summary, the following calibration accuracies have been achieved per detector:

P1:

10% absolute accuracy and 20% relative accuracy for bright sources (> 50 Jy). For fainter sources the absolute accuracy is within 30%.
The relative reproducibility accuracy is 5% for bright sources and 10% for faint sources.

P2:

Better than 15% absolute accuracy and 10% relative accuracy.
The relative reproducibility accuracy is 2% for bright sources and 12% for faint sources.

P3:

15% absolute accuracy and 20% relative accuarcy down to 0.5 Jy. For fainter sources the absolute accuracy is around 30%.
The relative reproducibility accuracy is 7% for bright sources and 7% for faint sources. Under extreme Space Weather conditions and for the very end of the science window the achieved accuracy for faint sources is poorer.

C100:

15% absolute accuracy and 10% relative accuracy down to 0.5 Jy. For fainter fluxes the absolute accuracy in mini-map mode is 30%.
The relative reproducibility accuracy is 3% for bright sources and 20% for faint sources.

C200:

20% absolute accuracy for brighter sources. Note that in array centered mode accuracies are poorer for the 180 and 200 m filters due to an inadequate PSF correction factor. Photometry in these filters has to be corrected in general by 20-30% towards higher flux values. For fainter sources (< 1 Jy) the accuracy achieved in mini-map mode is 30%. There was no suitable test case allowing to judge the relative filter-to-filter accuracy. The investigated test cases of standard stars ( Boo, Dra and Sirius) did not give conclusive results due to their faintness in the C200 range and application of less optimal observing modes.
The relative reproducibility accuracy is around 10% both for bright and faint sources.