2.4 Selecting data

 

As explained in section 8.2.14, any flux data for which the Run flag (see table 9.7) is set and that can have an unique wavelength assigned to it is output in the AAR. Therefore some serendipitous data may be present in the AAR. This data may be useless (as in data from a detector array that was insufficiently illuminated).

Therefore all data should be examined, band by band, and any useless data thrown away.

Examples of data that can be considered bad includes data where the flag word SWSPFLAG or SWAAFLAG   (see Table 9.8 for a discussion of it's contents) have:

1

bits 0 and/or 1 (corresponding to FLAG values 1, 2 or 3) set, indicating glitches. Be careful with fast AOT 1's though, as lines may be mistaken for glitches - see section 8.5, ``Glitch removal effects on spectral lines in fast speed AOT1 observations''.

2

bits 2 or 3 (corresponding to FLAG values 4 or 8) set, indicating partly or totally out of limit.

3

bit 5 (corresponding to FLAG value 16) set, indicating no data

4

bits 6, 7 and 8 (corresponding to FLAG value 224) set, indicating multiple order

5

no bits set, indicating no order.

Not all of this data will be in the AAR of OLP V5 or greater.

Users should AND SWSPFLAG/SWAAFLAG with the above values and mask out and data so affected.

Data taken outside band regions should not be trusted. For example, band 1A data beyond 2.6 should not be used. The AOT band associated with a particular line in the AAR file can be obtained from SWAADETN (ref Table 9.12) and masking the order bits in SWAAFLAG and aperture bits in SWAASTAT (ref Tables 9.8 and 9.7). If the wavelength in SWAAWAVE is outside an AOT band as defined by the detector number/order/aperture combination, the limits of which are given in Table 3.1, then the data should not be trusted. Alternatively, the band identification number for AOT 1's is kept in the SWAALINE field (ref section 9.4.2, ``SWAALINE and SWAASCNT'').

Users should note that prior to OLP V6 photometric check  and dark current  data was included in the AAR and should be thrown away. Both of these are recognisable in the flags, ref tables 9.7 and 9.8. This data is not present in OLP V6 AAR products.