RADIO SCIENCE NETWORK                            
                                                                              
                                                                              
1. INTRODUCTION                                                               
                                                                              
     Radio Astronomy is a developing new technique for the study of comets.   
In some areas, such as observations of the OH radical via its 18 cm           
transitions, the observational procedures and analysis are well developed.    
Studies in these areas have proved their value since they both provide new    
probes of important physical processes as well as a window on physical        
processes which are less wellknown and less accessible to study by other      
techniques.  In many other areas, however, the study of comets at radio       
wavelengths continues to be primarily an exploratory endeavor.  In recognition
of this fact, the IHW Radio Science Discipline Specialist team (Table I) felt 
that it was important to attempt many different kinds of observations during  
this campaign on Halley's Comet, since each observation has scientific merit  
as an exploration.  Thus, we have been careful to document and include all    
data submitted to this archive by radio observers.                            
                                                                              
                                                                              
Table I. Discipline Specialist Team of the Radio Science Network              
___________________________________________________________________________   
                                                                              
Team Member          Affiliation                      Responsibility          
___________________________________________________________________________   
                                                                              
William M. Irvine    Astronomy Program                Discipline Specialist   
                     University of Massachusetts                              
                     Amherst, MA 01003                                        
                     U.S.A.                                                   
                                                                              
F. Peter Schloerb    Astronomy Program                Discipline Specialist   
                     University of Massachusetts                              
                                                                              
Eric Gerard          Departement de Radioastronomie   Discipline Specialist   
                     Observatoire de Meudon                                   
                     F-92190 Meudon                                           
                     France                                                   
                                                                              
Ronald D. Brown      Department of Chemistry          Discipline Specialist   
                     Monash University                  1981-85               
                     Clayton, Victoria 3168                                   
                     Australia                                                
                                                                              
Peter D. Godfrey     Department of Chemistry          Discipline Specialist   
                     Monash University                  1981-85               
                                                                              
Wayne M. Kinzel      Astronomy Program                Archive Manager         
                     University of Massachusetts                              
___________________________________________________________________________   
                                                                              
                                                                              
1.2 Radio Science Network Summary                                             
                                                                              
     The P/Halley Archive contains data from 36 different observing groups,   
representing a range of techniques.  The majority of the observational data   
comes in the well developed area of 18cm OH observations.  However, many other
projects were attempted as well.  Approximately 75% of the groups who are     
known to have obtained useful data on the comet have submitted it to the      
archive, and we are grateful to them for their contributions.                 
                                                                              
     In this document, we describe the format of the data contained in the    
Radio Science archive of observations of P/Halley.  In Sec. 2, we present a   
detailed description of the FITS files which contain the data.  Section 3     
contains a description of the Radio Science Index to the CD-ROM.  Section 4   
provides a description of the printed archive format, which may also be used  
as an index to the data under some circumstances.  The units adopted by the   
Radio Science Network are given in Sec. 5, and the calibration of data is     
discussed in Sec. 6.  Finally, in Sec. 7, we acknowledge those who have been  
so helpful to us in the construction of this archive.                         
                                                                              
                                                                              
2. THE RADIO SCIENCE FITS FORMAT                                              
                                                                              
2.1 FITS Header Description                                                   
                                                                              
     The IHW Radio Science archive is written in FITS format following the    
standard for all networks within the IHW.  FITS files are a standard for      
interchange of astronomical data.  They consist of one or more 2880-byte      
header records, which contain the documentary information about the           
observation, followed by 0 or more 2880-byte data records in the format that  
is specified by the FITS header.  In the IHW archive, these two parts of a    
FITS file, the header records and the data records, are presented in two      
different files to facilitate their use by a wide range of analysis software. 
However, we note that users who require FITS format files have only to        
concatenate the header and data files to make a standard FITS file.           
                                                                              
     The FITS header is meant to provide a description of the structure and   
format of the FITS data records that follow it and to offer any auxiliary     
information that is necessary for its interpretation.  For the Radio Science  
FITS header, we have defined several FITS keywords which specify observational
parameters that are necessary to interpret the data.  A detailed description  
of the complete Radio Science FITS header is presented in Sec. 2.1.  In       
general, the Radio Science Network has tried to conform to standards which are
commonly used in FITS and adopted by the IHW.  The characteristics of the     
observation are described by assigning values to the "keywords" which are     
described in the tables below.  We note that special keywords which we have   
defined have been selected to specify information which is vital to the       
interpretation of the data, such as specification of the observing frequncy or
telescope parameters.  At another level, under FITS HISTORY keywords, we      
present information about how the data were obtained, including calibration   
and orbital tracking information.  The distinction between these groupings is 
admittedly somewhat arbitrary and has been made primarily to limit the number 
of new FITS keywords defined by our network.                                  
                                                                              
     In an exploratory program, like the Radio Science Network, it is to be   
expected that many observations will fail to detect the comet, and the data to
be archived are best described as an upper limit rather than through          
presentation of a spectrum or image.  In recognition of this fact, the IHW    
permits FITS files to be created without any data records at all, and in this 
case, the "data" are presented as a summary in the FITS HISTORY section of the
Radio Science header.  FITS files of this type may be recognized because they 
have the NAXIS keyword set equal to 0 and the DAT-TYPE keyword set equal to   
the character string 'NODATA  '.                                              
                                                                              
     Where possible, even when actual data exist, we have attempted to        
describe them by presenting the results of a model fit to the data.  In       
spectral line work, for example, a line is often described in terms of its    
peak intensity, the velocity of the peak, the line width, the integrated area 
under the line, and the mean velocity of the emission.  We have provided these
values in FITS HISTORY keywords by fitting a gaussian line shape model to the 
data.                                                                         
                                                                              
2.1.1 Keyword block I: Basic FITS keywords                                    
                                                                              
     This block of keywords is required of FITS tapes.  The details are listed
in Table II below.                                                            
                                                                              
                                                                              
Table II. Keyword Block I                                                     
______________________________________________________________________________
                                                                              
Keyword  Type  Description                                                    
______________________________________________________________________________
                                                                              
SIMPLE    L    Conformity to basic FITS standards                             
BITPIX    I    Bits per pixel in data record                                  
NAXIS     I    Number of axes in data record; if NAXIS = 0 then no data record
NAXIS1    I    Number of pixels in row along first axis; if NAXIS1 = 0 then   
               this is Extended FITS Format and GROUP data are present        
NAXISn    I    Number of pixels along n-th axis in image                      
______________________________________________________________________________
                                                                              
                                                                              
2.1.2 Keyword block II: International Halley Watch keywords                   
                                                                              
     These keywords are agreed upon for use by the entire Halley Watch and    
they are listed in Table III.                                                 
                                                                              
                                                                              
Table III. Keyword Block II                                                   
______________________________________________________________________________
                                                                              
Keyword  Type  Description                                                    
______________________________________________________________________________
                                                                              
