***** File FITSFORM.TXT FITS Data 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. In cases where no digital data had been supplied the .HDR file carries information about upper limits, values reported by observers, references gleaned from the literature, or the characteristics of data in analog form. The table below identifies these "dataless" files and provides the correspondence between file extension and types of data so that a concatenated file (.FIT) can be reconstructed. 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.IBG). A short list of this convention by Discipline and subnet (or experiment) is given below: PDS Object FITS Discipline Subnet File Extensions (description) NAXIS = Code (.HDR+.EXT=.FIT) _________________________________________________________________________ text 1 Astrometry ASTR .hdr .dat fits_label (no data) 0 IR Studies IRSP .hdr table (filter) 0,2 " IRFT .hdr .tab table (photometry) 0,2 " IRPH .hdr .tab table (polarimetry) 0,2 " IRPOL .hdr .tab spectrum (filter) 2 " IRFC .hdr .dat spectrum 2 " IRSP .hdr .dat image 2 " IRIM .hdr .img fits_label (no data) 0 Large Scale Phen LSPN .hdr image(browse) 2 " LSPN .hdr .ibg image 2 Near Nucleus NNSN .hdr .img table (narrow band) 0,2 Photometry Polar PFLX .hdr .tab table (broad band) 0,2 " PMAG .hdr .tab table (polarization) 0,2 " PPOL .hdr .tab table (Stokes parameters) 0,2 " PSTOKE .hdr .tab fits_label (no data) 0 Radio Studies RSCN .hdr fits_label (no data) 0 " RSSL .hdr spectrum 1 " RSSL .hdr .dat spectrum (multiple) 1 or 2 " RSOH .hdr .dat spectrum (multiple) 2 " RSRDR .hdr .dat image 2 " RSCN .hdr .img image(multiple) 3 " RSOC .hdr .img spectrum (visibility) 6 " RSCN .hdr .dat spectrum (visibility) 6 " RSOH .hdr .dat spectrum (visibility) 6 " RSSL .hdr .dat spectrum 1 Spectroscopy SPEC .hdr .dat spectral image qube 2 " SPEC .hdr .dat image (spectrum) 2 " SPEC .hdr .img fits_label (no data) 0 Amateur Studies AMDR .hdr fits_label (no data) 0 " AMPG .hdr fits_label (no data) 0 " AMSP .hdr table (magnitude) 0,2 " AMV .hdr .tab table (radar) 0,2 Meteor Studies MSNRDR .hdr .tab table (visual) 0,2 " MSNVIS .hdr .tab _________________________________________________________________________ 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 filename extensions as listed below. .DAT - other non-image and non-tabular data .FIT - original FITS file .HDR - FITS header records .IBG - data records for subsampled browse image .IMG - image data records .TAB - table data records as ASCII The five PDS objects in this archive are FITS_LABEL (header), IMAGE, TABLE, TEXT, and SPECTRUM; a label occurs for each datafile. Our aim was to construct a basic PDS label for each data file on the CD-ROM. Files that remain in the original FITS form do not have a PDS label; these can occur as DOCUMENT files and datafiles for Comet Crommelin and Comet Giacobini-Zinner. 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.