2.2.1.0 calibrater.setsolve

calibrater.setsolve - Function

2.2.1 Arrange to solve for calibration
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’ and ’MF’, 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 Jones 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 Jones 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.

Pending improvements:

Allow for incremental solve in one type
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).

Arguments


Inputs
type	Component type
	allowed:	string
	Default:	G T B D M MF
t	Solution interval (in sec)
	allowed:	double
	Default:	60.0
table	Output calibration table name
	allowed:	string
	Default:
preavg	Pre-averaging interval (in sec)
	allowed:	double
	Default:	-1.0
phaseonly	Solve only for phase?
	allowed:	bool
	Default:	false
refant	Reference antenna. Default is none.
	allowed:	int
	Default:	-1
append	Append to existing table?
	allowed:	bool
	Default:	false
cfcache	Name of the directory to be used as a disk cache for convolution functions used to solve for EP-Jones type. Default is blank (i.e., should produce an error).
	allowed:	string
	Default:
painc	Parallactic Angle increment - relavent only for EP-Jones type. A change in the parallactic angle by more than this value will trigger computation of a new convolution function (which will then be cached in the cfcache directory.
	allowed:	double
	Default:	360.0

Returns
bool

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’.

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