Correction to the Station Adder in the Long-Baseline pipeline

The Long Baseline (LB) pipeline increases the signal-to-noise ratio for baselines containing international stations by combining all of the core stations into a single "Super" station. This is done by the "Station Adder" in NDPPP.

 

The LB working group found that the Station Adder provides images and/or calibration solutions that are noisier than expected. The cause of this higher noise was identified in an incorrect calculation of the visibilities for the super station: while a weighted sum of the visibilities should be calculated for the output combined visibility, only a simple sum of visibilities is actually calculated by NDPPP. The use of a simple sum instead of a weighted one results in an increase in image noise of about 30%. 

 

A corrected version of NDPPP will be in production (LofIm) on 28 Jul 2015 and will be implemented in the RO pipelines from the next software roll-out, which is currently scheduled in early September 2015. For data sets that have already been processed through the RO pipelines, a script is provided to fix this issue.


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