Metafits files

The MWA tracks observation metadata with "metafits" files. Often these accompany the raw visibilities in a download, but these could be old (such as the "PPD metafits" files). hyperdrive does not support PPD metafits files; only new metafits files should be used.

This command downloads a new metafits file for the specified observation ID:

Download MWA metafits file

OBSID=1090008640; wget "http://ws.mwatelescope.org/metadata/fits?obs_id=${OBSID}" -O "${OBSID}".metafits

Why should I use a metafits file?

Measurement sets and uvfits files do not contain MWA-specific information, particularly dead dipole information. Calibration should perform better when dead dipoles are taken into account. Measurement sets and uvfits file may also lack dipole delay information.

Why are new metafits files better?

The database of MWA metadata can change over time for observations conducted even many years ago, and the engineering team may decide that some tiles/dipoles for some observations should be retroactively flagged, or that digital gains were wrong, etc. In addition, older metafits files may not have all the metadata that is required to be present by mwalib, which is used by hyperdrive when reading metafits files.

Controlling dipole gains

If the "TILEDATA" HDU of a metafits contains a "DipAmps" column, each row containing 16 double-precision values for bowties in the M&C order, these are used as the dipole gains in beam calculations. If the "DipAmps" column isn't available, the default behaviour is to use gains of 1.0 for all dipoles, except those that have delays of 32 in the "Delays" column (they will have a gain of 0.0, and are considered dead).