📚 HDRFORM.TXT
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106 lines***** File HDRFORM.TXT
FITS Header Descriptions
The International Halley Watch agreed early in the project that all data
would be submitted from the individual Disciplines to the Lead Center using
the FITS format (Wells et al., 1981). When the decision was made to
distribute this information on CD-ROM, it was determined that the data had to
have even broader accessibility. For this reason the original FITS files,
with contiguous headers and data, were split into separate files
distinguishable by their filename extensions (.HDR for headers). The file
sizes were preserved as multiples of 2880 bytes, allowing the original FITS
byte stream to be recovered by concatenating the appropriate header and
datafile. PDS labels were constructed to allow definition of the datafiles
for the Planetary Data System. For each datafile there must always be an
associated FITS header.
The convention for naming files on the IHW CD-ROMs was proposed by the
Lead Center and NASA/Goddard Space Flight Center (GSFC) personnel to include a
unique data qualifier for the data. Specifically, a set of subnet codes was
established to enable identification of the IHW Discipline/subdiscipline from
the filename itself. A CD-ROM running number and file extension complete the
filename (example: LSPN0059.HDR). A short list of this convention by
Discipline and subnet (or experiment) is given below (for headers only):
PDS Object FITS Discipline Subnet File Ext
(description) NAXIS = Code
______________________________________________________________________
text 1 Astrometry ASTR .hdr
fits_label (no data) 0 IR Stduies IRSP .hdr
table (filter) 0,2 IR " IRFT .hdr
table(photometry) 0,2 IR " IRPH .hdr
table(polarimetry) 0,2 IR " IRPOL .hdr
spectrum(filter) 2 IR " IRFC .hdr
spectrum 2 IR " IRSP .hdr
image 2 IR " IRIM .hdr
fits_label (no data) 0 Large Scale Phen LSPN .hdr
image(browse) 2 Large " LSPN .hdr
image 2 Near Nucleus NNSN .hdr
table (narrow band) 0,2 Photometry Polar PFLX .hdr
table (broad band) 0,2 " PMAG .hdr
table (polarization) 0,2 " PPOL .hdr
table (Stokes parameters) 0,2 " PSTOKE .hdr
fits_label (no data) 0 Radio Studies RSCN .hdr
fits_label (no data) 0 " RSSL .hdr
spectrum 1 " RSSL .hdr
spectrum(multiple) 1 or 2 " RSOH .hdr
spectrum(multiple) 2 " RSRDR .hdr
image 2 " RSCN .hdr
image(multiple) 3 " RSOC .hdr
spectrum (visibility) 6 " RSCN .hdr
spectrum (visibility) 6 " RSOH .hdr
spectrum (visibility) 6 " RSSL .hdr
spectrum 1 Spectroscopy SPEC .hdr
spectral image qube 2 " SPEC .hdr
image 2 " SPEC .hdr
fits_label (no data) 0 Amateur AMDR .hdr
fits_label (no data) 0 " AMPG .hdr
fits_label (no data) 0 " AMSP .hdr
table (magnitude) 0,2 " AMV .hdr
table (radar) 0,2 Meteor MSNRDR .hdr
table (visual) 0,2 " MSNVIS .hdr
______________________________________________________________________
A table linking the subnet codes above and the subdiscipline names is given in
Section 5 ('Filenaming Conventions') of the file HALGUIDE.TXT. Concerning the
numeric portion of filenames, calibration files for IRIM, IRSP, LSPN, and SPEC
begin at 4001, whereas the Halley data themselves for all disciplines and
subdisciplines start at 0001.
The file extensions follow suggestions by the Planetary Data System
(SPIDS v1.1; Martin et al., 1988) for tabular and image data. In addition,
for IHW FITS, the original headers and data were split into separate files,
with header filename extensions as listed below.
.HDR - FITS header records
We have conformed with the PDS definition of a specific keyword to
indicate the presence of a FITS header (the keyword TYPE = FITS) when the
"data" object is a foreign label (FITS_LABEL). In FITS, if NAXIS=0, then no
data records need follow, as in the case of an upper limit. The "dataless"
headers can be recognized by the NAXIS value or the IHW keyword DAT-FORM =
NODATA in the FITS HEADER. The PDS label (with same filename but differing
extension) points at the HEADER file as its data object. As shown in the
above table, the "dataless" header can occur for different types of data:
images (LSPNNNNN or IRIMNNNN), spectra which can be ordered groups (IRSPNNNN)
or standard (RSSLNNNN), and existing but not archived data as for AMDRNNNN,
AMPGNNNN, AMSPNNNN.
REFERENCES
Martin, T.Z., Martin, M.D., Davis, R.L., Mehlman, R., Braun, M., Johnson
M.: October 3, 1988, Standards for the Preparation and Interchange of
Data Sets, Version 1.1, JPL D-4683.
Wells, D.C., Greisen, E.W., and Harten, R.H.: 1981, Astron. Astrophys.
Suppl. Ser. 44, 363.