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imager.sensitivity - Function

2.3.1 Calculate rms sensitivity


Description

NB: The implementation in this function will be removed for CASA v4.5. We now recommend that the im.apparentsens() function be used instead of this one, especially if their weights are initialized and calibrated.

Calculate the point source sensitivity for the selected data, both absolutely and relatively (to that for natural weighting).

To do the calculation, we use the imaging weights (in the column called IMAGING_WEIGHT) as calculated from the WEIGHT column, and an estimate of the effective net bandwidth and integration time. The calculation therefore includes all the effects of weight and filter.

The output is an array with mixed elements. Counting from zero, the second element (out[1]) is the net sensitivity, third element is the ratio of the reduction in sensitivity due to the chosen weighting scheme. This ratio is 1.0 for Natural weight and greater than one for all other weighting schemes. (NOTE: Further testing is required of this value and hence this is kept separate for now).

The sensitivity calculations require Tsys and collecting area of the antenna. These quantities are not known from the MS. The sensitivity is therefore returned in units of Jy mˆ2  /K. Multiplying the second elements with the ration of the Tsys and effective antenna collecting area will give the sensitivity in Jy/beam units.

The fourth elements of the return value is a record with the following keys: ’nbaselines’, ’effectiveintegration’, ’effectivebandwidth’, ’sumwt’ and ’spwid’. These can be used to get the number of baselines used, effective integration time (in sec), the effective bandwidth (in Hz), the sum of weights and the absolute spectral window IDs used.

Arguments





Outputs

pointsource

Calculated point source sensitivity (Jy mˆ2  / (K beam))

allowed:

record

Default:

relative

Calculated relative sensitivity

allowed:

double

Default:

sumweights

Calculated sum of weights

allowed:

double

Default:

senrec

Record per SPW per chan sensitivity calculations

allowed:

record

Default:

Inputs

async

Run asynchronously in the background

allowed:

bool

Default:

false

Returns
bool

Example

 
 
a=im.sensitivity(false);  
print ’Sensitivity =’, a[1];  
print ’Relative to Natural Weighting = ’, a[2];  
 

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