1.3.1.0 ms.statwt

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ms.statwt - Function

1.3.1 Set WEIGHT and SIGMA from the scatter of the visibilities

Description

NOT IMPLEMENTED YET.

This function estimates the noise from the scatter of the visibilities, sets SIGMA to it, and WEIGHT to SIGMA**-2.

Ideally the visibilities used to estimate the scatter, as selected by fitspw and fitcorr, should be pure noise. If you know for certain that they are, then setting dorms to True will give the best result. Otherwise, use False (standard sample standard deviation). More robust scatter estimates like the interquartile range or median absolute deviation from the median are not offered because they require sorting by value, which is not possible for complex numbers.

To beat down the noise of the noise estimate, the sample size per estimate can be made larger than a single spw and baseline. (Using combine=’spw’ is to interpolate between spws with line-free channels is recommended when an spw has no line-free channels.) timebin smooths the noise estimate over time. windowtype sets the type of time smoothing.

WEIGHT and SIGMA will not be changed for samples that have fewer than minsamp visibilities. Selected visibilities for which no noise estimate is made will be flagged. Note that minsamp is effectively at least 2 if dorms is False, and 1 if it is True.

Arguments


Inputs
dorms	How the scatter should be estimated (True -> rms, False -> stddev)
	allowed:	bool
	Default:	false
byantenna	How the scatters are solved for (by antenna or by baseline)
	allowed:	bool
	Default:	true
sepacs	If solving by antenna, treat autocorrs separately
	allowed:	bool
	Default:	true
fitspw	Line-free spectral windows (and :channels) to get the scatter from. (” => all)
	allowed:	variant
	Default:	*
fitcorr	Correlations (V, LL, XX, LR, XY, etc.) to get the scatter from. (” => all)
	allowed:	variant
	Default:
combine	Ignore changes in these columns (spw, scan, and/or state) when getting the scatter.
	allowed:	string
	Default:
timebin	Duration of the moving window over which to estimate the scatter. Defaults to 0s, with an effective minimum of 1 integration.
	allowed:	variant
	Default:	0s
minsamp	The minimum number of visibilities for a scatter estimate
	allowed:	int
	Default:	3
field	Fields to reweight, by names or 0-based ids. (” => all)
	allowed:	variant
	Default:
spw	Spectral windows to reweight. (” => all)
	allowed:	variant
	Default:	*
antenna	Select data based on antenna/baseline
	allowed:	any
	Default:	variant
timerange	Select data by time range
	allowed:	string
	Default:
scan	Scan numbers to reweight. (” => all)
	allowed:	variant
	Default:
intent	Scan intents to reweight. (” => all)
	allowed:	string
	Default:
array	Select (sub)array(s) by array ID number
	allowed:	variant
	Default:
correlation	Correlations (LL, XX, LR, XY, etc.) to reweight. (” => all)
	allowed:	string
	Default:
obs	Observation IDs to reweight. (” => all)
	allowed:	string
	Default:
datacolumn	Which data column to calculate the scatter from.
	allowed:	string
	Default:	corrected_data

Returns
bool

Example

  ms.open("multiwin.ms", nomodify=False)
  ms.statwt(fitspw=’0:0~123;145~211,2:124~255’, field=[0], spw=’0,2’)

  In this example the noise estimates are seperately made from and applied
  to spws 0 and 2.

  ms.statwt(fitspw=’0:0~123;145~211,2:124~255’, fitorder=0, field=[0],
            combine=’spw’)
  ms.close()

  This time the estimate for each baseline is made from the line-free channels
  of spws 0 and 2, and applied to all the spws, including 1 (which could be a
  completely line-filled spw).

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