All LBA data correlated at Curtin since 1 January 2010 do not have SEFD amplitude scaling applied at the correlator. This also coincides with providing output data in FITS-IDI format by default, rather than RPFITS as was previously the default.
For all data correlated since 1 January 2010, it is important to run AIPS task
ACCOR as in some versions of DiFX used for production, the amplitude scaling for LBA data formats and/or zoom bands is incorrect. (Note that zoom bands must have been used for correlation of any observation with mixed bandwidth recording). Even if the scaling is OK, then
ACCOR should still be run for 2 bit data to compensate for imperfect sampler statistics. This should be done as a first step before any other calibration.
For optimal weighting of the data in AIPS a priori amplitude calibration should normally be applied before fringe fitting.
For any particular LBA dataset, there are several possible strategies for amplitude calibration, depending on the level of accuracy required.
CLCOR: run once for each antenna with
CLCORPRM(1)set to the square root of the nominal SEFD.
APCAL. More detailed instructions can be found here. The measured Tsys values should be inspected as sometimes there are problems with the logs (e.g. if amplitude variations are made worse by applying the “corrections”, you should worry). The availability and quality of measured Tsys is generally poor, especially at the present time as new backends are being employed at many telescopes and currently have limited ability for Tsys monitoring.
ACFIT, to generate an
SNtable which contains the relative gains of the antennas as a function of time.