larger largest
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Figure IV.D.1 The response of the individual detectors to the>
internal refernece source compated to that from the planetary
nebula NGC6543 at 25 µm. The results from all the
25 µm detectors were combined after normalization to the
mean response over the duration of the mission. larger largest |
During the course of the entire mission, the stability of the internal reference source as monitored at least daily relative to the planetary nebula NGC6543. The result of this monitoring program at 25 µm for a large fraction of the mission are shown in Fig. IV.D.1. Let Ri,t be, for detector i and time t, the ratio of the amplitudes from the a flash of the internal reference source and from a scan over NGC6543. If <Ri,j> is the mean ratio averaged over the duration of the mission, the quantity
Yi,t = (Ri,t/<Ri,t> - 1)
is a direct measure of the stability of the internal reference
source since the infrared output from NGC6543 can be presumed
to be stable. The quantity Yi,t is shown as the ordinate in Fig.
IV.D.1 for all full-size detectors in the 25 µm band as a function
of time from the star to the end of the mission. This wavelength
band was selected for presentation since the signal-to-noise ratios
for both the simulator flashes and NGC6543 were the highest in
this band. The dispersion in the measurements at 25 µm is 1.6%,
well within the expected dispersion because of measurement uncertainties.
The measurements in the 12, 60 and 100 µm bands give dispersions
of 2.6, 1.7 and 2.7% respectively. The stability of the internal
reference source is thus better than 2% throughout the mission.
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