Use Cases and Requirements

Feature Requirements

Functions for interferometric holography and analysis

• Process interferometric holography data from the VLA, ALMA and ngVLA (i.e. OTF-VLA) telescopes to construct PB and aperture maps. Consider far-field (sky source) and near-field (geostationary satellite or terrestrial beacon) sources.
• Use aperture maps and panel layout information to derive screw adjustments per panel.
• Fit for antenna positions (and axis non-intersection terms) from all-sky (multi-source/scan) observations.

Use Cases

• For VLA : Provide a replacement option to the current AIPS analysis pathway for holography and antenna commissioning for the VLA. Process calibrated VLA holography datasets (pointed and OTF), construct aperture maps, and derive 4-point panel screw adjustments to move the surface closer to ideal. Support far-field holography. Use existing (and new) holography test data (with known panel displacements) to verify the code. Solve for antenna positions from all-sky mutli-source/scan observations. Validate by deriving and using astrohack solutions on the physical antenna and confirming correctness in an end-to-end run.
• For ngVLA : Demonstrate the ability to process calibrated VLA-OTF holography datasets to construct aperture maps and panel adjustment information. Use ngVLA antenna geometry and panel layout information to derive focus fits, panel dimension/deformation fits (5-point panel support) with ascii export of results. Use simulated primary beam models with/without intentional panel displacements to verify the software for the ngVLA antenna geometry prior to there being a physical antenna. Support near-field as well as far-field holography.
• For ALMA : Provide a replacement option to the current modified-Gildas analysis pathway for ALMA holography. Process calibrated ALMA OTF holography data (far-field and near-field) to construct aperture maps. Use ALMA panel layout information to derive panel adjustments for the DA, DV and TP antennas. Verify and validate using either existing or new ALMA holography data.
• For CASA/ngCASA : Provide a method to derive Zernicke model fits from aperture maps for later use in imaging with the AWProjection gridding algorithm.
• Technology transfer : -- AIPS -> CASA : Achieve feature transfer from several AIPS tasks (HOLOG, PANEL, LOCIT) to the CASA/ngCASA ecosystem. -- ARDG -> CASA : Incorporate feature/algorithm R&D prototypes into production software : A-Z Solver and Plumber, demonstrated on ALMA, VLA, MeerKAT, GMRT and plan for future support for MeerKAT, GMRT, etc.

Numerical accuracy requirements

TBD

Timeline :

• On-sky tests with an ngVLA antenna, connected with the VLA, in mid 2024
• Validation/Tests to be done in mid-2023 on the VLA and ALMA.