***** File HALGUIDE.TXT                                                       
                                                                              
                                                                              
                        Comet Halley Archive                                  
              User's Guide to IHW CD-ROM Volumes 19-23                        
                                                                              
                                                                              
                                                                              
                               Contents                                       
                                                                              
                                                                              
1. Background and Scope of Compact Disc                                       
2. Accessing the Disc                                                         
3. Data Products on these Discs                                               
4. Supplemental Directories                                                   
5. Filenaming Conventions                                                     
6. References                                                                 
                                                                              
                                                                              
                                                                              
1. BACKGROUND AND SCOPE OF COMPACT DISC                                       
                                                                              
     This compact disc (CD-ROM), and the series of discs of which it is a     
part, contains observations of comet P/Halley obtained during the 1985-1986   
apparition.  The resulting digital archive is the main product of the         
International Halley Watch (IHW), which was formed in 1981 to mount an        
international campaign to observe the comet over a long baseline in time.  The
collection of remote (mostly ground-based) data archived here spans a wide    
wavelength range and is augmented (on other discs) by measurements made in    
situ by the spacecraft which encountered the comet in 1986 March.  The remote 
observations are associated with nine IHW Disciplines:  Astrometry, Infrared  
Studies, Large-Scale Phenomena (L-SP), Meteor Studies, Near-Nucleus Studies,  
Photometry and Polarimetry, Radio Studies, Spectroscopy and Spectrophotometry,
and Amateur Observations.                                                     
                                                                              
     The complete IHW digital archive is comprised of four subsets of CD-ROMs 
containing:                                                                   
                                                                              
  o Compressed Halley images from the L-SP Discipline (Volumes 1-18),         
  o Halley data from all IHW Disciplines (Vols. 19-23),                       
  o IHW "Trial Run" data of comets P/Crommelin & P/Giacobini-Zinner (Vol. 24),
  o Halley spacecraft data (Vols. 25-26)                                      
                                                                              
The total collection for Halley's Comet contains more than 37,000 independent 
files and 15 Gbytes of data.  This document is intended as a guide to Volumes 
19-23.  [CDTREE.TXT and DATATREE.TXT are useful files within the DOCUMENT     
directory to which the archive user may wish to refer to visualize the        
structure and content of these discs as he or she reads this document.]       
                                                                              
                                                                              
2. ACCESSING THE DISC                                                         
                                                                              
     These discs have been manufactured following the normal specifications   
for Compact Disc Read Only Memory (CD-ROM) as well as the logical structure   
outlined by the International Standards Organization (ISO) in the No. 9660    
document.  A basic system requirement demands that the CD-ROM reader and      
software driver support this standard.  At this writing (July 1990), primary  
access to the disc will be using IBM-PC or compatible computers.  However,    
software support from vendors for the Apple MacIntosh II and some workstations
(SUN, MicroVAX) is now available.                                             
                                                                              
     If you are using a PC style machine, the reader that you bought should   
include the appropriate hardware (a PC-bus or SCSI controller board and cable)
and software to address your device.  Software packages should include a      
device driver for your machine and extensions to DOS that allow the reader to 
"look" like another random access disk drive; the de facto standard here is   
the Microsoft Extensions (MSCDEX 2.0 or higher).  Install the specific device 
driver software as directed by the documentation accompanying the hardware.   
Usually, this will involve specifying the device driver in a DEVICE= line in  
the CONFIG.SYS file and invoking the extensions package from your AUTOEXEC.BAT
file.  This will automatically configure the CD-ROM reader when the computer  
is booted.                                                                    
                                                                              
     Remember that the CD-ROM reader is assigned a drive name which you have  
either chosen with the appropriate command line switch (/L:H assigns the CD-  
ROM reader to drive H:) or allowed to default to the next available device    
letter in your system.  Typical PC configurations will have two floppies (A:  
and B:), and a hard disk (C:).  Put your drive at some letter higher than     
that.  Remember that many DOS commands work on the CD-ROM but that it is a    
read-only medium.  Some of the useful DOS functions are:                      
                                                                              
        DIR   - directory listing                                             
        CHDIR - change directory (also CD)                                    
        TYPE  - list the contents of a file on the screen; useful             
                for normal text with <carriage return>, <line feed>           
                delimiters                                                    
        COPY  - copy file(s) to another device                                
        PRINT - print file on hard copy device                                
                                                                              
