.. _sdfits-reference: **************** GBT SDFITS Files **************** Convention ========== The single-dish FITS (SDFITS) convention is used for observer-facing GBT data. The GBT records raw data to FITS files, and then the SDFITS filler populates SDFITS files with information the observer needs. GBT SDFITS files contain 2 or more Header-Data Units (HDUs). Note that keys sometimes appear to be truncated because they can only have up to 8 letters. HDU 0 (PRIMARY) --------------- .. _primary-sdfits-header: Header ^^^^^^ .. list-table:: :widths: 25 25 50 :header-rows: 1 * - Key - Value - Definition * - DATE - UTC Timestamp - Date and time the file was created * - ORIGIN - "NRAO Green Bank" - Origin of the observation * - TELESCOP - "NRAO_GBT" - The telescope used for the observation * - INSTRUME - "VEGAS" - The backend used for the observation * - GBTMCVER - "sdfits ver#.##" - Version of SDFITS used to make this file (current: 1.22) * - FITSVER - "#.#" - FITS definition version HDU 1 (SINGLE DISH) ------------------- .. _singledish-sdfits-header: Header ^^^^^^ .. list-table:: :widths: 25 25 50 :header-rows: 1 * - Key - Value - Definition * - XTENSION - "BINTABLE" - binary table extension * - BITPIX - 8 - 8-bit bytes * - NAXIS - 2 - 2-dimensional binary table * - NAXIS1 - integer - width of table in bytes * - NAXIS2 - integer - number of rows in table * - PCOUNT - integer - size of special data area * - GCOUNT - 1 - one data group (required keyword) * - TFIELDS - integer - number of fields in each row * - TELESCOP - "NRAO_GBT" - The telescope used for the observation * - PROJID - string - project identifier * - Backend - "VEGAS" - backend device * - SITELONG - -7.983983E+01 - E. longitude of intersection of the az/el axes * - SITELAT - 3.843312E+01 - N. latitude of intersection of the az/el axes * - SITEELEV - 8.245510E+02 - height of the intersection of az/el axes * - EXTNAME - "SINGLE DISH" - The name of this binary table extension Data ^^^^ .. list-table:: :widths: 20 20 20 40 :header-rows: 1 * - Key - Unit - Type - Definition * - OBJECT - - 32A - name of source observed * - BANDWID - Hz - 1D - bandwidth * - DATE-OBS - - 22A - date and time of observation start * - DURATION - s - 1D - total integration duration in seconds * - EXPOSURE - s - 1D - effective int time (excludes blanking) in seconds * - TSYS - K - 1D - system temperature in Kelvin * - DATA - - 131072E - Actual data * - TDIM7 - - 16A - data dimensions of the array * - TUNIT7 - - 6A - * - CTYPE1 - Hz - 8A - first data axis is frequency-like * - CRVAL1 - Hz - 1D - * - CRPIX1 - index - 1D - * - CDELT1 - Hz - 1D - * - CTYPE2 - - 4A - second axis is longitude-like * - CRVAL2 - deg - 1D - * - CTYPE3 - - 4A - third axis is latitude-like * - CRVAL3 - deg - 1D - * - CTYPE4 - - - fourth axis is Stokes * - CRVAL4 - - 1I - * - OBSERVER - - 32A - name of observer(s) * - OBSID - - 32A - observation description * - SCAN - - 1J - scan number * - OBSMODE - - 32A - observing mode * - FRONTEND - - 16A - frontend device * - TCAL - K - 1E - calibration temperature * - VELDEF - - 8A - velocity definition and frame * - VFRAME - m/s - 1D - radial velocity of the reference frame * - RVSYS - m/s - 1D - radial velocity, Vsource - Vtelescope * - OBSFREQ - Hz - 1D - observed center frequency * - LST - s - 1D - LST at midpoint of integration/scan * - AZIMUTH - deg - 1D - azimuth * - ELEVATIO - deg - 1D - elevation * - TAMBIENT - K - 1D - ambient temperature * - PRESSURE - mmHg - 1D - ambient pressure * - HUMIDITY - - 1D - relative humidity * - RESTFREQ - Hz - 1D - rest frequency at band center * - FREQRES - Hz - 1D - frequency resolution * - EQUINOX - - 1D - equinox of selected coordinate reference frame * - RADESYS - - 8A - Equatorial coordinate system name * - TRGTLONG - deg - 1D - target longitude in coord. ref. frame * - TRGTLAT - deg - 1D - target latitude in coord. ref. frame * - SAMPLER - - 12A - sampler description (e.g., "A1" or "A1xA3") * - FEED - - 1I - (signal) feed number * - SRFEED - - 1I - reference feed number * - FEEDXOFF - deg - 1D - feed XEL offset * - FEEDEOFF - deg - 1D - feed EL offset * - SUBREF_STATE - - 1I - subreflector state (1,0,-1) - 0=moving * - SIDEBAND - - 1A - resulting sideband ('U'pper or 'L'ower) * - PROCSEQN - - 1I - scan sequence number * - PROCSIZE - - 1I - number of scans in procedure * - PROCSCAN - - 16A - scan's role in the procedure * - PROCTYPE - - 16A - type of the procedure * - LASTON - - 1J - last 'on' for position switching * - LASTOFF - - 1J - last 'off' for position switching * - TIMESTAMP - UTC - 22A - date and time of scan start * - QD_XEL - deg - 1D - QuadrantDetector cross-elevation offset * - QD_EL - deg - 1D - QuadrantDetector elevation offset * - QD_BAD - - 1I - QuadrantDetector flag: 0=good,1=bad * - QD_METHOD - - 1A - Quad. Det. method A,B,C. Blank indicates none. * - VELOCITY - m/s - 1D - line velocity in rest frame * - ZEROCHAN - - 1E - zero channel * - DOPFREQ - Hz - 1D - Doppler tracked frequency * - ADCSAMPF - - 1D - VEGAS ADC sampler frequency * - VSPDELT - - 1D - channel increment between adjacent VEGAS spurs * - VSPRVAL - - 1D - VEGAS spur number at VSPRPIX * - VSPRPIX - - 1D - channel number of VEGAS spur VSPRVAL * - SIG - - 1A - signal is true, reference is false * - CAL - - 1A - cal ON is true, cal OFF is false * - CALTYPE - - 8A - LOW or HIGH, may eventually be other types * - TWARM - K - 1E - 4mm RX ambient load temp (K) * - TCOLD - K - 1E - 4mm RX cold load temp (K) * - CALPOSITION - - 16A - 4mm RX table position * - IFNUM - - 1I - Spectral window (IF) number * - PLNUM - - 1I - Polarization number * - FDNUM - - 1I - Feed number Index Files =========== .. list-table:: Header :widths: 25 25 50 :header-rows: 1 * - Key - Value - Definition * - created - Day Month DD HH:MM:SS YYYY - Date file was created * - last_modified - Day Month DD HH:MM:SS YYYY - Date file was last modified * - version - - * - observer - - * - backend - - * - tcal_rx_table - - * - sprotect - - * - created_by - "index_writer" - Method that created this file .. list-table:: Rows :widths: 25 25 50 :header-rows: 1 * - Key - Value - Definition * - INDEX - - * - PROJECT - - * - FILE EXT - - * - ROW - - * - SOURCE - - * - PROCEDURE - - * - OBSID - - * - E2ESC - - * - PROCS - - * - SCAN - - * - POL - - * - PLNUM - - * - IFNUM - - * - FEED - - * - FDNUM - - * - INT - - * - NUMCHN - - * - SIG - - * - CAL - - * - SAMPLER - - * - AZIMUTH - - * - ELEVATION - - * - LONGITUDE - - * - LATITUDE - - * - TRGTLONG - - * - TRGTLAT - - * - SUB - - * - LST - - * - CENTFREQ - - * - RESTFREQ - - * - VELOCITY - - * - FREQINT - - * - FREQRES - - * - DATEOBS - - * - TIMESTAMP - - * - BANDWIDTH - - * - EXPOSURE - - * - TSYS - - * - NSAVE - - * - PROCSCAN - - * - PROCTYPE - - * - WCALPOS - - Flag Files ========== Flag files indicate the data that should be ignored. For example, these flags can include the locations of VEGAS spurs. `GBTIDL` sometimes auto-masks data that is flagged in these files immediately upon start. .. list-table:: Header :widths: 25 25 50 :header-rows: 1 * - Key - Value - Definition * - created - Day Month DD HH:MM:SS YYYY - Date file was created * - version - 1.0 - Version of ? * - created_by - sdfits - Created by the SDFITS filler .. list-table:: Flags :widths: 25 25 50 :header-rows: 1 * - Key - Value - Definition * - RECNUM - integer or "*" - * - SCAN - integer or "*" - Scan number * - INTNUM - integer or "*" - Integration number * - PLNUM - integer or "*" - Polarization number * - IFNUM - integer or "*" - Spectral window (IF) number * - FDNUM - integer or "*" - Feed number * - BCHAN - list of integers - * - ECHAN - list of integers - * - IDSTRING - "VEGAS_SPUR" - Type of flag Other Resources =============== The full SDFITS documentation for GBO can be found on `the GBT SDFITS Project Wiki `_. However, this page is out of date and requires a login to view.