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Basic Information on smamfcal
Task: smamfcal
Purpose: Multifrequency antenna and passband calibration.
Categories: calibration
SmaMfCal is a Miriad task which determines calibration corrections
(antenna gains, delay terms and passband shapes) from a
multi-frequency observation. The delays and passband are
determined from an average of all the selected data. The gains
are worked out periodically depending upon the user
selected interval. SmaMfcal implements algothrims for weighting,
continuum vector normalization, and moving smooth prior to solving
for bandpass and gains, which are necessary for handling data
at submillimeter wavelength when the S/N is poor and phase dispersion
is large. The basic solving algorithms are the same as in Mfcal.
Key: vis
Input visibility data file. No default. This can (indeed should)
contain multiple channels and spectral windows. The frequency
set-up can vary with time.
Key: line
Standard line parameter, with standard defaults.
Key: edge
The number of channels, at the edges of each spectral window, that
are to be dropped. Either one or two numbers can be given, being the
number of channels at the start and end of each spectral window to be
dropped. If only one number is given, then this number of channels
is dropped from both the start and end. The default value is 0.
Key: select
Standard uv selection. Default is all data.
Key: flux
Three numbers, giving the source flux, the reference frequency
(in GHz) and the source spectral index. The flux and spectral index
are at the reference frequency. If not values are given, then SmaMFCAL
checks whether the source is one of its known sources, and uses the
appropriate flux variation with frequency. Otherwise the default flux
is determined so that the rms gain amplitude is 1, and the default
spectral index is 0. The default reference frequency is the mean of
the frequencies in the input data. Also see the `oldflux' option.
Key: refant
The reference antenna. Default is 3. The reference antenna needs
to be present throughout the observation. Any solution intervals
where the reference antenna is missing are discarded.
Key: minants
The minimum number of antennae that must be present before a
solution is attempted. Default is 2.
Key: interval
This gives one or two numbers, both given in minutes, both being
used to determine the extents of the gains calibration solution
interval. The first gives the max length of a solution interval. The
second gives the max gap size in a solution interval. A new solution
interval is started when either the max times length is exceeded, or a
gap larger than the max gap is encountered. The default max length is
5 minutes, and the max gap size is the same as the max length.
Key: weight
This gives different ways to determine weights (wt) prior to
solving for bandpass:
-1 -> wt = 1; the same weighting method as used in MFCAL.
1 -> wt ~ amp0**2/var(i); for a normalized channel
visibility, the reduced variance is proportional
to amp0**2/var(i), where amp0 is the amplitude
of the pseudo continuum and var(i) is the variance
of visibility for the ith channel.
2 -> wt ~ amp0**4/var(i)**2;
Default is 2 for SMA and -1 for other telescopes.
if you have stable phase, use -1;
if the phase stability is poor, use 1 or 2;
for a larger planet, 2 is recommended.
For antenna gains' solver:
-1 -> wt = 1; the same weight method that is used in MFCAL.
>0 -> wt = 1/var, where var is the visibility variance.
Defualt is 1/var.
Key: options
Extra processing options. Several values can be given, separated by
commas. Minimum match is used. Possible values are:
delay Attempt to solve for the delay parameters. This can
be a large sink of CPU time.
nopassol Do not solve for bandpass shape. In this case if a bandpass
table is present in the visibility data-set, then it will
be applied to the data.
interpolate Interpolate (and extrapolate) via a spline fit (to
the real and imaginary parts) bandpass values for
channels with no solution (because of flagging). If
less than 50% of the channels are unflagged, the
interpolation (extrapolation) is not done and those
channels will not have a bandpass solution
oldflux This causes SmaMFCAL to use a pre-August 1994 ATCA flux
density scale. See the help on oldflux for more
information.
msmooth Do moving average of the uv data (the real and
imaginary parts) using the keyword smooth parameters
specified prior to solving for bandpass.
opolyfit Do least-square fit to the bandpass solutions
(the real and imaginary parts) with an orthogonal
polynomial of degree n which can be given in keyword
polyfit.
wrap Don't unwrap phase while do fit or smooth
the uv data.
averrll In the case of solving for bandpass of dual
polarizations, averrll gives vector average
of rr and ll bandpass solutions; the mean value
is written into the bandpass table for each of rr
and ll.
Key: smooth
This gives three parameters of moving smooth calculation of the
bandpass/gain curves
smooth(1) = K parameter k giving the length 2k+1 of the averaging
interval; default is 3.
smooth(2) = L order of the averaging polynomial l; default is 1.
smooth(3) = P probability P for computing the confidence limits;
default is 0.9.
Key: polyfit
polyfit gives a degree of orthogonal polynomial in least-sqaure
fit to the bandpass/gain curves. Default is 3.
polyfit: 1 (linear), 2 (parabolic), 3 (cubic), ....
Key: tol
Solution convergence tolerance. Default is 0.001.