     Notice that commands such as DEL and MKDIR are not available since the   
CD-ROM is a read-only medium.  Furthermore, some compact disc software        
packages will invoke screen plots that may depend on the DOS program          
GRAPHICS.COM.  In this case, execute it in your AUTOEXEC.BAT file or before   
you run the software package.                                                 
                                                                              
     The IHW CD-ROMs have been designed to allow maximum access to the data   
using existing software developed within NASA, as well as user-supplied       
programs.  In particular, each data file was originally supplied in the FITS  
format, and also has a detached PDS label to describe the data structure.     
Furthermore, the normal FITS files have had the headers placed in files (with 
extension .HDR) separate from the data (.DAT, .IBG, .IMG, .TAB).  The         
headers have been separated to allow unrestricted access to the data by       
non-FITS programs.  The sizes of all header and data files have been preserved
as integer multiples of 2880 bytes (required by FITS) in order to facilitate  
the reconstruction of the original FITS bytestream by concatenating the data  
file with the appropriate header file.                                        
                                                                              
                                                                              
                                                                              
3. DATA PRODUCTS ON THESE DISCS                                               
                                                                              
     The majority of the ground-based data is located in directories whose    
organization is chronological.  The directory names themselves are based on   
one or more parameters of time, the complete set being Year, Month, Day, and  
UT Hour; the time referred to reflects the approximate beginning of the       
directory's data contents (filenaming conventions are discussed in Section 5).
We have restricted directories to a reasonable number of files while allowing 
enough information for useful browsing; 256 was adopted as the desired maximum
number, which includes datafiles, headers, and PDS labels. Given the large    
variation of the temporal density of IHW observations throughout the          
apparition, the "reasonable N" < 256 criterion resulted in directories        
widely divergent in duration.  For example, all observations for 1983 were    
deposited in one directory, whereas for 1986 April there were many days which 
required directories only 3 hours wide (sample directory name:                
Y1986\M04\D10\H18).  The smallest hourly subdivision is, in fact, 3 hours     
(03,06,09,....hours UT).  No subdirectory was created for days on which data  
were not submitted.  Across the entire set of ground-based data discs (Volumes
19-23), the typical file count in a directory is 50, and the average byte     
count is 1.0 Mbyte.                                                           
                                                                              
     Not all the IHW remote data on these discs (Volumes 19-23) reside        
on one directory level, although the majority of them--those from six of the  
Disciplines--do.  Those six Disciplines are:                                  
                                                                              
       o Infrared Studies                                                     
       o Large-Scale Phenomena (browse images and dataless headers)           
       o Near-Nucleus Studies                                                 
       o Photometry and Polarimetry                                           
       o Radio Studies                                                        
       o Spectroscopy and Spectrophotometry                                   
                                                                              
The approach has been to include Halley datafiles (and headers and labels)    
from these Disciplines in the appropriate chronological directory (e.g.,      
Y1986\M04\D10\H18).                                                           
                                                                              
     The full-resolution images from the Large-Scale Phenomena (L-SP)         
Discipline have been deposited on a different series of IHW discs--Volumes    
1-18--in compressed form.  Details of the compression algorithm and the       
accompanying FITS proposal are in the file FITSCOMP.TXT in the DOCUMENT       
directory of those discs.  Descriptions of the discs' full contents and       
structure, as well as the rationale for performing data compression, are to be
found in the documentation on Volumes 1-18 and in the LS_PHEN.APX file in the 
\DOCUMENT\APPENDIX directory of this disc.  A useful file which shows the time
range of each L-SP compressed image disc is SUMINFO.TXT, located in the       
DOCUMENT directory of Volume 18.  Inclusion of subsampled, "browse" versions  
of the same L-SP images on these discs (Vols. 19-23) was thought to be        
important for inter-disciplinary comparisons between all types of IHW data.   
These images are restricted to a maximum of 256 one-byte pixels on a side, and
preserve the original sampling geometry.  They may be especially important for
"quick look" assessments of the full-resolution images, which are relatively  
time-consuming to decompress.                                                 
                                                                              