OBJECT    C    Name of the object                                             
                    Examples: 'P/CROMMELIN'                                   
                              'P/HALLEY'                                      
                              'P/GIACOBINI-ZINNER'                            
FILE-NUM  I    6NNNNV - unique, sequential number to identify files sent to   
                    IHW Lead Center.  Format description:                     
                    6 = denotes Radio Science Network                         
                 NNNN = unique 4 digit ID number assigned to each observation 
                    V = version number (used to keep track of resubmissions)  
DATE-OBS  C    'DD/MM/YY' - UT date of middle of observation                  
                    if observations made during several intervals, then these 
                    intervals will be specified in the HISTORY fields         
                    described below                                           
TIME-OBS  R    UT time of middle of observation expressed in decimal days     
DATE-REL  C    'DD/MM/YY' - date when observations may be publicly released   
DISCIPLN  C    'RADIO STUDIES' - the Network identification                   
LONG-OBS  C    'DDD/MM/SS' - east longitude of observatory (0-360 deg)        
LAT--OBS  C    'sDD/MM/SS' - latitude of observatory                          
SYSTEM    C    '6OOOCCTT' - system code formatted:                            
                    6 = Radio Science Network                                 
                  OOO = IAU number for observatory                            
                        (OOO = 500 for radio observatories since no IAU number
                         exists)                                              
                   CC = identifies country according to LSPN Code             
                   TT = identifies radio telescope                            
OBSERVER  C    Name of observer                                               
                    Format : 'LASTNAME,I'            - 1 author               
                             'LASTNAME,I/NEXTNAME,J' - 2 authors              
                             'LASTNAME,I/ET AL.'     - >2 authors             
                    For more than 2 observers, the names of all additional    
                    observers are given in special ADD. OBS. comments         
SUBMITTR  C    Name of submitter of data                                      
SPEC-EVT  L    Flag for special events as designated by Discipline Specialist 
DAT-FORM  C    Describes format of FITS data records                          
               'NODATA  ' - no FITS data records written                      
               'STANDARD' - data records conform to FITS standard             
               'ASCII   ' - data records are to be interpreted as logical     
                            records of 80 ASCII characters (not FITS standard)
               'HARDCOPY' - data submitted as hardcopy                        
______________________________________________________________________________
                                                                              
                                                                              
2.1.3 Keyword block III: Radio Science keywords                               
                                                                              
     These keywords are to be directly read by computers in the normal manner 
of FITS header keywords.  Some attempt has been made to choose keyword names  
that are already in use by the astronomical community.  These keywords are    
used to describe information that is vital to the data interpretation or      
potentially useful for searches of the data base (Table IV).                  
                                                                              
                                                                              
Table IV. Keyword Block III                                                   
______________________________________________________________________________
                                                                              
Keyword  Type  Description                                                    
______________________________________________________________________________
                                                                              
DIS-CODE  C    'TFESEWEABENC' - describes parameters of the                   
               telescope/instrument                                           
               T : Telescope type                                             
                    S = single antenna                                        
                    I = interferometer                                        
                    U = unknown/unclassified                                  
               FE: Frequency (Center Frequency or Rest Frequency)             
                    FE=> frequency = F x 10**(E) MHz                          
                    00=  unknown                                              
               SE: Spectral resolution                                        
                    SE=> spectral resolution = S x 10**(E) Hz                 
                    00=  unknown                                              
               WE: Bandwidth                                                  
                    WE=> bandwidth = W x 10**(E) Hz                           
                    00=  unknown                                              
               A : Beam description                                           
                    C = circular                                              
                    E = ellipitical                                           
                    O = other                                                 
                    U = unknown                                               
               BE: Beam size (geometric mean)                                 
                    BE=> beam size = B x 10**(E) arcsec                       
                    00= unknown                                               
               N : Noise estimate                                             
                    N => RMS noise = 10**(N) microJansky/beam                 
                    0 = unknown                                               
               C : Information provided by observer to Discipline Specialist  
                    is complete                                               
                    T = TRUE                                                  
                    F = FALSE                                                 
DAT-TYPE  C    'NNSTHP' - describes the data format in Header and Data Records
               NN: Subnetwork                                                 
                    OH= OH Subnetwork                                         
                         Spectral line observations of 18-cm OH               
                    SL= Spectral Line Subnetwork                              
                         Spectral line observations (other than 18-cm OH)     
                    CN= Continuum Subnetwork                                  
                         Broadband continuum observations                     
                    OC= Occultation Subnetwork                                
                         Observation of occultation events                    
                    RD= Radar Subnetwork                                      
                         Active experiments                                   
               S : Search/detection status                                    
                    S = search - implies nondetection (< 3 sigma)             
                    D = detection - implies detection (> 3 sigma)             
                    M = marginal - implies marginal detection (approx.        
                        3 sigma)                                              
               T : Type of data in FITS Data Records                          
                    N = no FITS Data Records                                  
                    S = Spectrum           => intensity vs frequency          
                    C = Continuum scan     => intensity vs space              
                    T = Time series        => intensity vs time               
                    I = Image              => spatial - spatial image         
                    D = Dynamic spectrum   => frequency - time image          
                    F = SV image           => frequency - spatial image       
                    V = Visibility Function Data                              
               H : Summary of Data in Header?                                 
                    T = Summary of data exists in Header History Section      
                    F = No summary of data in Header History Section          
               P : Polarization status                                        
                    I = Intensity data only                                   
                    P = Polarization data format used                         
OBSVTORY  C    Abbreviation for Observatory.                                  
TELESCOP  C    Telescope identifier - usually gives aperture size in meters   
LOCATION  C    Location of Observatory as given in American Ephemeris         
INSTRUME  C    'FRONT/BACK' - describes "frontend" and "backend" of receiver  
               FRONT: Receiver Front End                                      
                    MASER = Maser Amplifier                                   
                    FET   = Field Effect Transistor Amplifier                 
                    PARA  = Parametric Amplifier                              
                    MIXER = Mixer                                             
                    SPEC  = Special Front End                                 
                    UNK   = Unknown Front End                                 
               BACK  : Receiver Back End                                      
                    FB    = Filterbank                                        
                    SEFB  = Filterbank with Spectrum Expander                 
                    AC    = Autocorrelator                                    
                    CONT  = Broadband Continuum Receiver                      
                    SPEC  = Special Back End                                  
                    AOS   = Acousto-Optical Spectrometer                      
                    UNK   = Unknown Back End                                  
CENTFREQ  R    Center frequency of observed bandwidth (Hz)                    
BANDWIDT  R    Total bandwidth (Hz)                                           
BEAMSIZE  R    Geometric mean of major and minor axes of Elliptical Gaussian  
               Beam (deg)                                                     
BEAMELON  R    Ratio of major beam axis to minor beam axis                    
BEAMROTA  R    Position angle of major beam axis (deg)                        
BEAMEFF   R    Beam efficiency - fraction of power received that is in the    
               Gaussian Main Beam (BEAMEFF = 0.0 if unknown or unspecified)   
MOLECULE  C    Chemical formula for molecule (follows convention of NBS       
               interstellar-line list)                                        
TRANSITN  C    Quantum numbers for transition (follows convention of NBS      
               interstellar-line list)                                        
RESTFREQ  R    Rest frequency of line used by observer (Hz)                   
RES-SPEC  R    Spectral resolution (Hz) - true spectral resolution of the     
                 spectrometer, NOT the channel spacing                        
EQUINOX   R    Equinox of RA-DEC information presented in this file           
RAOFF     R    Pointing offset in RA direction DELTA(RA)*COS(DEC) (deg)       
DECOFF    R    Pointing Offset in Dec direction DELTA(DEC) (deg)              
DATE-BEG  C    'DD/MM/YY' - UT date on which observations began               
DATE-END  C    'DD/MM/YY' - UT date on which observations ended               
______________________________________________________________________________
                                                                              
