***** 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.