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3.15 Detector responsivity PHT-C

synopsis: (1) statistical uncertainty in the responsivity from statistical uncertainty in the FCS signal (2) systematic uncertainty from a systematic uncertainty in the FCS signal (due to transients) (3) systematic uncertainty from statistical uncertainties in the illumination matrix (see sect. 3.18) (4) systematic uncertainty from the filter-to-filter response correction (see sect 3.19).

limitations and applicability:
(1) In case no valid FCS measurement is present, a default responsivity is applied, see sect. 3.16.

description:
The FCS measurement is used to determine the responsivity of each pixel R(i) for the filter in which the FCS measurement is taken:

$\begin{displaymath} R(i) = \frac {\langle s_{FCS}(i,f) \rangle \cdot C_{det}} {P_{FCS}(p,f) \cdot {\Gamma}(i,f) \cdot {\chi}(i,f)}~~~A/W, \end{displaymath}$

(3)

where

f indicates the filter, i the pixel number,
$\langle s_{FCS}(i,f) \rangle$ is the FCS signal per chopper plateau,
C_det is the detector capacitance,
P_FCS(p,f) is the in-band power (in W) for a given FCS heating power p,
${\Gamma}(i,f)$ is the illumination matrix, and
${\chi}(i,f)$ is the correction matrix characterizing the filter dependent flat-field variations.

The illumination matrix ${\Gamma}(i,f)$ is needed to correct for the fact that the FCS illumination is not flat but varies from pixel to pixel in the C100 and C200 arrays. The detector flat field correction is necessary to obtain the same responsivity for each filter of the same detector.

purpose correction:
Determination of the responsivity of the C100 and C200 detector array, which is necessary to perform the flux calibration of each filter measurement.

uncertainty/noise introduced:
(1) The mean signal of an FCS measurement has a statistical uncertainty which propagates into the uncertainty of the responsivity. This error will contribute to the systematic uncertainty of the sky measurement(s). (2) the photometric bias propagates in the responsivity determination. (3) the illumination matrix is accurate to within 3% per pixel. (4) the detector flat field correction is accurate to within 5% from filter-to-filter.

auxillary data: none

Next: 3.16 Default detector responsivity Up: 3. Derive SPD level Previous: 3.14 Detector responsivity PHT-P

ISOPHOT Error Budgets: Derive_SPD Processing Steps, Version 1.0, SAI/98-091/Dc