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- 1 Primary HDU
- Extension HDU (Visibilities for timestep/integration 0)
- Extension HDU (Weights for timestep/integration 0)
- Extension HDU (Visibilities for timestep/integration 1)
- Extension HDU (Weights for timestep/integration 1)
- ...
FITS Primary HDU
XTENSIONBITPIX| Keyword | (MWA) Valid Values | Change from v1 format? | Notes |
|---|---|---|---|
SIMPLE | T | conforms to FITS standard | |
BITPIX | 8 | array data type | |
NAXIS | 0 | number of array dimensions | |
EXTEND | T | ||
COMMENT | FITS (Flexible Image Transport System) format is defined in 'Astronomy | ||
COMMENT | and Astrophysics', volume 376, page 359; bibcode: 2001A&A...376..359H | ||
CORR_VER | 2 | New | Correlator format version: <missing>= v1 (Ord / Legacy Correlator), 2 = v2 (MWAX Correlator) |
| COMMENT | Visibilities: 1 integration per HDU: [baseline][finechan][pol][r,i] | New | Description of data format for visibility HDUs |
| COMMENT | Weights: 1 integration per HDU: [baseline][pol][weight] | New | Description of data format for weight HDUs |
MARKER | e.g. 0,1,2... n (where n is the final integration/timestep) | Data offset marker of first HDU (all channels should match). The marker increments by 1 per integration/timestep | |
TIME | e.g. 1531077040 | Unix start time of the data in this file | |
MILLITIM | 0-999 | Milliseconds component of TIME | |
PROJID | e.g. G0000 | MWA Project ID | |
OBSID | e.g. 1215112256 | MWA Observation ID (GPS start time of observation) | |
| FINECHAN | 0.2, 0.4, 0.8, 1, 1.6, 2, 3.2, 4, 5, 6.4, 8, 10, 12.8, 16, 20, 25.6, 32, 40, 51.2, 64, 80, 128, 160, 256, 320, 640, 1280 | New | Correlator mode: Fine channel width in kHz |
| NFINECHS | 1-6400 e.g. 128 == 10 kHz fine channels (1280 kHz / 10 kHz) | New | Number of fine channels in each coarse channel |
INTTIME | 0.25, 0.5, 1.0, 2.0, 4.0, 8.0 | Changed (was only 0.5, 1, 2) | Correlator mode: Integration time (s) |
| NINPUTS | (2-n) in increments of 16 (due to xGPU limitation) 256 == 128T 288 == 144T 512 == 256T | New | Number of inputs into the correlation products |
| CORRHOST | e.g. gpubox27 | New (pseudo-hostname used to be in the filename) | Hostname of the correlator server which processed this coarse channel |
| CORRCHAN | 0-N e.g. 0-23 | New (was in filename as part of the gpubox number). Thus number is now in sky frequency order. e.g. CORRCHAN 20 > CORRCHAN 19 when mapped to corresponding sky frequency - e.g 172.8 MHz > 170 MHz | Coarse channel number selected for correlation. |
| MC_IP | v.x.y.z | New | Multicast IP the data was addressed to |
| MC_PORT | nnnnnn | New | Multicast port the data was addressed to |
FITS Extension Visibility ImgHDU
Visibility Header
This HDU represents the visibilities for one coarse channel for one time integration / time step.
| U2S_VER | X.Y.Z | Version of the mwax_u2s program that captured the UDP packets for this observation | |
| CBF_VER | X.Y.Z | Version of the mwax_db2correlate2db program that performed the F and X stage correlation for this observation | |
| DB2F_VER | X.Y.Z | Version of the mwax_db2fits program that wrote this fits file. |
FITS Extension Visibility ImgHDU
Visibility Header
This HDU represents the visibilities for one coarse channel for one time integration / time step.
| Keyword | (MWA) Valid Values | Change from v1 format? | Notes | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
XTENSION | IMAGE | Image Extension created by MWA DataCapture | ||||||||||
BITPIX | -32 | Changed: v1 Pre Oct 2014 = -32 (32 bit float) v1 Post Oct 2014= 32 (32 bit integer) v2 = -32 (32 bit float) | number of bits per data pixel (negative is floating point) | |||||||||
NAXIS | 2 | number of array dimensions | ||||||||||
NAXIS1 | (coarse channel width / fine_chan_width) * pols(xx,xy,yx,yy) * 2 For 10 kHz fine chan: (1280 / 10) * (4) * 2 == 1024 | Changed: was: baselines * pols * 2 | Fine Channels * Polarisations * 2 (real/imag) | |||||||||
NAXIS2 | For 128T = (128*129)/2 = 8256 For 256T = (256*257)/2 = 32896 | Changed: was: fine channels | Baselines | |||||||||
PCOUNT | 0 | number of group parameters | ||||||||||
GCOUNT | 0 | number of groups | ||||||||||
COMMENT | FITS (Flexible Image Transport System) format is defined in 'Astronomy | |||||||||||
COMMENT | and Astrophysics', volume 376, page 359; bibcode: 2001A&A...376..359H | |||||||||||
TIME | e.g. 1531077040 | Unix start time of this HDU | ||||||||||
MILLITIM | 0-999 | Milliseconds component of TIME | ||||||||||
MARKER | e.g. 0,1,2... n (where n is the final time step) | Data offset marker of HDU (all channels should match). The marker increments by 1 per time step | U2S_VER | X.Y.Z | Version of the mwax_u2s program that captured the UDP packets for this observation | CBF_VER | X.Y.Z | Version of the mwax_db2correlate2db program that performed the F and X stage correlation for this observation | DB2F_VER | X.Y.Z | Version of the mwax_db2fits program that wrote this fits file. |
NOTE: there is no BSCALE in the v2 correlator format.
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