                                                                              
2.1.4 Keyword Block IV: Special Keywords for Printed Archive                  
                                                                              
     This group of COMMENT lines give additional information to be used in the
production of the IHW printed archive.                                        
                                                                              
     The ADD. OBS. comment gives the names of the full observing team in the  
case that more than two observers carried out the observations.  More than one
ADD. OBS. comment may be used to specify teams with many members or long      
names.  The format of the ADD. OBS. comment is:                               
                                                                              
COMMENT   ADD. OBS. NAME,I/NAME2,I/NAME3,I                                    
                                                                              
     The NOTE comment provides information that is to be printed as a footnote
in the printed archive in the following format:                               
                                                                              
COMMENT   NOTE      THIS IS A TEST                                            
                                                                              
2.1.5 Keyword Block V: Radio Science Data History Section                     
                                                                              
     This block of FITS HISTORY keywords is provided to incorporate additional
information about the observation, such as descriptions of calibration methods
and sources, details about observing procedures, and comments by the observer 
and the IHW Discipline Specialist.  Another important use of the HISTORY lines
is to provide a summary of the data obtained, or in the case of FITS files    
with no data records, the actual data values reported by the observer.  The   
general format of the HISTORY lines is:                                       
                                                                              
column                                                                        
1        11        21                                                         
HISTORY   SUBKEY__  VALUES....                                                
                                                                              
where values is a list of values associated with this subkey.  In most cases, 
the value lists are in a fixed format in order to simplify their use.         
                                                                              
2.1.5.1 Data summary section                                                  
                                                                              
     In order to transmit upper limits or a summary of the data that would be 
appropriate for tabular presentation in the printed archive, we utilize one of
the following HISTORY keyword formats.  Such summaries of the data will always
be contained in the first part of the HISTORY keyword section; the presence of
such a summary shall be indicated in the DAT-TYPE keyword discussed above.  In
the case where FITS data records accompany the header, USERS OF THE ARCHIVE   
ARE CAUTIONED THAT THE SUMMARY VALUES ARE ONLY MEANT TO DESCRIBE AND          
CHARACTERIZE THE DATA ... NOT TO REPLACE THEM.                                
                                                                              
     All summary lines follow the same general form:                          
                                                                              
HISTORY   SUBKEY    ################  'UNITS   '                              
                                                                              
where the # field is a right justified floating point number.                 
                                                                              
     Format for Upper Limits:                                                 
                                                                              
COMMENT             *SUMMARY OF DATA - UPPER LIMIT                            
HISTORY   LIMIT                  0.5  'JY/BEAM '                              
                                                                              
     Upper limits in the Radio Science Network are always given as 3 standard 
deviation upper limits.                                                       
                                                                              
     Format for Spectral Lines:                                               
                                                                              
COMMENT             *SUMMARY OF DATA - SPECTRAL LINE                          
HISTORY   LINEPEAK               0.5  'JY/BEAM '                              
HISTORY   ERR-PEAK               0.1  'JY/BEAM '                              
HISTORY   LINE-VEL              10.0  'M/SEC   '                              
HISTORY   ERR--VEL             200.2  'M/SEC   '                              
HISTORY   LINE-WID            2532.0  'M/SEC   '                              
HISTORY   ERR--WID             130.2  'M/SEC   '                              
HISTORY   LINEAREA            1243.1  'JY/B*M/S'                              
HISTORY   ERR-AREA             143.6  'JY/B*M/S'                              
HISTORY   LINEMEAN              32.1  'M/SEC   '                              
HISTORY   ERR-MEAN              10.2  'M/SEC   '                              
                                                                              
The spectral line summary values LINEPEAK, LINE-VEL, and LINE-WID are         
determined from gaussian fits to the line profiles.  If one or more parameters
were fixed in a fit to the data, the assumed values are listed with no errors.
Spectral lines with hyperfine structure (e.g., HCN) are fitted on the         
assumption that all hyperfine components have their nominal intensity ratios. 
                                                                              
     Format for Continuum Observations:                                       
                                                                              
COMMENT             *SUMMARY OF DATA - CONTINUUM                              
HISTORY   CONTFLUX               0.5  'JY/BEAM '                              
HISTORY   ERR-FLUX               0.1  'JY/BEAM '                              
                                                                              
     Format for Radar Observations:                                           
                                                                              
COMMENT             *SUMMARY OF DATA - RADAR                                  
HISTORY   XSECTION              30.0  'SQUARE KILOMETERS'                     
HISTORY   ERR-XSEC               6.0  'SQUARE KILOMETERS'                     
                                                                              
2.1.5.2 Observing window section                                              
                                                                              
     Since many radio observations take place over several days, we include   
the precise observing windows in the HISTORY section according to the format: 
                                                                              
COMMENT             *OBSERVING WINDOW SPECIFICATION                           
HISTORY   N-WINDOW                 #                                          
HISTORY   WINDOW    'DD/MM/YY' #######     'DD/MM/YY' #######                 
HISTORY   WINDOW    'DD/MM/YY' #######     'DD/MM/YY' #######                 
                                                                              
where N-WINDOW gives the total number of windows for observation and          
subsequent window lines give the date and time (in decimals as in TIME-OBS) of
beginning and end of the observing window.  The time fields are right         
justified floating point numbers.                                             
                                                                              
2.1.5.3 Orbital elements section                                              
                                                                              
          Radio observers track the comet "blind" and it is important to know 
the precise position on the sky that they were tracking.  We include a        
provision in the HISTORY section to specify the two-body elements and         
observatory position data used to produce the topocentric ephemeris for       
tracking.                                                                     
                                                                              
COMMENT             *ORBITAL ELEMENT SPECIFICATION                            
HISTORY   ORBELEM                  T      - T if orbital elements are         
                                            provided                          
HISTORY   LONGEAST      243.11046715      - east longitude of observatory     
                                            (deg)                             
HISTORY   RHO--COS      0.8159113419      - radius*cos(lat) for observatory   
                                            (units of Earth equatorial        
                                            radius)                           
HISTORY   RHO--SIN      0.5765085118      - radius*sin(lat) for observatory   
                                            (units of Earth equatorial        
                                            radius)                           
HISTORY   ET-UT             53.18439      - Ephemeris Time - UT correction (s)
HISTORY   JD           2446471.16128      - Time of Perihelion passage (ET)   
HISTORY   Q                0.5870959      - Perihelion Distance (AU)          
HISTORY   E                0.9672671      - Eccentricity                      
HISTORY   SOMEGA           111.85336      - Arg. of Perihelion (deg)          
HISTORY   LOMEGA            58.15313      - Long. of Ascending Node (deg)     
HISTORY   I                162.23779      - Inclination (deg)                 
                                                                              
