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calibrater.setsolve - Function

	Package	synthesis
	Module	calibrater
	Tool	calibrater

Arrange to solve for calibration

Synopsis
setsolve(type, t, preavg, phaseonly, refant, table, append, unset)

Arguments

type	in	Component type
		Allowed:	String from 'G','T','B','D','M','MF','K'
t	in	Solution interval (in sec)
		Allowed:	Float
		Default:	60.0
preavg	in	Pre-averaging interval (in sec)
		Allowed:	Float
		Default:	60.0
phaseonly	in	Solve only for phase?
		Allowed:	Bool
		Default:	F
refant	in	Reference antenna. Default is none.
		Allowed:	Int
		Default:	-1
table	in	Output calibration table name
		Allowed:	String
append	in	Append to existing table?
		Allowed:	Bool
		Default:	F
unset	in	If T, unset solve of this type
		Allowed:	Bool
		Default:	F

Returns
Bool

Description

This function specifies the calibration component will be solved for by the solve function. Currently, only one type should be solved for at one time.

Each calibration component represents a separate calibration matrix correction included in the measurement equation. The different types correspond to different instrumental and atmospheric effects. Currently, the solvable calibration components are types 'G','T','B', and 'D', which are antenna-based, and, 'M', 'MF', and 'K' which are baseline-based. Arrange to pre-apply any existing calibration components (of types other than the solved-for one) using the setapply function.

The solution interval t, if > 0.0, specifies the duration of data used for each calibration solution. In general, the solution intervals are measured from the beginning of data segments for each field and spectral window. If t is large enough, a single solution may encompass data from more than one scan or even the whole observation (per field and spectral window). The solution interval represents a coherence time, not an integration time w.r.t. any gaps in the time series; in effect, such gaps are ignored, and the latest time in the solution is never more than t seconds after the earliest time. If t = 0.0, one solution per scan will be computed regardless of the (possibly variable) scan durations. If t = -1, one solution will be obtained for each unique timestamp in the data.

For types B, G, and T, the Measurement Equation is always assumed stationary on the timescale of the solution (t), and so the data are appropriately normalized and automatically averaged within the solution interval before solving. For type D, there are systematic variations (e.g., parallactic angle, P) in Measurement Equation terms (even after pre-applied) on timescales shorter than the expected variation in the D terms. In this case, it is necessary to specify a pre-averaging interval which is shorter than the solution interval. This is done using the preavg parameter, which defaults to 60 seconds.

Supported calibration types:

G

Antenna-based, multiplicative complex gains

B

Antenna-based complex bandpass; a frequency-dependent version of G

T

Antenna-based polarization-independent (tropospheric) gain; a polarization-independent version of G

D

Antenna-based instrumental polarization leakage

M

Baseline-based complex gains (cf, G)

MF

Baseline-based complex bandpass (cf, B)

K

Baseline-based fringe-fitting (phase,delay,delay-rate; currently limited to delays and delay-rates in the central ambiguity)

Pending improvements:

• Fix multi-setsolve (serial) mode
• Improve phase-only mode (per type), internal refant usage
• Add fixed mean gain modulus option
• Enable generalized solution modes, e.g., per-field, etc. (and rationalize t=0 and t=-1 accordingly).

Example

c:=calibrater('3C273XC1.MS');
c.setapply (type='P',t=5.0);
c.setsolve (type='G',t=300.0, refant=3, table='gcal');
c.solve();
c.done();

In this example, analytic (non-solvable) parallactic angle corrections are applied on a 5-second timescale before G solutions are obtained on a timescale of 300 seconds. The resulting solutions are phase-referenced to antenna 3, and stored in a calibration table called 'gcal'.

c.reset();
c.setapply (type='P',t=5.0);
c.setapply (type='G',table='gcal');
c.setsolve (type='D',t=86400.0, preavg=60.0, refant=3, table='dcal');
c.solve();
c.done();

In this example, the solve/apply state of the calibrater tool is reset and then the P and G corrections (from above) are applied before solving for D solutions on a diurnal timescale. Note that the data will be averaged only to 60 seconds before the solution. The resulting D solutions are stored in a table called 'dcal'.