Normally GPCAL writes the solutions as a gains table (item `gains') and a polarization leakage table (item `leakage').
GPCAL can handle either dual linear or dual circular feeds. However by default it expects dual linears -- you must use options=circular so switch it to circular mode. Also the terminology in this document is aimed at linears (e.g. we talk of ``XY phase'' -- for dual circulars this is really ``RL phase'').
Note that the user specifies which parameters are to be solved for. In the case of leakages and xyphases, GPCAL will check for the existence of items ``leakage'' and ``gains'' in the input data-set. If present, these will be used as the initial estimates of these parameters. If you are not solving for these parameters, they will be held at there initial value through the solution process. After converging on a solution, and if the xyphase offsets or leakage parameters have been modified, GPCAL will write out their current values to the appropriate items.
Conventions: Unfortunately there has been a number of changes in the `sign conventions' used within Miriad. For a discussion of the conventions, past sign errors and how they affect you, see the memo ``The Sign of Stokes-V, etc'' by Bob Sault.
Initial estimate of the XY phase of each antenna. The default is 0 for all antennas. If the XY phase has not been applied to the data, then it is important that this parameter is set correctly, particularly for the reference antenna.
xyvary The XY phase varies with time. By default the XY phase is assumed to remain constant. qusolve Solve for Q and U fluxes. Good parallactic angle coverage is required for this. oldflux This causes GPCAL to use a pre-August 1994 ATCA flux density scale. See the help on "oldflux" for more information. circular Expect/handle circularly polarised data. nopol Do not solve for the instrumental polarisation leakage characteristics. The default is to solve for the polarisation leakages on all feeds except the X feed of the reference antenna. noxy Do not solve for any XY phase offset. The default is to solve for the XY phase offset on all antennas except for the reference antenna. nopass Do not apply bandpass correction. The default is to apply bandpass correction if possible. This is rarely useful. noamphase Do not solve for the amplitude and phase. The default is to solve for amplitude and phase. This is rarely useful.
The following are options for advanced users, and should be used with caution. Contact Bob Sault for guidance on their applicability.
xyref Solve for the XY phase of the reference antenna. To do this, the source must be linearly polarized and you must have reasonable parallactic angle coverage. This option can be used with ``noxy'', in which case GPCAL solves for the offset of the reference antenna. polref Solve for the instrumental polarization leakage of the X feed on the reference antenna. This can be combined with ``nopol'', in which case GPCAL solves for X feed of the reference antenna only. vsolve Solve for the Stokes-V of the source. This is only possible for linear feeds and a preliminary leakage solution for the observation already exists. This preliminary solution must be formed from a calibrator with known Stokes-V.