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Knowledgebase: Cycle 4
Are there antenna position problems in data taken between 25th December 2016 and 31st January 2017 and processed before 21st February 2017?
Posted by Mark Lacy, Last modified by Sarah Wood on 01 May 2017 08:51 PM

Data observed from 03 January, 2017 (with DA42) and from 25 December, 2016 (with DA50) until the February 2017 shutdown (31 January 2017), and that was run through either manual or pipeline calibration and imaging prior to 21 February, 2017, will have the wrong antenna positions for these two antennas. The error is about 3mm.

DA50 started being used two days after the antenna move (move occurred 2016-12-25T17:49). DA42 started being used after the antenna move (move occurred 2017-01-02T14:33 ).

Antennas were integrated during marginal weather conditions, and then a baseline run was done on 10 January in quite poor weather conditions, but both human and diagnostic tests did not identify that conditions were not good enough to yield good antenna positions.

On 21 January a baseline run was done in good weather conditions, but there was a failure to update the antenna position files until 21 February.

Users have two options to correct the antenna positions. First, to re-reduce your data using the correct antenna positions, either by re-running the pipeline or by re-running the manual scripts, users should submit a ticket at the ALMA Helpdesk under the "Data Reduction" department requesting the corrected antenna position file. Users should then use these new antenna positions and the script as described in Chapter 5 of the ALMA Science Pipeline User's Guide when re-running the pipeline. For manual reductions, users will receive specific instructions through the ALMA Helpdesk on how to properly correct the antenna positions using the manual reduction script.

Second, users can have their data re-run at the ARCs and have new data products delivered by opening a ticket at the ALMA Helpdesk under the "Data Reduction" department and selecting the "Quality Assurance Level 3 (QA3)" checkbox.

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