Directory structure¶

This package is agnostic to the arrangement of model data; it simply fetches and processes URLs. Here we document the directory structure adopted for the MeerKAT telescope, both as a suggestion for other telescopes and for users who wish to explore the available models.

Models are arranged in three levels, connected by alias files:

The models themselves are stored as model_type/fixed/sha256_hash.h5, where model_type is the value stored in the HDF5 model_type attribute.
For each configuration of each target (see Concepts), the current model is pointed to by model_type/config/target/config.alias.
For each target, the alias for the current configuration is pointed to by model_type/current/target.alias.

The target may contain multiple components separated by slashes. It may also be empty for telescope-level models, in which case the level 2 alias becomes model_type/config/config.alias and the level 3 alias becomes model_type/current.alias. The config is intended to be a flat version string for the configuration. See Telescope state integration for an example of how these aliases point to each other.

Below, we list the naming conventions currently in use for MeerKAT for target and config. Other telescopes will likely use a different configuration management system and need to describe a different range of targets, so are not expected to use the same naming conventions.

RFI mask¶

target: None
config: meerkat

Band mask¶

target: band/nb_ratio=ratio, where band is the single-letter abbreviation for the receiver band (l, s, u or x in MeerKAT) and ratio is the integer ratio between the digitised bandwidth and the output correlator bandwidth. It is 1 for a wideband instrument and larger for narrowband instruments.
config: The document number of the release note for the correlator.

Primary beam¶

target

group/antenna/band, where group is either individual or cohort). The choice is made by the user depending on whether antenna-specific models are desirable or not. Readers that want the most accurate possible models should use individual, while readers that will benefit from having many antennas share the same model should use cohort. For MeerKAT, cohort will ensure that all antennas share the same model, although this will not hold for the MeerKAT Extension as it has heterogeneous dishes. The band is the single-letter abbreviation for the receiver band (l, s, u or x).

Additionally, for each cohort there is a target cohort/cohort/band. For MeerKAT the cohort name is simply meerkat. For the new dishes in the MeerKAT Extension it will be meerkat_extension.

Note that even if individual is requested, many or all of the antennas may still share the same model if per-antenna models have not been produced.

The current/ directory must contain all the targets defined above, but the config/ directory need not.

config

TBD. For cohorts it is assumed that the average beam properties will not change significantly over time, so an unversioned name (such as meerkat) may suffice. For antenna-specific models the receiver serial number should be included, as well as some form of version number that can be updated for changes not related to the receiver identity.