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Performance Verification Phase and Instrument Status on 12 January
Martin Kessler
The aims of the Performance Verification Phase (8 December to 3 February) include:
- global verification of instruments' performance,
- establishment of the core instrumental calibration,
- initial monitoring of instrument and detector stability,
- functional and scientific validation of observing modes (AOTs)
- acquisition of sufficient data for the scientific validation of the pipeline
processing and its products,
- acquisition of sufficient data for initial cross-calibration checks.
Each day is devoted to a single instrument. A detailed plan of operations was established in advance; however, within the four day-cycle it is possible to ``re-plan'' so as to take maximum advantage of results from previous days.
A mid-term review was held at Vilspa on 12 January to summarise the then-current status of instrument performance and to release some of the Observing modes (AOTs) for use during the first weeks of Routine Phase. In summary, the performance of all instruments is affected to varying degrees by ``glitches'' (cosmic particle hits). The glitch rate varies with instrument and with glitch detection algorithm; as an example the long wavelength detector on ISOCAM sees about 1 glitch per second. Glitches primarily increase noise, but in some cases have led to changes in instrument settings (hence responsivity) and recommendations for changes in observing strategy. De-glitching algorithms are being refined using in-flight data for all instruments.
Looking at each instrument in a little more detail:
- ISOCAM: Sensitivities are near nominal and no substantial changes in integration times are expected. There are a number of technical issues, some expected from ground-based testing, that will require changes to observing strategy and may affect on-target times. The following observing modes have been released for use: CAM01 (general observation); CAM03 (beam switching); and CAM04 (spectral observation).
- ISOPHOT: While not yet fully established, sensitivities are expected to be close to nominal and any changes in observing times are expected to be small. The following observing modes have been released for use: PHT03 (multi-filter photometry with PHT-P); PHT40 (spectrophotometry with PHT-S); and PHT32 (C100 only, multi-filter map / line scan).
- LWS: Wavelength calibration of the grating is complete and is very close to ground-based values. Analysis of the data for photometric calibration of the grating is underway. The sensitivities are not yet well established. However, it is clear that, compared to ground values, there has been a loss of sensitivity, probably around a factor of 2, although early estimates were somewhat higher. Work continues to optimise operating conditions and data processing to minimise these losses.
- SWS: The wavelength calibration has been successfully completed and flux calibration is underway. Current estimates of sensitivity show substantial reductions from pre-launch expectations of up to around X 3 - 4; although there is a wide dispersion between the different detector bands. Work is ongoing to optimise operating conditions and data processing. The following observing modes have been released for use: SWS01 (low resolution full grating scan); SWS02 (grating line profile scan); SWS06 (grating scan); and SWS07 (combined Fabry-Pérot/grating scan).
It should be noted that these results represent one frozen moment in the Instrument Teams' continuously developing understanding of in-orbit performance. These figures and conclusions may still change significantly during the coming weeks. More detailed and updated descriptions will be sent out to observers and posted to the WWW ( http://www.cosmos.esa.int/web/iso).
Next: Spacecraft Status
Up: ISO Info No. 8
Previous: Chronology of Events
Kieron Leech
ISO Science Team
Mon Feb 26 15:56:27 MET 1996