National Radio
Astronomy Observatory

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 m/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 m / (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

Example

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