Basic Information on atfix

Task: atfix
Purpose: Apply various miscellaneous corrections to ATCA visibility data
Categories: uv analysis

        ATFIX performs various miscellaneous offline corrections appropriate
        for ATCA 3mm data. Steps that can be performed are
          Apply gain/elevation effect
          Apply system temperature measurements
          Correct for incorrect baseline length and instrumental phase.
          Correct antenna table (when some antennas were off-line)
 
        NOTE: This task will usually be used very early in the data reduction
        process. It should be used before calibration.

Key: vis
        The names of the input uv data sets. No default.

Key: select
        Standard visibility data selection. See the help on select for
        more information. The default is to select all data.

Key: out
        The name of the output uv data set. No default.

Key: dantpos
        Currently the on-line system uses the antenna locations derived from
        preliminary observations.
        If a higher precision solution for the baseline lengths is available,
        you will want to correct your data to account for this.
 
        This also invokes corrections of known instrumental phase errors.
 
        The inputs are the equatorial coordinate offsets entered in the
        following order (NO checking is done for consistency):
            dantpos = A1,X1,Y1,Z1,A2,X2,Y2,Z2,A3,X3,Y3,Z3,....
        The input values are the antenna number and the three equatorial
        coordinate offsets (entered in units of nanoseconds).  These input
        values are added to the absolute coordinates read from the data.
        Antenna present in the data but not included in the input value
        list are treated as having a zero coordinate offset.
 
        The arcane unit of nanoseconds is used for historical compatibililty.
        Note 1 nanosec = 0.2997 meters.
 
        A collection of parameter files giving the corrections to apply are
        stored in $MIRCAT. These have names of the form "dantpos.yymmdd"
        where "yymmdd" is the date of the start of a new array configuration.
        Baseline corrections are believed to be constant between array
        configurations.
 
        If a data file is present, you can instruct atfix to read this
        directly using the indirect parameter input. For example, to read
        parameters appropriate for a hypothetical array configuration
        starting on 16 October 2002, use
            dantpos=@$MIRCAT/dantpos.021016

Key: tsyscal
        The determines the way that system temperature measurements are
        applied to the visibility data. Usually this will be used
        to make changes to the way system temperature measurements have
        been applied to the data by the on-line system. The default
        is to interpolate values between successive system temperature
        measurements. Possible values
        for this parameter are:
          none        Do not apply any system temperature measurements. If the
                      the measurements were applied on-line, they are undone.
          any         Do nothing. Leave the Tsys calibration as is.
          constant    Apply a constant Tsys between successive Tsys measurements.
                      This is the approach used by the on-line system at 3mm
                      wavelength.
          extrapolate Apply a Tsys value between measurements which accounts
                      for predicted changes in Tsys with elevation and measured
                      weather.
          interpolate Interpolate a Tsys value between measurements which
                      accounts for predicted changes in Tsys with elevation
                      and measured weather. This is the default.

Key: options
        Extra processing options. Several options can be given,
        separated by commas. Minimum match is supported.
          nogainel  This disables applying a instrumental gain/elevation
                    correction to the data. Currently the gains of the
                    antennas are a function of elevation. By default,
                    a correction is made for gain/elevation effects.
          noinst    Do not correct for instrumental baseline effects. By
                    default a phase correction is made for instrumental
                    baseline effects.

Key: array
        One of the flaws in the current ATCA datafiles is that antenna locations
        are not recorded for antennas that are off-line (and hence not producing
        data). While this might not seem a serious flaw, the off-line antennas
        can still cause shadowing. In particular, this was an issue when
        using the 3-antenna system in compact arrays.
 
        By giving a value to this parameter, atfix will fill in any
        antenna locations that are missing from the input visibility file.
        NOTE: This just fills in missing antenna locations, it does not perform
        any flagging of shadowed data.
 
        The value given to this parameter is either an array configuration name
        (e.g. EW352 or 750A) or a list of six station names (e.g. W106 or N3).
        When giving the station names, these must be in the order of the antennas
        (i.e. CA01, CA02, CA03 etc).
 
        NOTE: When antennas are in a shuffled order, or for arrays using
        the north spur, you should generally give the list of station
        names, as the standard array configuration names assume the
        standard antenna order (not the shuffled order).
        If in doubt, see the on-line history of configurations:
          http://www.narrabri.atnf.csiro.au/operations/array_configurations/config_hist.html

Key: gainel
        Optionally specify the gain elevation curve to be used as a polynomial of
        the antenna gain vs zenith angle.
        First parameter is elevation cutoff in degrees below which gain is kept
         constant (default 0, no cutoff)
        Second parameter is number of terms (default 0), followed by the
        coefficients. If one set of coefficients is specified, the same curve
        is used for all antennas. Otherwise specify 6 lots of coefficients, all
        with the same number of terms.
        E.g., 12,2,1,-1e-2,1,-2e-2,1,-3e-2,1,-4e-2,1,-5e-2,1,-6e-2
        The built-in models for 4cm and 3mm vary with antenna based on
        measurements from early 2000's. Default is to select the built in model
        based on frequency (4-12 GHz, or >70GHz). Note the 3mm model has a
        built-in cutoff of 40 degrees.