A new development study has introduced new methods to assess and better schedule the ALMA uv coverage. Applying these methods will improve imaging quality for extended objects.
Contributed by Dirk Petry.
Development study on ALMA uv coverage assessment completed
Published: 31 Aug 2024
Example of the set of diagnostic plots for uv coverage assessment produced by the new uv coverage analysis tool ”assess ms” for an ALMA observation (a mosaic) with some underexposure at long baselines in two sectors but otherwise good uv coverage. First row, left to right: comparison of observed baseline length distribution; 2D filling fraction plot; azimuthal inhomogeneity vs. baseline. Second row: ”flat sensitivity” plot (see text); filling fraction vs. baseline for each of the four sectors; baseline length distributions for each of the mosaic fields overplotted (with the expected shape for best PSF in black).
In August 2024, a team from ESO, JAO, NAOJ, and the University of Vienna completed an ALMA internal development study on "new methods for ALMA beam assessment, scheduling, and shaping". The study had been kicked off by D. Petry, M. Diaz Trigo, R. Kneissl, and I. Toledo in 2020 to investigate several long-standing issues with how ALMA ensures that it fulfills the PIs' requests for sensitivity at given angular scales, in particular the so-called Largest Angular Scale (LAS) that users can specify in the OT.
The study was completed on 28 Aug 2024 and the essential aspects are discussed in two SPIE proceedings papers, Petry et al. 2020 and Petry et al. 2024 (also available on arXiv).
In addition, the final report contains a list of suggestions for improvements in the quality assurance (QA) and scheduling procedures for ALMA and ACA. Furthermore, it describes the prototype uv coverage assessment tool "assess_ms", which was developed during the study and which could be used to monitor the uv coverage in interferometric datasets as part of ALMA quality assurance and to extend the information contained in standard ALMA data deliveries by a set of diagnostic plots characterising the uv coverage and comparing it to the ideal case for best PSF.
The report also contains a first analysis of the uv coverage of Group OUSs, which is relevant to data combination, and will be studied further in the future.
All ALMA development study reports are available from
https://www.eso.org/sci/facilities/alma/development-studies.html