     The data for three IHW Disciplines--Astrometry, Amateur Observations, and
Meteor Studies--are stored in different locations on these discs (Volumes     
19-23), as follows.  Astrometry and Amateur Observations are located one      
directory level below the "main data level" discussed above (sample path for  
Astrometry is: Y1985\M12\D12\H18\ASTROM), whereas the data for the Meteor     
Studies Discipline are contained in 59 files in a dedicated directory on      
Volume 23.  It is to be noted that on occasion, a high density of either      
Astrometry or Amateur files drove the temporal widths of the "main data level"
since the N(max)=256 criterion applied to the lowel levels (Astrometry and    
Amateur) as well.                                                             
                                                                              
     Some Disciplines submitted supplemental data which include filter tables,
non-comet images, flat fields, and laboratory spectra.  These files are stored
in the CALIB directory of Volume 23, and the numeric part of their filename   
begins at a higher number (4001) than does the actual Halley data (0001).  The
reader should consult Section 5 for more details on filenaming.               
                                                                              
     A large number of scientists contributed to this archive project. They   
are listed in the \DOCUMENT\OBSERVER directory of the these discs, by the IHW 
Discipline to which they contributed data. The contributing observatories,    
with their IHW system codes, are listed in the file OBSCODES.TXT (directory   
\DOCUMENT\OBSVTRY of Volume 23).  Individual observers and their various      
instruments are, of course, also identified in the FITS header that           
accompanies the data.                                                         
                                                                              
                                                                              
                                                                              
4. SUPPLEMENTAL DIRECTORIES                                                   
                                                                              
     The volume and directory structure of this disc conform to the Level-1   
standard specified by the ISO.  This format is widely accepted and used on a  
variety of machines.  The AAREADME.TXT file in the root directory introduces  
the user to the full extent of the archive and the contents of the individual 
subdirectories.                                                               
                                                                              
     There are four directories (DOCUMENT, EPHEM, INDEX and SOFTWARE) on this 
disc that contain supplementary files.  The DOCUMENT directory contains text  
files that give the background to this CD-ROM project, present a general guide
to its use, and detail experience with previous CD-ROM products, including a  
test disc of comet Giacobini-Zinner data (also archived by the IHW) and two   
test discs of Halley data (refer to VOLINFO.TXT).  A discussion of the FITS   
and PDS formats and the metadata used specifically for the Halley data is     
located in the files FITS_IHW.TXT and PDS_IHW.TXT.  This file (HALGUIDE.TXT)  
and IMAGUIDE.TXT on Volumes 1-18 are meant to serve as general overviews of   
the discs and their contents.  Documents in the APPENDIX subdirectory, written
by the IHW Discipline Specialists, contain information on data collection,    
subsequent processing steps, and archiving techniques, at the Discipline      
level.                                                                        
                                                                              
     In the INDEX directory, tables of useful information have been indexed in
various forms in order to allow automated searching of the data. The QUIK.IDX 
index contains a selected set of mandatory FITS keywords from all Disciplines.
On each of Volumes 19-23, QUIK.IDX includes only the observations on that     
disc.  Volume 23 has an additional, "summary quick index", QUIK_SUM.IDX, which
includes all observations contained in Volumes 19-23; the last field in       
QUIK_SUM.IDX includes the Volume number.  A set of tables in the subdirectory 
NETABLES contains the metadata/data from the proposed printed archive,        
organized by network and subnetwork and chronologically ordered in each index.
In this subdirectory, also, are more complete indices of FITS keywords for    
five of the IHW Disciplines.  The filenames (Disciplines) are:  NETAMATV.IDX  
(Amateur Observations), NETLARGE.IDX (Large-Scale Phenomena), NETMETR.IDX and 
NETMETV.IDX (Meteor Studies), NETRADIO.IDX (Radio Science), and NETSPECT.IDX  
(Spectroscopy and Spectrophotometry).  We constructed a separate index called 
PATHTABL.IDX to specify the full path to each datafile; these are organized by
disc, and a summary version is contained on Volume 23.  We attempted to make  
all index tables transportable to relational DBMS by delimiting the tables and
providing structure (.STR) and dBASE-compatible (.DBF) files. Further         
information about IHW indices is contained in the file INDXINFO.TXT.          
                                                                              