2.1.5.4 Antenna tracking section                                              
                                                                              
     This HISTORY keyword specifies the antenna rms pointing errors.          
                                                                              
COMMENT             *RMS POINTING ERROR OF TELESCOPE                          
HISTORY   POINTERR  ################ 'UNITS   '                               
                                                                              
2.1.5.5 Calibration section                                                   
                                                                              
     This group of keywords provides information on details of the calibration
process.                                                                      
                                                                              
COMMENT             *CALIBRATION METHOD INFORMATION                           
HISTORY   CALMETH   'DESCRIPTION OF CAL METHOD'                               
                                                                              
If the calibration method is unknown, then no line appears.  Current possible 
values are 'CHOPPER WHEEL', 'NOISE TUBE', 'STANDARDS', 'ABSOLUTE'.            
                                                                              
COMMENT             *CALIBRATION STANDARD INFORMATION                         
HISTORY   CALSRCE   'SOURCE NAME'    ########## 'UNITS   '                    
                                                                              
Source (or sources) used to provide principal calibration.  The # field is a  
right justified floating point number. For planets as the calibrators, the    
assumed brightness temperature is given; otherwise, the calibrator flux       
density is given in Jansky.  There may be more than one CALSRCE HISTORY line. 
                                                                              
COMMENT             *SYSTEM TEMPERATURE ETC.                                  
HISTORY   TSYSTEM   ############### '_SB     '                                
HISTORY   TRCVR     ############### '_SB     '                                
                                                                              
Total system temperature (TSYSTEM) and noise temperature of the reciver alone 
(TRCVR).  '_SB     ' allows single side band measurement ('SSB     ') or      
double sideband measurement ('DSB     ') to be indicated.  The # field is a   
right justified floating point number.                                        
                                                                              
HISTORY   TAUZENTH  ###############                                           
                                                                              
Atmospheric opacity at zenith.  The # field is a right justified floating     
point number.                                                                 
                                                                              
2.1.5.6 Observer's comment section                                            
                                                                              
     This block of HISTORY lines contains any extra comments about conditions,
data quality, etc. that are sent to the Discipline Specialist by the observer.
There are generally fewer than eight such comment lines given.                
                                                                              
COMMENT             *OBSERVER COMMENTS                                        
HISTORY   OBSCOMM   ROOM TO REPORT OBSERVER COMMENTS                          
HISTORY   OBSCOMM   ...                                                       
HISTORY   OBSCOMM   ...                                                       
HISTORY   OBSCOMM   MORE ROOM FOR OBSERVER COMMENTS                           
                                                                              
2.1.5.7 Discipline Specialist's comment section                               
                                                                              
     Comments by the Discipline Specialist team on this observation.  There   
are generally fewer than eight such comment lines given.                      
                                                                              
COMMENT             *DISCIPLINE SPECIALIST COMMENTS                           
HISTORY   DSCOMM    ROOM TO REPORT DISCIPLINE SPECIALIST COMMENTS             
HISTORY   DSCOMM    ...                                                       
HISTORY   DSCOMM    ...                                                       
HISTORY   DSCOMM    MORE ROOM FOR DISCIPLINE SPECIALIST COMMENTS              
                                                                              
2.1.6 Keyword block VI: Standard FITS keywords                                
                                                                              
     These keywords are used to describe the FITS data records.  They are all 
standard and they are summarized in Table V.                                  
                                                                              
                                                                              
Table V.  Keyword Block VI                                                    
______________________________________________________________________________
                                                                              
Keyword  Type  Description                                                    
______________________________________________________________________________
                                                                              
BSCALE    R    Scale factor  data = tape * BSCALE + BZERO                     
BZERO     R    Zero value                                                     
BUNIT     C    Units of data                                                  
               'JY/BEAM ' - for line and continuum data                       
               'STANDARD DEVIATIONS' - for radar data                         
BLANK     I    Value for out-of-range data                                    
CRVALn    R    Value of physical coordinate of nth axis at the reference pixel
CRPIXn    R    Array location of reference pixel for nth axis                 
CDELTn    R    Increment in physical coordinate along nth axis                
CTYPEn    C    Type of physical coordinate                                    
               'VELO-COM' - frequency coordinate for line work in m/s defined 
                            to be velocity relative to the comet              
               'VELO-GEO' - velocity defined relative to center of Earth      
               'FREQUENCY' - frequency offset of radar echo from expected     
                             value in units of Hz                             
               'CIRCULAR POLARIZATION' - axis used to define different states 
                                         of circular polarization: -1 = LHC;  
                                         -2 = RHC                             
               'LINEAR POLARIZATION' - axis used to define linear polarization
                                       position angle                         
               'ECHO POLARIZATION' - axis used to define polarization of radar
                                     echo                                     
               'RAOFF   ' - spatial coordinate for maps (deg)                 
               'DECOFF  ' - spatial coordinate for maps (deg)                 
               'RA      ' - coordinate used for drift scans (deg)             
               'MAP-TYPE' - coordinate to indicate type of drift scan map:    
                            0 = map with comet in beam; 1,2 = maps of galactic
                            background only                                   
CROTAn    R    Rotation angle of physical coordinate axis n                   
______________________________________________________________________________
                                                                              
                                                                              
2.1.7 Keyword block VII: End statement                                        
                                                                              
     This keyword is required by FITS to terminate the header:                
                                                                              
END                                                                           
                                                                              
2.2 Types of Data in the P/Halley Archive.                                    
                                                                              
     Several distinct types of data were obtained during the International    
Halley Watch, and each data type required the use of a slightly different type
of FITS format.  In this section, we review the individual data types and any 
special steps taken in formatting data of this type.                          
                                                                              
2.2.1 Upper limits                                                            
                                                                              
     As stated above in the description of the FITS format, upper limits are  
reported in the HISTORY section of the FITS header in the HISTORY LIMIT       
keyword. The detection status of a particular observation is summarized in the
third character of the DAT-TYPE keyword.  An S implies that the observation   
did not yield a detection and is reported as a limit.  However, in some cases 
marginal results, designated by M in the DAT-TYPE keyword have also been      
reported as limits.                                                           
                                                                              
2.2.2 OH spectral line observations                                           
                                                                              
     The principal type of data is the 18-cm OH observations.  These data are 
archived in FITS format as one-dimensional spectra of the flux density of the 
comet as a function of the line of sight velocity.  For most OH observations, 
the line of sight velocity is given with respect to the observer, although    
some observers transmitted their results to us in terms of the geocentric     
velocity.                                                                     
                                                                              
