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calibrater.setsolvebandpoly - Function

2.1.1 Specialization of setsolve for polynomial B (bandpass) solving


Description

This function is a specialization of the setsolve method which should be used to arrange for bandpass solving when polynomial solutions for B are desired, e.g., when per-channel SNR on calibrators is too low to obtain a useful sampled bandpass.

Prior to the solution, the visibility data are averaged in time, and the solution is performed for both phase and amplitude.

This method uses most of the same parameters as the generic setsolve, with a few unique additions:

degamp and degphase
The parameters permit specification of the polynomial order to use in amp and phase. Specifying 0 (zero) yields constant solutions.
visnorm
This parameter is used to normalize the assembled spectral data, in a per baseline manner. If set True, this will have the effect of removing any non-frequency-dependent closure errors (e.g., as caused by source structure, or introduced by the instrument) from the data, and should be used with caution. The resulting solutions will be effectively normalized as well. When visnorm=F is used, closure errors in the data (as supplied to the solver) may be visible in the form of offsets between the data and solutions. For bandpass calibration, this is usually ok, as the shape of the bandpass is the most important aspect of the solution. In future this parameter will be generalized and made available for other solve types. (NB: Use of solnorm=True still provides for post-solve normalization of the solutions.)
maskcenter and maskedge
These parameters control how many channels are ignored on-the-fly, at the center and edges of each input spectral window, respectively. To avoid edge channels, it is almost always better to flag these channels directly, or select against them in setdata. Aggressive use of maskedge (large values), will yield polynomial solutions which will tend to diverge at the edges (especially when the polynomial degree is also high), because maskedge does not change the frequency domain of the solutions. Such solutions should be used with caution in subsequent operations. (It is best to avoid use of maskedge.)

The BPOLY solution is performed for both phase and amplitude, and the result will be stored in the same table. The frequency domain of the solutions is limited to only the range of frequencies selected in selectvis. When correcting data with these solutions (for other solves or with correct), only data within this domain will be corrected. Data outside (e.g., edge channels avoided in setdata for the solve), will not be corrected. Therefore, the same (or narrower) channel selection is recommended for all operations using solutions produced by this function and solve().

Note that the combine parmaeter can be used meaningfully with the BPOLY solver. When combine=’spw’, the data from multiple spws will be combined on a common frequency axis, and a single polynomial will be determined spanning them all. This is different than for ordinary sampled ’B’ solutions, for which combine=’spw’ causes the bandpass to be combined on a common channel axis, effectively yielding a mean bandpass for the set of spws.

Arguments





Inputs

table

Output calibration table name

allowed:

string

Default:

append

Append to existing table?

allowed:

bool

Default:

false

t

Solution interval (units optional)

allowed:

any

Default:

variant

combine

Data axes on which to combine solving (scan, spw, and/or field)

allowed:

string

Default:

degamp

Polynomial degree for amplitude solution

allowed:

int

Default:

3

degphase

Polynomial degree for phase solution

allowed:

int

Default:

3

visnorm

Normalize data prior to solution

allowed:

bool

Default:

false

solnorm

Normalize result?

allowed:

bool

Default:

true

maskcenter

Number of channels to avoid in center of each band

allowed:

int

Default:

0

maskedge

Fraction of channels to avoid at each band edge (in %)

allowed:

double

Default:

5.0

refant

Reference antenna

allowed:

any

Default:

variant

Returns
bool

Example

 
 
cb.open(’ngc5921.ms’);  
cb.selectvis(field=’1331*’)  
cb.setsolvebandpoly(table=’bpoly’,degamp=5,degphase=7);  
cb.solve();  
cb.close();  
 
 
In this example, amplitude (degree 5) and phase (degree 7) Chebychev  
polynomial bandpasses are determined using the default parameters.  

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