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Primary HDU keywords

The holography backend FITS keywords for the primary HDU conforms to the definition for common FITS headers as described in GBT Software Project Note 4.0 ``Device and Log FITS Files for the GBT.''

An example primary header is shown below:

SIMPLE  =                    T / file does conform to FITS standard
BITPIX  =                    8 / number of bits per data pixel
NAXIS   =                    0 / number of data axes
EXTEND  =                    T / FITS dataset may contain extensions
COMMENT   FITS (Flexible Image Transport System) format is defined in 'Astronomy
COMMENT   and Astrophysics', volume 376, page 359; bibcode: 2001A&A...376..359H
ORIGIN  = 'NRAO Green Bank'    /
INSTRUME= 'Holography'         / device or program of origin
GBTMCVER= 'integration'        / telescope control software release
FITSVER = '2.2     '           / FITS definition version for this device
DATEBLD = 'DATEBLD  goes  here' / time program was linked
SIMULATE=                    1 / Is the instrument in simulate mode?
DATE-OBS= '2008-03-19T00:00:04' / Manager parameter startTime
TIMESYS = 'UTC     '           / time scale specification for DATE-OBS
TELESCOP= 'NRAO_GBT'           / Green Bank Telescope (Robert C. Byrd 100m)
OBJECT  = '1800+7828'          / Manager parameter source
PROJID  = 'TREG    '           / Manager parameter projectId
OBSID   = 'unit_test'          / Manager parameter scanId
SCAN    =                   34 / Manager parameter scanNumber
UTDATE  =                54544 / MJD of start time
UTCSTART=   3.600000000000E+00 / Start time
CYCLETIM=   1.000000000000E-01 / Switching period in seconds
CYCLES  =                    1 / Switching periods per Integration
DURATION=   1.000000000000E-01 / Integration time
TESTATTN=                    5 / Test input attenuation db's (0-31)
REFATTEN=                    2 / Reference input attenuation db's (0-31)
END

The primary header keywords for the holography backend FITS files are as follows:

The first four items are mandatory FITS keywords.

ORIGIN is a reserved FITS standard keyword.

INSTRUME is the FITS standard keyword used to specify the ``instrument'' responsible for producing the data in the file. This will be set to the string Holography for all holography FITS files.

GBTMCVER, FITSVER, DATEBLD, and SIMULATE are GBT-specific keywords.

GBTMCVER refers to the version of the M&C system in use at the time the file was created.

FITSVER refers to the version of the GBT FITS definition the file conforms to. The leading number refers to the global definition version (i.e. this document), while the trailing number refers to a revision specific to this specific type of FITS file. For example, a value of 2.5 in a Spectrometer FITS file would imply the fifth revision of the Spectrometer FITS file definition conforming to the second revision of the global GBT FITS standards.

DATEBLD is generated automatically via the Unix command ``date -u +whenever the program which actually writes the FITS file is linked.

SIMULATE specifies whether the program was running in simulation mode when the file was written.

DATE-OBS is the FITS standard keyword to specify the date and time of the start of an observation. As recommended in the standard, the UTC time scale is explicitly specified using the TIMESYS keyword. This time in GBT Device files represents the nominal scheduled time and is therefore represented only to the nearest second.

TELESCOP is a reserved FITS standard keyword.

OBJECT is the FITS standard, and PROJID, OBSID and SCAN pre-existing FITS keywords used to define these quantities, and so are used here. The corresponding GBT M&C base manager parameters are indicated in the comments.

The following are additional header keywords added for the holography manager:

UTDATE is the modified Julian Day (MJD) of the start of the observation.

UTCSTART is the number of seconds since midnight UTC of the start of the observation.

CYCLETIM is the duration of the sub-integration time, in seconds.

CYCLES is the integer number of sub-integrations accumulated before passing the data onto the manager. Therefore the typical integration time is CYCLETIM*CYCLES in seconds.

DURATION is the length in seconds of the each integration time. This should be equal to the cycletime times the number of cycles per integration.

TESTATTN is the amount of input attenuation of the main (i.e. GBT) signal input.

REFATTEN is the amount of input attenuation in db of the reference signal input.


next up previous
Next: Binary Image Up: gbtHoloFits Previous: Background
Bob Garwood 2011-07-25