***** File SPECFORM.TXT
Spectra Data Descriptions
The International Halley Watch agreed early on in the project that
all data would be submitted from the individual disciplines to the Lead
Center using the FITS format. 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. The
original FITS byte stream could then be recovered by concatenating the
appropriate header and data files. PDS labels were constructed to allow
definition of the data files for the Planetary Data System. For each
data there must be a file indicating the FITS header.
The convention for naming files on the CD-ROM was proposed by the
IHW Lead Center to include a unique data qualifier for the data. A
specific set of rules was established to identify the net and subnet for
each discipline (given by a letter code). A CD-ROM running number relates
the information contained in the various indices to the files containing
the actual data. A short list of this convention for spectra follows:
PDS Object FITS Discipline Letter File Ext
(description) NAXIS = Code
spectrum 2 IR Studies IRSP .dat
spectrum (position-flux) 2 " IRIM .dat
spectrum 1 Radio Studies RSOH .dat
spectrum(multiple) 2 " RSOH .dat
spectrum 1 Spectroscopy SPEC .dat
spectrum 2 " SPEC .dat
Note that the Subnet coding (explained in the Filenaming Conventions)
is one way to distinguish file extension and content.
The file extensions follow suggestions by the Planetary Data System
(SPIDS v1.1) 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
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 thankfully acknowledge the help of M. Martin,
JPL, for assisting the IHW through version 1.1 of the ODL that allows
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) with an embedded CR and LF.
The SPECTRUM class description wereoutlined in v1.1 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 POSITION; the
last case is really a position-flux binary table or image profile.)
Another case is a table from the Infrared Studies Network of ordered
triples of data, in which we interpreted the column of signal/noise
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.