***** File LBLFORM.TXT                                                        
                                                                              
                                                                              
                          PDS Label 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 (PDS).                                          
                                                                              
     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.LBL).  A short list of this convention by        
Discipline and subnet (or experiment) is given below for PDS labels:          
                                                                              
                                                                              
                                                                              
  PDS Object              FITS  Discipline      Subnet   Extensions           
 (description)         NAXIS =                   Code                         
______________________________________________________________________        
                                                                              
text                       1    Astrometry       ASTR      .lbl               
FITS_LABEL (no data)       0    IR Studies       IRSP      .lbl               
table (filter)             0,2        "          IRFT      .lbl               
table(photometry)          0,2        "          IRPH      .lbl               
table(polarimetry)         0,2        "          IRPOL     .lbl               
spectrum (filter)          2          "          IRFC      .lbl               
spectrum                   2          "          IRSP      .lbl               
image                      2          "          IRIM      .lbl               
FITS_LABEL (no data)       0    Large Scale Phen LSPN      .lbl               
image(browse)              2          "          LSPN      .lbl               
image                      2    Near Nucleus     NNSN      .lbl               
table (broad band)         0,2  Photometry Polar PMAG      .lbl               
table (narrow band)        0,2        "          PFLX      .lbl               
table (polarization)       0,2        "          PPOL      .lbl               
table (Stokes parameters)  0,2        "          PSTOKE    .lbl               
FITS_LABEL (no data)       0    Radio Studies    RSCN      .lbl               
FITS_LABEL (no data)       0          "          RSSL      .lbl               
spectrum                   1          "          RSSL      .lbl               
spectrum (multiple)     1 or 2        "          RSOH      .lbl               
spectrum(multiple)         2          "          RSRDR     .lbl               
image                      2          "          RSCN      .lbl               
image(multiple)            3          "          RSOC      .lbl               
spectrum (visibility)      6          "          RSCN      .lbl               
spectrum (visibility)      6          "          RSOH      .lbl               
spectrum (visibility)      6          "          RSSL      .lbl               
spectrum                   1    Spectroscopy     SPEC      .lbl               
spectral image qube        2          "          SPEC      .lbl               
image (spectrum)           2          "          SPEC      .lbl               
FITS_LABEL (no data)       0    Amateur Studies  AMDR      .lbl               
FITS_LABEL (no data)       0        "            AMPG      .lbl               
FITS_LABEL (no data)       0        "            AMSP      .lbl               
table (magnitude)          0,2      "            AMV       .lbl               
table (radar)              0,2  Meteor Studies   MSNRDR    .lbl               
table (visual)             0,2      "            MSNVIS    .lbl               
______________________________________________________________________        
                                                                              
                                                                              
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                                    
                 .LBL - detached PDS stream format                            
                 .TAB - table data records as ASCII                           
                                                                              
                                                                              
    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. 
                                                                              
                                                                              
                                                                              
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.