***** File SPECFORM.TXT Spectra 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. 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. A short list of this convention for spectra follows: PDS Object FITS Discipline Subnet Extensions (description) NAXIS = Code ______________________________________________________________________ spectrum (filter) 2 IR Studies IRFC .dat spectrum 2 " IRSP .dat spectrum 1 Radio Studies RSSL .dat spectrum (multiple) 1 or 2 " RSOH .dat spectrum (multiple) 2 " RSRDR .dat spectrum (visibility) 6 " RSCN .dat spectrum (visibility) 6 " RSOH .dat spectrum (visibility) 6 " RSSL .dat spectrum 1 Spectroscopy SPEC .dat spectral image qube 2 " SPEC .dat ______________________________________________________________________ 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 IRSP 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 or non-table data .HDR - FITS header records .LBL - detached PDS stream format These PDS labels are metadata (as headers describing data submitted to the archive). There has been no effort to duplicate the documentation contained in the full FITS headers because the PDS and FITS headers for a given data file differ only in the filename extension. Instead we have attempted to use the power of the PDS label syntax to fully describe the data structures and thus gain access to software by that group. Standards for the Preparation and Interchange of Data Sets, Martin, T. Z., et al, Document D-4683, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA document version 1.1 was the primary reference to the Object Description Language (ODL) necessary to create the PDS labels. (We acknowledge R. Borgen and M. Martin, PDS-CN, JPL, for assisting the IHW through version 2.0 of the ODL implementation for SPECTRUM.) The basic PDS descriptors such as SFDU_LABEL, RECORD_TYPE, RECORD_BYTES, and FILE_RECORDS are explained in the SPIDS document. The RECORD_TYPE for all data files is FIXED_LENGTH. The PDS labels have been formed as fixed length (78 byte) plus an embedded CR and LF. The SPECTRUM class description was refined in v2.0 by working closely with the PDS group to ensure definition of data groups that included both uniformly spaced data (as a single array) as well as ordered groups of observations. From guidelines for dealing with the SPECTRUM data structure, we consider the spectra as tabular data (COLUMN, NAME, DATA_TYPE, START_BYTE, BYTES) which are binary. The independent variable (e.g., WAVELENGTH) is described by the keywords SAMPLING_PARAMETER_NAME, MINIMUM_SAMPLING_PARAMETER, SAMPLING_PARAMETER _INTERVAL, and SAMPLING_PARAMETER_UNIT. (There are special cases for Radio or IR data using Doppler VELOCITY, FREQUENCY, or FREQUENCY_OFFSET.) Another case is a table from the Infrared Studies Network of ordered sets of data, in which we interpreted the column of signal/noise or ratios as an associated ERROR. A NOTE about this nonstandard use is included in the labels for the appropriate datasets. We have also attempted to use the NOTE keyword to identify the contributing IHW discipline, subnet, and generic comments about the data. As in the situation for multiple images, we have subclasses for the spectra indicated by a modifier, e.g., LHC_POLARIZATION_SPECTRUM. A special effort was made to describe 2-dimensional spectra by working with the PDS to establish a SPECTRAL_IMAGE_QUBE object. The data are reduced measurements that have the slit oriented either along the tail or perpendicular to the tail of the comet. To capture the positional information, a vectorial notation was adopted for the SPECTRAL_IMAGE_QUBE that could allow for such observational selection. In cases where the derived units were non-standard, a text DESCRIPTION is embedded in the label. There was one case of a binary table that was used to describe the UVFITS data. A hybrid description (VISIBILITY_SPECTRUM), incorporating both the ordered sets and uniformly spaced data, describes this intermediate processing step in data reduction; the integer values are Complex numbers, not currently supported under PDS. 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.