Astrometry correction due to a thermoelastic drift

Rationale

Observations performed at the end of the Solar Aspect Angle (SAA) range (the so-called 'warm' attitude range, SAA in the 110° to 119°.2 interval) could present a degradation of the pointing performance due to thermo-elastic effects. These would include a larger APE and a pointing drift.

We have performed a study on this effect by calculating the Z-axis offset for a set calibration observations. While fot STR2 temperatures below -15C the median offset presents a certain scatter around zero, for higher temperatures the behaviour of the Z-axis offset diverges. We have derived a linear correlation between the STR2 temperature and the Z-axis that aims at correcting the effect of such a thermoelastic drift.

We have developed a script aimed at correcting the astrometry offset produced by the thermoelastic. This should be applied to improve the pointing for observations performed at the 'warm' attitude range (STR2 temperature >-15C).

The script can be found in HIPE under the Scripts menu, in the General Useful scripts section.

Please note that Avoiding observations performed in STR switch-over periods, those indicated in http://herschel.esac.esa.int/twiki/bin/view/Public/StrSwitchOversAndSvvResets

In order to

-- Pilar Esquej - 2016-12-01

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