     Many OH line observations were conducted using two receivers having      
orthogonal polarizations.  In order to preserve this information, we have     
presented the polarized spectral data in a two dimensional format with a      
second axis to designate which polarization applies.  These spectra will have 
the NAXIS keyword set equal to 2, and the second axis will be labeled either  
'CIRCULAR POLARIZATION' or 'LINEAR POLARIZATION', as shown in Table V above.  
This method for designating polarization is similar to the convention used in 
many FITS formats, where a separate axis (often labeled 'STOKES') is used to  
give the full Stokes parameters of the data.  However, full Stokes parameters 
have not measured in this archive, and so we have defined these new           
polarization axes to handle this situation.                                   
                                                                              
2.2.3 Interferometric UV data                                                 
                                                                              
     Radio interferometers measure a source's visibility function, which is   
the Fourier transform of the source brightness distribution.  In aperture     
synthesis imaging, a set of measurements of the visibility function are       
Fourier transformed to obtain an image of the source brightness distribution. 
Unfortunately, the processing steps required to make a map force the observer 
to specify many parameters that determine how the visibility data will be     
transformed to make the image.  The specification of these parameters and the 
Fourieer transformation of the data, in our view, constitutes an              
interpretation of the data, and runs counter to the philosophy of a data      
archive.  Thus, we have preserved the actual visibility data in this archive. 
                                                                              
     The visibility data are presented in the extended FITS GROUP data format.
This is the format currently used for visibility data by many of the world's  
interferometers, and FITS readers for visibility data should be able to read  
the files prepared for the IHW archive directly.  We have tested the files in 
the data reduction program for the U.S. National Radio Astronomy Observatory  
(Astronomical Image Processing System = AIPS), and in fact the files are quite
similar to the UVFITS format of AIPS.  For spectral line data, AIPS cannot    
Fourier transform more than eight spectral line channels at a time.           
Therefore, following the style of the NRAO VLA, we have archived the 32       
channel data that were typically obtained in 4 separate FITS files with 8     
channels in each file. A fifth file usually accompanies this data and contains
the broadband continuum data recorded at the same time as the spectral line   
data.                                                                         
                                                                              
2.2.4 Radar data                                                              
                                                                              
     Radar observations of Halley's Comet were carried out only at the Arecibo
Observatory during November 1985.  We have recorded the average echo obtained 
during this experiment in a single FITS file.  The radar observation is made  
by transmitting a single frequency tone in one circular polarization toward   
the comet and observing the echo in both polarizations.  The echo is observed 
in spectral line mode, and a detection is sought at the correct Doppler       
shifted frequency given by the ephemeris of the comet.  Thus, since this data 
type is identical in most respects to a spectral line observation, the data   
are recorded in a similar format.  For a specular reflection, the echo is     
expected to be polarized in the sense opposite to that of the transmitted     
signal.  However, real surfaces often contain significant power in the same   
sense as that trans- mitted, perhaps due to multiple reflections on the       
target.  We have treated the echo polarization in the same manner as the      
orthogonal polarizations in the OH experiments, but with a special key to     
designate the "same" and the "opposite" senses of polarization.               
                                                                              
2.2.5 Occultations                                                            
                                                                              
     Many occultation-type experiments were carried out during the Halley     
campaign.  Unfortunately, relatively few were reported to the International   
Halley Watch for inclusion in this archive.  The occultation data that are    
presented here employed the Milky Way itself as a background source and made  
observations of a track across the sky with and without the comet present in  
the beam.  When carried out as a spectral line experiment, these data result  
in a two dimensional data type with spectra taken at many positions along a   
track on the sky.  We have attempted to preserve the raw data here by saving  
these two dimensional images in the FITS file.  Thus, a typical file contains:
(1) the data with the comet in the beam; (2) one or more maps with the comet  
out of the beam, which were obtained on a different day.  We have chosen to   
present these different maps as a three dimensional "cube" of data, with      
NAXIS = 3.  The first axis is the frequency dimension of the spectra.  The    
second axis is the position of the spectrum in RA.  Finally, the third axis,  
labeled 'MAP-TYPE' defines which map is being presented.  MAP-TYPE = 0 is the 
data with the comet in the beam, and MAP-TYPE not equal to 0 gives the map of 
the galactic background alone on one or more days of observation.  Users are  
advised to check the individual FITS headers for further information on the   
definition of MAP-TYPE for specific dates of observation.                     
                                                                              
                                                                              
3. THE RADIO SCIENCE NETWORK INDEX TO THE CD-ROMS                             
                                                                              
     The IHW provides various indices to help users of the archive find the   
data that they want.  For the Radio Science Network, there are two indices    
provided by the project which users will find useful: the quick look index and
the printed archive (see Sec. 4 for a description), both of which contain     
information on all observations in the archive.  The Radio Science Network    
provides a third, discipline specific, index which contains much more detailed
information about the radio observations than the others.  In selecting the   
information to be included in the Radio Science Index, we have attempted to   
include all relevant data from the FITS headers, within limitations imposed by
standards set by the Halley Watch.  The detailed format of the Radio Science  
index is given in Table VI.                                                   
                                                                              
                                                                              
Table VI.  IHW Radio Science Network Index Format                             
______________________________________________________________________________
                                                                              
Field    Keyword            Type  Format    Notes                             
______________________________________________________________________________
                                                                              
