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Дата индексирования: Mon Apr 11 02:17:46 2016
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Polarisation Handling

The biggest difference between selfcal and gpscal is in the handling of polarisation and dual feeds.

Though selfcal can handle multiple pointings and frequency ranges, it assumes that the antenna gain is independent of feed (i.e. the X and Y gains are the same). It also only handles Stokes-I models (and ignores visibilities that are unrelated to determining Stokes-I).

Task gpscal is intended for telescopes with dual feeds (either linear or circular), such as the ATCA. Indeed, it will fail for other sorts of data.

• gpscal solves for the two feeds either totally independently, or with the constraint that the XY (or RL) phase of an antenna must be constant with time.
• gpscal converts between Stokes parameters and raw polarisations. It can take multiple input models for different Stokes parameters. However, if a model of a particular Stokes parameter is not given, it is assumed to be zero. For example, if you give it models of I, Q and U, but not V, then the source is assumed to have no circular polarisation.
• gpscal uses the antenna polarisation leakage table if this information is present. If it is not present, leakages are assumed to be zero.
• Unlike selfcal, gpscal cannot take models from multiple pointings or from different frequency ranges. All models must correspond to the same pointing and same frequency range.