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Robert C. Byrd Green Bank Telescope

NRAO Green Bank

Joe Brandt, Richard Prestage

January 7, 2014
GBT Software Project Note 7.15

The GBT Antenna Control Unit FITS File Specification

PDF Version


The FITS format structure is presented for the GBT Antenna Control Unit (ACU) scan data files. The scan data FITS files are permanently archived after each observation, and will usually be input to the aips++ filler, which has the task of combining all scan data FITS files into an aips++ Measurement Set. This data may then either be processed further in aips++, or written out in an aips++ supported FITS format (one of which is single dish FITS).

The main content of the ACU FITS file is a binary table containing a stream of the actual (indicated) telescope positions sampled at 10Hz through-out the scan.


8th November 2001
Penultimate definition of FITSVER 1.1; released for general comment (Richard Prestage).
16th November 2001
Final version agreed for implementation of FITSVER 1.1. Added keywords SITESYS and SITETYPE, and modified discussion of SITELONG, SITELAT, SITEELEV. Changed actual values used. Changed description of contents of MAJOR and MINOR if INDICSYS is OTHER. Subsequent changes to the content of this document should increment the document version number (Richard Prestage).
16th October 2002
Added information for initial implementation of beam offsets and multi-feed support. FITSVER revised to 1.3.
24th June 2003
Added OBSC_AZ and OBSC_EL columns. FITSVER revised to 1.4.
9th July 2003
Added SOBSC_AZ, SOBSC_EL, SMNT_AZ, SMNT_EL, SDMJD, OFFSYS, and ORADESYS primary header keys. FITSVER revised to 1.5.
15th December 2003
Added DYN_ENA, SDYN_AZ1, SDYN_AZ2, SDYN_EL, SDYN_FTKYP, to primary header keys. Added DYN_POINT and DYN_FOCUS tables. FITSVER revised to 1.6.
30 Apr 2004
Added notes on beam offset table references. FITSVER revised to 1.7.
28 Feb 2006
Corrected 300ms offset in OBSC_AZ and OBSC_EL columns. FITSVER revised to 1.8.
24 Mar 2006
Added LFC_* and FTRK* primary header keywords. FITSVER revised to 2.9.
17 May 2006
Added WEATHSTA primary header keyword. FITSVER revised to 2.10 (First Linux version.)
1 August 2007
Revised to implement pointing Model 5, revising FITSVER to 2.11. Added additional primary header keywords for new model.
28 September 2007
Revised to correct an error introduced in the FITSVER 2.11 version. The version 2.11 files have an error in the SOBSC_EL keyword and OBSC_EL column. The values omit refraction. The correct values for OBSC_EL may be obtained by adding the values from the REFRACT column.
31 Jan 2008
Revised description of OBSC_AZ and OBSC_EL columns in primary table to include modal behavior. No version revision.
28 March 2008
Revised to indicate changes in manager, no FITS format changes.
14 May 2010
Revised section 1.6 to fix error in sign of equations showing how to apply the beam offsets.
10 Jan 2010
Revised for new Beam specification syntax. FITSVER 14.
7 Jan 2014
Added plate scan keywords PLSCALXT and PLSCALZT. FITSVER 15.

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Joe Brandt 2014-01-07