The PSRDADA format is used internally within the MWAX correlator and beamformer components. It is not user-facing.
Pre Correlator
This is the header that is created by mwax_u2s when creating a subfile from the multicast UDP. It therefore describes headers that MWAX VCS users would see in the VCS subfiles.
| Keyword | Valid values or Example | Used By | Description |
|---|---|---|---|
| HDR_SIZE | 4096 | PSRDADA | Required by PSRDADA - size of header in bytes (should always be 4096) |
| POPULATED | 0 | 1 | mwax_db2correlate2db | Used to ensure the correlator does not read an incomplete file. 0 means the file is not yet complete, 1 means the file is ready for consumption |
| OBS_ID | 1244973688 | mwax-db2fits | Obs_id of this observation |
| SUBOBS_ID | 1244973688 | mwax-db2fits | GPS second of this part of the observation. Increments in 8 sec intervals |
| MODE | MWAX_CORRELATOR MWAX_VCS NO_CAPTURE | mwax_db2correlate2db mwax-db2fits | This matches the "mode" from the existing metadata database/schedule. |
| UTC_START | 2018-10-11-05:26:14 | PSRDADA mwax-db2fits | Required by PSRDADA. This is the UTC start date/time of the subobservation(?). Used by mwax-db2fits to append a human readable date/time to the filename produced. |
| OBS_OFFSET | 0 (n seconds since start of observation) | PSRDADA mwax-db2fits | Required by PSRDADA. I believe this is the number of seconds offset from the start of the observation. First subobservation will have this set to 0. Second subobservation will be 8, etc. |
NBIT | 8 | mwax_db2correlate2db | Bits per sample (should always be 8) |
| NPOL | 2 | mwax_db2correlate2db mwax-db2fits | Polarisations per tile (i.e. rf_chains) (should always be 2) |
| NTIMESAMPLES | 64000 | mwax_db2correlate2db | Number of timesamples in each input sub-block of a subobservation (nominally sub-blocks are 50 ms) |
| NINPUTS | 256 | n rfinputs | mwax_db2correlate2db | Number of signal paths present in the input subobservation file, to be correlated (must be <= NINPUTS_XGPU) |
| NINPUTS_XGPU | 256 | n rfinputs in multiples of 16 | mwax_db2correlate2db | Number of signal paths actually correlated by xGPU (must be a multiple of 16; must match the number of paths that xGPU has been configured for) |
APPLY_PATH_WEIGHTS | 0 | 1 | mwax_db2correlate2db | Should scalar path weights be applied prior to correlation (for gain normalisation and/or sub-arraying) |
| APPLY_PATH_DELAYS | 0 | 1 | mwax_db2correlate2db | Should fractional path delays be applied prior to correlation (for phasing up to a correlation pointing centre) |
| APPLY_PATH_PHASE_OFFSETS | 0 | 1 | mwax_db2correlate2db | Should path phase offsets be applied prior to correlation (for fringe-stopping, in conjunction with applying path delays) |
| INT_TIME_MSEC | 200 - 8000 | mwax_db2correlate2db mwax-db2fits | Correlator integration time (milliseconds) |
| FSCRUNCH_FACTOR | 40 (1 - 6400) | mwax_db2correlate2db mwax-db2fits | Correlator frequency scrunch factor: number of ultrafine 200 Hz fine channels to average together |
| APPLY_VIS_WEIGHTS | 0 | 1 | mwax_db2correlate2db | Should data occupancy weights be applied to normalise the output visibilities |
TRANSFER_SIZE | 5275652096 | PSRDADA mwax_db2correlate2db | Total number of bytes of input data for one subobservation (of nominally 8 seconds) |
PROJ_ID | G0008 | mwax-db2fits | Project ID of observation |
| EXPOSURE_SECS | 8 (in incremements of 8 seconds) | mwax-db2fits | Duration of observation in seconds |
| COARSE_CHANNEL | 76 (0 - max receiver channel number == 255) | mwax-db2fits | Receiver channel number |
| CORR_COARSE_CHANNEL | 9 | (1 - coarse channel max) | mwax-db2fits | Correlator channel number - which correlator channel "index" is this? e.g. first channel would be 1. In a 24 channel system, last channel would be 24. This would map to gpubox01-24 in the legacy Correlator |
| SECS_PER_SUBOBS | 8 | mwax_db2correlate2db mwax-db2fits | Number of seconds per subobservation |
UNIXTIME | 1539235574 | mwax-db2fits | Unix time of the start of this observation. This field is used by mwax-db2fits to provide a UNIX timestep for each integration throughout the observation. |
| UNIXTIME_MSEC | 0 | mwax-db2fits | Unix time milliseconds offset of the start of this observation. This will always be 0 with the current setup, but is here for completeness. |
FINE_CHAN_WIDTH_HZ | 10000 | mwax-db2fits | Correlator output fine channel width in Hz |
| NFINE_CHAN | 128 | mwax_db2correlate2db mwax-db2fits | Correlator output number of fine channels |
| BANDWIDTH_HZ | 1280000 | mwax-db2fits | Coarse channel passband width in Hz, i.e. the channel spacing |
SAMPLE_RATE | 1280000 | mwax_db2correlate2db | Sample rate of input data in samples/s (whether critically-sampled or oversampled) |
| MC_IP | 0.0.0.0 | mwax-db2fits | Multicast IP for this coarse channel (for debug purposes) |
| MC_PORT | 0 | mwax-db2fits | Multicast port for this coarse channel (for debug purposes) |
| MWAX_U2S_VER | X.Y.Z | mwax_db2fits | Version number of mwax_u2s used to capture the UDP packets for this subfile |
Post Correlator changes
The below changes are made during the mwax_db2correlate2db process. The only recipient of this updated header is mwax_db2fits, which uses it to produce the output visibility FITS files.
| Keyword | Valid values or Example | Used By | Description |
|---|---|---|---|
NBIT | 32 | mwax-db2fits | Bits per complex visibility component (real | imaginary) |
| NTIMESAMPLES | 1 - 40 (for 8 s subobservations) | ? | Number of integration times (visibility sets produced) per subobservation |
TRANSFER_SIZE | n bytes | mwax-db2fits | Total number of bytes of output data for this 8 second subobservation. Calculated by: bytes = visibilities + weights visibilities = integrations * baselines * fine channels * polarisations * bytes_real * bytes_imaginary weights = integrations * baselines * polarisations * bytes_real |
| MWAX_DB2CORR2DB_VER | X.Y.Z | mwa-db2fits | Version number of the correlator executable used to perform the F and X stages of correlation |