     The SOFTWARE directory contains source code and executables for display  
of imaging and spectral data, interpolation of ephemeris tables, reading of   
FITS tables, and manipulation of metadata.  To be specific, IMDISP.EXE        
contains various utilities for manipulating visual data on image display      
devices; IMDISP was originally developed by the Planetary Data System (PDS) at
the Jet Propulsion Laboratory (JPL), and has been augmented and improved by   
them and by outside users.  The interpolation software is meant to be used on 
the EPHEM.TAB file in the EPHEM directory; the algorithm uses values of       
ephemeris data for 7 consecutive integral days to perform the interpolation.  
The Fortran source code is called OBSNTERP.FOR, which we have compiled and    
linked on VAX and PC computers; the resulting executables for VAX/VMS and     
MS-DOS operating systems are VAXNTERP.EXE and PCNTERP.EXE, respectively.  Also
provided on these discs is a "FITS Table Browser" called FTB.EXE, which was   
developed by the Astronomical Data Center (ADC) of the National Space Science 
Data Center (NSSDC).  Several other support programs for manipulating the     
metadata--FITSUTIL, FITSXTND, FITS2TXT, and TXT2FITS--are also provided.  The 
archive user should take note of the fact that on the L-SP compressed image   
discs (Volumes 1-18), additional source code and executables exist for        
compression and decompression of the large image files contained on those     
discs.                                                                        
                                                                              
                                                                              
                                                                              
5. FILENAMING CONVENTIONS                                                     
                                                                              
     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 organized by Discipline      
and listing subnetwork names and letter codes is given below:                 
                                                                              
                                                                              
  Discipline            Number    Subnet (Exp)   Subnet Code                  
______________________________________________________________________        
                                                                              
 Astrometry                1           none         ASTR                      
 Infrared Studies          2       Photometry       IRPH                      
                                   Polarimetry      IRPOL                     
                                   Spectroscopy     IRSP                      
                                   Image            IRIM                      
                                   Filter Table     IRFT                      
                                   Filter Curve     IRFC                      
 Large-Scale Phenomena     3          none          LSPN                      
 Near Nucleus Studies      4          none          NNSN                      
 Photometry Polarimetry    5       Broad Band Mag   PMAG                      
                                   Narrow Band Flux PFLX                      
                                   Polarimetry      PPOL                      
                                   Stokes           PSTOKE                    
 Radio Science             6       Continuum        RSCN                      
                                   Occultation      RSOC                      
                                   OH               RSOH                      
                                   Radar            RSRDR                     
                                   Spectral Line    RSSL                      
 Spectroscopy Spectrophot  7           none         SPEC                      
 Amateur Observations      8       Drawing          AMDR                      
                                   Photography      AMPG                      
                                   Spectroscopy     AMSP                      
                                   Visual Magnitude AMV                       
 Meteor Studies            9       Radar            MSNRDR                    
                                   Visual Estimates MSNVIS                    
______________________________________________________________________        
                                                                              
                                                                              
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 International Halley Watch agreed early in the project that all data 
would be submitted by the individual Disciplines to the JPL 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.  The tabular data, even though presented as valid FITS data       
records, are really just ASCII byte strings that can be exported to many      
machines.  In addition, detached PDS labels were constructed to allow parallel
definition of the data files for the Planetary Data System. (We thankfully    
acknowledge the help of M. Martin, PDS, for assisting the IHW through version 
2.0 of the Object Description Language to describe the SPECTRUM object.)      
                                                                              
     The file extensions follow suggestions by the Planetary Data System      
(SPIDS v1.1) for tabular and image data, and are 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                           
                                                                              
                                                                              
     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.  
                                                                              
     Inclusion of the PDS labels allows use of CD-ROM imaging software already
available from JPL.  The PDS labels are text files, with lines terminated by  
the <CR><LF> characters. The total size of the files is maintained in the     
required SFDU_LABEL.                                                          
                                                                              
                                                                              
                                                                              
6. REFERENCES                                                                 
                                                                              
Martin, T., Martin, M., Braun, M., Johnson, T., Davis, R., and Mehlman, R.,   
SPIDS: Standards for the Preparation and Interchange of Data Sets, JPL        
D-4683: October 3, 1988.                                                      
                                                                              
"Information Processing -- Volume and File Structure of CD-ROM for            
Information Interchange", Reference Number ISO 9660: 1988(E), Developed in    
coordination with the National Information Standards Organization, National   
Bureau of Standards, Administration 101, Library E-106, Gaithersburg, MD.