Data selection falls naturally into two classes: data quality criteria and science analysis selection. Data quality selections depend on such things as the position of the satellite with respect to the radiation belts, the position of the Sun, and telemetry quality. In general, these are standard selections, although they may vary depending on source strength or scientific requirements. Once the data have passed through this process, an image will be displayed, parts of which may be selected for analysis, e.g. the central region of a cluster of galaxies. Some users may want to revise their original data-quality selection, if, for example, the region of interest appears fainter than expected, requiring a relaxation of the selection criteria to increase the number of photons.
A data selector is being written that will operate on the SF and HKF. The location of the Selector in the pipeline is shown in Fig. 2. It will allow data selection on any combination of science and housekeeping parameters using Boolean algebra. It is based on the CHIP data selector written for handling data from BBXRT, a mission which shares many properties with Astro-D. CHIP allows the selection of data based on housekeeping data as well as other non-imaging data. The user will run the Selector on the SF and HKF to produce a filtered science file, FSF. His or her choice will be made by setting data-quality filters, time windows and be based on quick-looks at housekeeping parameters, the spectra and light curves, as well as on image display and interactive image selection using, e.g., SAOIMAGE. The main output of the Selector will be the FSF file containing data ready for analysis by IRAF/PROS or any other generic analysis system. As well as the FSF file, a file containing the filter settings will also be written out, both in the header and in a separate ASCII file, so that users can reproduce their selection. A standard FSF generated using default filter settings will be provided to the user.
Note that until the user runs the Selector and specifies his or her selection criteria, all the information in the original data files is present: only the user decides which data to omit from analysis.