   1     OBJECT              C    A20                                         
   2     FILE-NUM            N    I6                                          
   3     DATE-OBS            D    A8        IHW Date Format                   
   4     TIME-OBS            N    F6.3                                        
   5     LONG-OBS            C    A9                                          
   6     LAT-OBS             C    A9                                          
   7     SYSTEM              C    A8                                          
   8     OBSERVER            C    A24                                         
   9     COMMENT  ADD. OBS.  C    A60       May exclude some observers        
  10     SUBMITTR            C    A24                                         
  11     SPEC-EVT            L    L1                                          
  12     DAT-FORM            C    A8                                          
  13     DIS-CODE            C    A12                                         
  14     DAT-TYPE            C    A6                                          
  15     OBSVTORY            C    A10                                         
  16     TELESCOP            C    A10                                         
  17     LOCATION            C    A30                                         
  18     INSTRUME            C    A20                                         
  19     CENTFREQ            N    F11.4     in MHz                            
  20     BANDWIDT            N    F11.4     in MHz                            
  21     BEAMSIZE            N    F6.4                                        
  22     BEAMELON            N    F6.3                                        
  23     BEAMROTA            N    F6.1                                        
  24     BEAMEFF             N    F6.3                                        
  25     EQUINOX             N    F8.3                                        
  26     RAOFF               N    F7.4                                        
  27     DECOFF              N    F7.4                                        
  28     MOLECULE            C    A10                                         
  29     TRANSITN            C    A20                                         
  30     RESTFREQ            N    F11.4     in MHz                            
  31     RES-SPEC            N    F11.4     in kHz                            
  32     HISTORY  LIMIT      N    F11.4     in Jy/Beam                        
  33     HISTORY  LINEPEAK   N    F11.4     in Jy/Beam                        
  34     HISTORY  ERR-PEAK   N    F11.4     in Jy/Beam                        
  35     HISTORY  LINE-VEL   N    F11.4     in m/s                            
  36     HISTORY  ERR--VEL   N    F11.4     in m/s                            
  37     HISTORY  LINE-WID   N    F11.4     in m/s                            
  38     HISTORY  ERR--WID   N    F11.4     in m/s                            
  39     HISTORY  LINEAREA   N    F11.4     in Jy/Beam * m/s                  
  40     HISTORY  ERR-AREA   N    F11.4     in Jy/Beam * m/s                  
  41     HISTORY  LINEMEAN   N    F11.4     in m/s                            
  42     HISTORY  ERR-MEAN   N    F11.4     in m/s                            
  43     HISTORY  CONTFLUX   N    F11.4     in Jy/Beam                        
  44     HISTORY  ERR-FLUX   N    F11.4     in Jy/Beam                        
  45     DATE-BEG            D    A8        Date Format                       
  46     DATE-END            D    A8        Date Format                       
  47     HISTORY  NWINDOW    N    I2                                          
  48     HISTORY  WINDOW (1) D    A8        Start Date of 1st Window (Date    
                                            Fmt)                              
  49     HISTORY  WINDOW (1) N    F5.3      Start Time of 1st Window          
  50     HISTORY  WINDOW (N) D    A8        End Date of Last Window (Date Fmt)
  51     HISTORY  WINDOW (N) N    F5.3      End Time of Last Window           
  52     HISTORY  POINTERR   N    F10.2     in arcsec                         
  53     HISTORY  CALMETH    C    A20                                         
  54     HISTORY  CALSRCE (1)C    A15       Name of Cal Source 1              
  55     HISTORY  CALSRCE (1)N    F10.3     Value of Cal Source 1             
  56     HISTORY  CALSRCE (1)C    A15       Units of Cal Source 1             
  57     HISTORY  CALSRCE (2)C    A15       Name of Cal Source 2              
  58     HISTORY  CALSRCE (2)N    F10.3     Value of Cal Source 2             
  59     HISTORY  CALSRCE (2)C    A15       Units of Cal Source 2             
  60     HISTORY  TSYSTEM    N    F7.1      Value Only                        
  61     HISTORY  TRCVR      N    F7.1      Value Only                        
  62     HISTORY  TAUZENTH   N    F4.2                                        
  63     BITPIX              N    I2                                          
  64     NAXIS               N    I2                                          
  65     BSCALE              N    F15.9                                       
  66     BZERO               N    F10.4                                       
  67     BUNIT               C    A15                                         
  68     BLANK               N    I6                                          
  69     DATAMAX             N    F10.4                                       
  70     DATAMIN             N    F10.4                                       
  71     NAXIS1              N    I4                                          
  72     CDELT1              C    A15                                         
  73     CRPIX1              C    A15                                         
  74     CRVAL1              C    A15                                         
  75     CTYPE1              C    A25                                         
  76     NAXIS2              N    I4                                          
  77     CDELT2              C    A15                                         
  78     CRPIX2              C    A15                                         
  79     CRVAL2              C    A15                                         
  80     CTYPE2              C    A25                                         
  81     NAXIS3              N    I4                                          
  82     CDELT3              C    A15                                         
  83     CRPIX3              C    A15                                         
  84     CRVAL3              C    A15                                         
  85     CTYPE3              C    A25                                         
  86     NAXIS4              N    I4                                          
  87     CDELT4              C    A15                                         
  88     CRPIX4              C    A15                                         
  89     CRVAL4              C    A15                                         
  90     CTYPE4              C    A25                                         
  91     NAXIS5              N    I4                                          
  92     CDELT5              C    A15                                         
  93     CRPIX5              C    A15                                         
  94     CRVAL5              C    A15                                         
  95     CTYPE5              C    A25                                         
  96     NAXIS6              N    I4                                          
  97     CDELT6              C    A15                                         
  98     CRPIX6              C    A15                                         
  99     CRVAL6              C    A15                                         
 100     CTYPE6              C    A25                                         
 101     PATH:VOLUME         C    A8        CD-ROM VOLUME NAME                
 102     PATH:YEAR SUBDIRECT C    A5        YEAR  SUBDIRECTORY                
 103     PATH:MON. SUBDIRECT C    A3        MONTH SUBDIRECTORY                
 104     PATH:DAY  SUBDIRECT C    A3        DAY   SUBDIRECTORY                
 105     PATH:HOUR SUBDIRECT C    A3        HOUR  SUBDIRECTORY                
 106     FILENAME            C    A8        FILENAME                          
______________________________________________________________________________
                                                                              
                                                                              
4. THE RADIO SCIENCE NETWORK PRINTED ARCHIVE                                  
                                                                              
     In addition to the FITS presentation of the Radio Science Network data,  
an additional format is available in the printed archive.  This format        
provides most of the information that is necessary to make use of the data, as
well as the "data summary" information included in the FITS headers, such as  
the line peak intensity and width for spectral line observations.  The format 
of the printed archive for the Radio Science Network is shown below.          
                                                                              
4.1 Printed Format I: OH Subnetwork and Spectral Line Subnetwork              
                                                                              
     Since the OH Subnetwork and the Spectral Line Subnetwork contain the same
data type, it is most economical to print both subnetworks together in the    
same subsection of the Radio Science part of the archive.  Detailed           
description of this format is in Table VII.                                   
                                                                              
                                                                              
Table VII.  Printed Format I                                                  
______________________________________________________________________________
                                                                              
Col.  FITS                        Field        Field         Notes            
      Keywords                    Format       Header                         
______________________________________________________________________________
                                                                              
  1   DATE-OBS,TIME-OBS          DD.TTTTT      Date(UT)                       
 10   FILE-NUM                      I6         RSN#                           
 17   MOLECULE                      A5         Mol                            
 23   DAT-TYPE (4th character)      A1         DT           Denotes Subnetwork
 25   RESTFREQ (MHz)                I6         Freq                           
 32   RES-SPEC (kHz)                I4         Res                            
 37   HISTORY  TSYSTEM (K)          I5         Tsys                           
 43   BEAMEFF (per cent)            I2         BE                             
 46   BEAMSIZE (arcsec)             I4         HP                             
 51   DIS-CODE (8th character)      A1         BS           Denotes beam shape
 53   Radial Offset of              I4         rho                            
      Beam from Nucleus (arcsec)                                              
 58   Position Angle of             I3         PA                             
      Radial Offset (deg)                                                     
                                                                              
      For Limits:                                                             
                                                                              
 62   A "<" symbol                  A1                                        
 63   HISTORY  LIMIT (Jy/Beam)      F6.1       Line Peak    if value>10Jy/Beam
                                 or F6.3                    if value<10Jy/Beam
 80   A "-" symbol                  A1         Width                          
 91   A "-" symbol                  A1         Velocity                       
                                                                              
      For Detections:                                                         
                                                                              
 63   HISTORY  LINEPEAK (Jy/Beam)   F6.1                    if value>10Jy/Beam
                                 or F6.3                    if value<10Jy/Beam
 69   A "plus or minus" symbol      A1         Line Peak                      
 70   HISTORY ERR-PEAK (Jy/Beam)    F5.1                    if value>10Jy/Beam
                                 or F5.3                    if value<10Jy/Beam
 76   HISTORY  LINE-WID (km/sec)    F4.2                                      
 80   A "plus or minus" symbol      A1         Width                          
 81   HISTORY  ERR--WID (km/sec)    F4.                                       
 86   HISTORY  LINE-VEL (km/sec)    F5.2                                      
 91   A "plus or minus" symbol      A1         Velocity                       
 92   HISTORY  ERR--VEL (km/sec)    F4.2                                      
                                                                              
