next up previous contents
Next: Recommendations on the observing Up: Observational limitations Previous: Glitches

 

Other effects

Temporal response changes
In some C100 measurements the signal varies on timescale of 10 sec increasing the noise of the measurement. These signal fluctuations seem to be due to temporal response changes. No correction algorithm is currently available.

Chopping offsets
For chopped measurements, any positive or negative signal offset in the off-position causes a virtual difference signal. Such systematic difference signals have been observed and are likely due to inhomogeneities in the instrument's field of view. All chopped observations are probably affected by this effect. Calibration observations have been performed and are being analysed in order to determine correction factors to be included in the off-line data processing.

Flatfield accuracy
A good flatfield correction for the C100 and C200 arrays is necessary to determine the noise level of the background. The accuracy of the flatfield becomes important when difference signals are determined among individual pixels. It is also important in case a map is created from several (raster) pointings. Individual drift behaviour for the different pixels may increase the flatfield uncertainty.



R.J. Laureijs, P. Abraham, U. Herbstmeier, U. Klaas, T. Muller, and the ISOPHOT Instrument Dedicated Team
Fri Aug 30 16:17:39 MET DST 1996