Well-established/well-used specifications.
Similarity with data obtained with other telescopes/instruments.
Ease of transport/import to other platforms/software packages.
Availability of software tools/utilities, including standalone freeware and software libraries.
The aips++ SDFITS page to read more about SDFITS specifications.
The MAST FITS page at STScI.
The GSFC FITS Support Office.
Bob Garwood's summary talk at ADASS IX.
The FV page to download the generic FITS viewer.
The CFITSIO page to download the C and FORTRAN FITSio routines.
A single data dump occuring every D seconds consists of R spectra where R = S subcorrelators times P polarizations.
A single dumped spectrum contains N spectral points, corresponding to a single subcorrelator unit.
Each of the R spectra is dumped to a separate row of the binary table.
Another way to think of this is that, every D seconds, spectra from all C channels are dumped to disk in R rows containing the records associated with each block of N spectral points. Here C = N spectral points times S subcorrelators times P polarizations.
A single dumped spectrum of N spectral points is written to column 1 of the table as N elements of 4 byte real.
The remaining columns 2-52 occupy 396 bytes. (See below for current column assignments.)
A single row therefore has a width of (N times 4) bytes plus 396 bytes.
Thus a single data dump contains R rows of (4 N + 396) bytes.
| Col# | Title | Description | Format | # bytes |
|---|---|---|---|---|
| 1 | DATA | Actual Data | 1024E | 4096 |
| 2 | OBJECT | Name of source observed | 16A | 16 |
| 3 | TDIM1 | Dimensions of DATA array | 16E | 16 |
| 4 | CTYPE1 | Axis type and Doppler Correction | 8A | 8 |
| 5 | CRVAL1 | Center Frequency | 8D | 8 |
| 6 | CDELT1 | Frequency Interval | 8D | 8 |
| 7 | CRPIX1 | Pixel of Center Frequency | 8D | 8 |
| 8 | CRVAL2 | RA | 8D | 8 |
| 9 | CRVAL3 | DEC | 8D | 8 |
| 10 | CRVAL4 | Polarization (neg -> Pol, Pos -> Stok | 8D | 8 |
| 11 | CRVAL5 | Time at Exposure start (sec since DAT | 8D | 8 |
| 12 | IF | Subcorrelator | 8D | 8 |
| 13 | TSYS | Tsys | 8D | 8 |
| 14 | OBSFREQ | Center Frequency | 8D | 8 |
| 16 | DOP-USED | Doppler Shift Used | 8D | 8 |
| 17 | DOP-NOW | Correct Doppler Shift during dump (No | 8D | 8 |
| 18 | DOP-TIME | Time since Doppler was set | 8D | 8 |
| 19 | RESTFREQ | Rest freq at band center | 8D | 8 |
| 20 | VELOCITY | Optical Velocity | 8D | 8 |
| 21 | REDSHIFT | Optical Redshift | 8D | 8 |
| 22 | VELDEF | Velocity Reference Frame | 8A | 8 |
| 23 | JD | Julian Day Number at Exposure Start | 8D | 8 |
| 24 | LST | Local Mean Siderial Time at exposure | 8D | 8 |
| 26 | SCAN | Scan Number: YDDDnnnnn | 8D | 8 |
| 27 | OBSMODE | Observing Mode. PSSW is position swi | 8D | 8 |
| 28 | NPHASE | how many scans in a pattern | 8D | 8 |
| 29 | PHASEID | which scan in a pattern | 8D | 8 |
| 30 | GRPNUM | Exposure Number | 8D | 8 |
| 31 | AZIMUTH | Encoder Azimuth on sky (not feed) | 8D | 8 |
| 32 | ZEN_ANG | Encoder Zenith Angle | 8D | 8 |
| 33 | ELEVATIO | Encoder Elevation | 8D | 8 |
| 34 | ALT_ZA | Encoder Zenith Angle of other Carriag | 8D | 8 |
| 35 | POS_TIME | Time when AZ and ZA measured | 8D | 8 |
| 36 | LAGS_IN | Lags Acquired | 8D | 8 |
| 37 | NCHAN | Lags Written | 8D | 8 |
| 38 | CORRMODE | Correlator Mode | 8A | 8 |
| 39 | RFNUM | Receiver Number | 8D | 8 |
| 40 | CALNUM | Cal number | 8D | 8 |
| 41 | FRONTEND | Front end identifier | 8A | 8 |
| 42 | LAG_CONFIG | Correlator setup number | 8D | 8 |
| 43 | ATTN_COR | Correlator attenuator | 8D | 8 |
| 44 | PWR_METER | Power from power meter | 8D | 8 |
| 45 | TOT_POWER | Scaled Power in zero-lag | 8D | 8 |
| 46 | CALOFF_POWER | Power with CALOFF | 8D | 8 |
| 47 | CALON_POWER | Power with CALON | 8D | 8 |
| 48 | CORRLEVS | 3 or 9 level sampling | 8D | 8 |
| 49 | BLANKING | Radar blanking if True | 1L | 1 |
| 50 | DNYQUIST | Double Nyquist sampling if True | 1L | 1 |
| 51 | LBWHYB | LBandWide Hybrid is in (for circular | 1L | 1 |
| 52 | UPDNHYB | 10 GHz Hybrid is in (for circular pol | 1L | 1 |