      For All:                                                                
                                                                              
 97   SYSTEM                        A8         System                         
106   OBSERVER                      A23        Observer                       
130   COMMENT NOTE                  A2         Note                           
______________________________________________________________________________
                                                                              
                                                                              
4.2 Printed Format II: Continuum Subnetwork                                   
                                                                              
     The data in the continuum subnetwork are fundamentally different from the
spectral line data in the previous section.  Thus they require anopther       
format, listed in Table VIII.                                                 
                                                                              
                                                                              
Table VIII.  Printed Format II                                                
______________________________________________________________________________
                                                                              
Col.  FITS                        Field        Field         Notes            
      Keywords                    Format       Header                         
______________________________________________________________________________
                                                                              
  1   DATE-OBS,TIME-OBS          DD.TTTTT      Date(UT)                       
 11   FILE-NUM                      I6         RSN#                           
 18   DAT-TYPE (4th character)      A1         DT           Denotes Subnetwork
 20   CENTFREQ (MHz)                I6         Freq                           
 27   BANDWIDT (MHz)                I4         Res                            
 34   HISTORY  TSYSTEM              I5         Tsys                           
 40   BEAMEFF (per cent)            I2         BE                             
 43   BEAMSIZE (arcsec)             I4         HP                             
 48   DIS-CODE (8th character)      A1         BS           Denotes Beam Shape
 50   Radial Offset of              I4         rho                            
      Beam from Nucleus (arcsec)                                              
 55   Position Angle of             I3         PA                             
      Radial Offset (deg)                                                     
                                                                              
      For Limits:                                                             
                                                                              
 60   A "<" Symbol                  A1                                        
 61   HISTORY  LIMIT (Jy/Beam)      F6.1       Flux Density if value>10Jy/Beam
                                 or F6.3                    if value<10Jy/Beam
                                                                              
      For Detections:                                                         
                                                                              
 61   HISTORY CONTFLUX (Jy/Beam)    F6.1                    if value>10Jy/Beam
                                 or F6.3                    if value<10Jy/Beam
 67   A "plus or minus" symbol      A1         Flux Density                   
 68   HISTORY ERR-FLUX (Jy/Beam)    F5.1                    if value>10Jy/Beam
                                 or F5.3                    if value<10Jy/Beam
                                                                              
      For All:                                                                
                                                                              
 75   SYSTEM                        A8         System                         
 84   OBSERVER                      A30        Observer                       
116   COMMENT NOTE                  A2         Note                           
______________________________________________________________________________
                                                                              
                                                                              
4.3 Printed Format III: Occultation Subnetwork                                
                                                                              
     Since the occultation data in this archive is of the same type as the OH 
and Spectral Line Subnetworks, they are presented in the same format.         
Detailed description is in Table IX.                                          
                                                                              
                                                                              
Table IX. Printed Format III                                                  
______________________________________________________________________________
                                                                              
Col.  FITS                        Field        Field         Notes            
      Keywords                    Format       Header                         
______________________________________________________________________________
                                                                              
  1   DATE-OBS,TIME-OBS          DD.TTTTT      Date(UT)                       
 10   FILE-NUM                      I6         RSN#                           
 17   MOLECULE                      A5         Mol                            
 23   DAT-TYPE (4th Character)      A1         DT           Denotes Subnetwork
 25   RESTFREQ (MHz)                I6         Freq                           
 32   RES-SPEC (MHz)                I4         Res                            
 37   HISTORY  TSYSTEM (K)          I5         Tsys                           
 43   BEAMEFF (per cent)            I2         BE                             
 46   BEAMSIZE (arcsec)             I4         HP                             
 51   DIS-CODE (8th Character)      A1         BS           Denotes Beam Shape
 53   Radial Offset of              I4         rho                            
      Beam from Nucleus (arcsec)                                              
 58   Position Angle of             I3         PA                             
      Radial Offset (deg)                                                     
                                                                              
      For Limits:                                                             
                                                                              
 62   A "<" symbol                  A1                                        
 63   HISTORY  LIMIT (Jy/Beam)      F6.1       Line Peak    if value>10Jy/Beam
                                 or F6.3                    if value<10Jy/Beam
 80   A "-" symbol                  A1         Width                          
 91   A "-" symbol                  A1         Velocity                       
                                                                              
      For Detections:                                                         
                                                                              
 63   HISTORY LINEPEAK (Jy/Beam)    F6.1                    if value>10Jy/Beam
                                 or F6.3                    if value<10Jy/Beam
 69   A "plus or minus" symbol      A1         Line Peak                      
 70   HISTORY ERR-PEAK (Jy/Beam)    F5.1                    if value>10Jy/Beam
                                 or F5.3                    if value<10Jy/Beam
 76   HISTORY  LINE-WID (km/sec)    F4.2                                      
 80   A "plus or minus" symbol      A1         Width                          
 81   HISTORY  ERR--WID (km/sec)    F4.2                                      
 86   HISTORY  LINE-VEL (km/sec)    F5.2                                      
 91   A "plus or minus" symbol      A1         Velocity                       
 92   HISTORY  ERR--VEL (km/sec)    F4.2                                      
                                                                              
      For All:                                                                
                                                                              
 97   SYSTEM                        A8         System                         
106   OBSERVER                      A23        Observer                       
130   COMMENT NOTE                  A2         Note                           
______________________________________________________________________________
                                                                              
                                                                              
4.4 Printed Format IV: Radar Subnetwork                                       
                                                                              
     There is only one radar observation in the archive, but for consistency  
we have made a printed format for it.  The format follows the Continuum       
Subnetwork format and is described in Table X.                                
                                                                              
                                                                              
Table X. Printed Format IV                                                    
______________________________________________________________________________
                                                                              
Col.  FITS                        Field        Field         Notes            
      Keywords                    Format       Header                         
______________________________________________________________________________
                                                                              
  1   DATE-OBS,TIME-OBS          DD.TTTTT      Date(UT)                       
 10   FILE-NUM                      I6         RSN#                           
 18   DAT-TYPE (4th character)      A1         DT           Denotes Subnetwork
 20   CENTFREQ (MHz)                I6         Freq                           
 27   BANDWIDT (MHz)                I4         Res                            
 34   HISTORY  TSYSTEM              I5         Tsys                           
 40   BEAMEFF (per cent)            I2         BE                             
 43   BEAMSIZE (arcsec)             I4         HP                             
 48   DIS-CODE (8th character)      A1         BS           Denotes Beam Shape
 50   Radial Offset of              I4         rho                            
      Beam from Nucleus (arcsec)                                              
 55   Position Angle of             I3         PA                             
      Radial Offset (deg)                                                     
 61   HISTORY XSECTION              F6.1                                      
 67   A "plus or minus" symbol      A1         Cross Sect.   In units of km**2
 68   HISTORY ERR-XSEC              F5.1                                      
 75   SYSTEM                        A8         System                         
 84   OBSERVER                      A30        Observer                       
116   COMMENT NOTE                  A2         Note                           
______________________________________________________________________________
                                                                              
