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.

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