                                                                              
5. UNITS IN THE RADIO SCIENCE ARCHIVE                                         
                                                                              
     We have attempted to use a fixed set of standard units for the values    
given in the IHW archive.  These units are given in Table XI.  Where these    
units are not used, as in the printed archive, the index tables, or in certain
values in the HISTORY section of the FITS headers, attention is explicitly    
called to the change of units.                                                
                                                                              
                                                                              
Table XI. IHW Radio Science Units                                             
_______________________________________                                       
                                                                              
Angle                           Degrees                                       
Length                           Meters                                       
Time                            Seconds                                       
Frequency                         Hertz                                       
Velocity                  Meters/Second                                       
Flux Density               Jansky/Beam*                                       
Radar Cross Section   Square kilometers                                       
_______________________________________                                       
                                                                              
* 1 Jansky = 1.0 x 10(-26) Watts per                                          
  square meter per Hertz                                                      
                                                                              
     The adoption of the flux density unit, Jansky per beam, deserves some    
additional comment.  This unit is well defined: the signal is described in    
terms of the flux density of a point source which would produce the same      
signal observed from the comet.  The explicit use of "per beam" in the unit   
acknowledges that the coma is possibly resolved by the beam to an unknown     
extent.  Some observatories, such as the VLA, have naturally already adopted  
this choice of units since they use celestial point sources to calibrate the  
instrument.  All continuum observations also use Janskys to express their     
results regardless of how the data are actually internally calibrated.  Thus, 
in both of these cases, the Jansky is the obvious choice of unit.  For        
spectral line work on large single antennas, however, results are typically   
expressed in "antenna temperature" since they are calibrated by comparing the 
observed signal to a calibration signal of known noise temperature.  In recent
years, this unit has become rather confusing as a result of efforts to convert
a relatively well defined observed quantity into a more physically meaningful 
unit which gives an approximation to the true brightness temperature of the   
source.  Thus, various forms of "corrected" antenna temperature are in use at 
different observatories, and it is often not clear which corrections have been
made to the data.  We therefore favor a system in which the calibration is    
achieved by direct comparison of the cometary signal to celestial sources of  
known flux density, and the natural unit for such a comparison is the unit of 
flux density, the Jansky.  Thus, all observations in the archive have been    
converted to these units using data provided by the observers.                
                                                                              
                                                                              
6. CALIBRATION                                                                
                                                                              
     Although we have converted the data in the archive to a common unit of   
flux density, we have made no attempt to recalibrate data to a common flux    
density scale.  The calibration scale for radio astronomy is well established 
at centimeter wavelengths, and in general, well known standard sources were   
used by the network observers.  For wavelengths shorter than about 1          
centimeter, however, the calibration becomes less precise as atmospheric      
attenuation  becomes significant in the observations. In most cases,          
comparisons to celestial sources are more indirect and observers rely on      
absolute calibration schemes as their primary method.  Ultimately, though,    
even these techniques use known sources, such as the planets, to calibrate the
system, and we have attempted to archive information about these calibration  
sources with each observation.                                                
                                                                              
     Calibration information that is supplied to us by the observer is given  
in the HISTORY section of the FITS header.  The HISTORY  CALMETH keyword      
provides an ASCII string with a brief description of the calibration method   
used.  Three methods are commonly used: (1) STANDARDS indicates that the data 
were calibrated through direct comparison to standard sources; (2) NOISE TUBE 
indicates that the data were primarily calibrated by injecting power from a   
noise source into the receiver; (3) CHOPPER WHEEL indicates that the "chopper 
wheel" method was used; (4) ABSOLUTE calibration is used for the radar        
observations presented in this archive and is based on measurements of antenna
and transmitter properties rather than on astronomical standards.  This latter
method uses the comparison of the noise power from an ambient temperature load
to that produced by the sky emission to make an estimate of the optical depth 
of the atmosphere, and it is commonly used at millimeter wavelengths.         
                                                                              
     Even in the cases of NOISE TUBE and CHOPPER WHEEL calibration, where     
celestial sources are not initially used to calibrate the data, the final     
calibration is generally made with celestial sources.  Whenever a standard    
source is used for this purpose, its name and assumed flux density are given  
in the HISTORY  CALSRCE keywords.  More than one of these keywords may exist  
in the header if more than one calibration source is used.  For planetary     
sources, the assumed brightness temperature is given rather than the flux     
density since planetary flux densities vary with distance to the object.      
Finally, the system temperature (defined to be the total system noise         
temperature including receiver noise and atmospheric and ground pickup) and   
the receiver temperature (defined to be the noise temperature of the receiver 
alone) are given in the HISTORY  TSYSTEM and HISTORY  TRCVR keywords; the     
atmospheric opacity at zenith is given in the HISTORY  TAUZENTH keyword where 
appropriate.                                                                  
                                                                              
                                                                              
7. THE OBSERVERS                                                              
                                                                              
     Many people have made substantial contributions to the success of the    
Radio Science Network of the International Halley Watch.  First of all, we    
wish to thank the observers who have submitted data to the archive, since     
if it were not for their interest and assistance, there would be no archive   
at all.  These observers are listed in Table XII.  We also appreciate those   
who attempted to observe comet P/Halley even if they did not get useful data. 
In many cases, these early attempts paid off in our later studies of comet    
Halley.                                                                       
                                                                              
                                                                              
Table XII. IHW Radio Science Observers                                        
_____________________________________________________________________________ 
                                                                              
Observer             Affiliation                                              
_____________________________________________________________________________ 
                                                                              
Abraham, Z.          Instituto de Pesquisas Espaciais, Brazil                 
Altenhoff, W.        Max Planck Institut fur Radioastronomie, FRG             
Andersson, Ch.       Onsala Space Observatory, Sweden                         
Arnal, E.            Instituto Argentino de Radioastronomia, Argentina        
Bajaja, E.           Instituto Argentino de Radioastronomia, Argentina        
Batelaan, P.         Jet Propulsion Laboratory, USA                           
Batrla, W.           University of Illinois, USA                              
Baum, S.             University of Maryland, USA                              
Berulis, J.          Lebedev Physical Institute, USSR                         
Biggs, J.            University of Sydney, Australia                          
Bird, M.             Universitat Bonn, FRG                                    
Bockelee-Morvan, D.  Observatoire de Paris-Meudon, France                     
Boriakoff, V.        Cornell University, USA                                  
Botti, C.            Instituto de Pesquisas Espaciais, Brazil                 
Bourgeois, G.        Observatoire de Paris-Meudon, France                     
Bretas Filhd, F.     Instituto de Pesquisas Espaciais, Brazil                 
Butner, H.           University of Texas, USA                                 
Bystrova, N.         Special Astrophysical Observatory, USSR                  
Campbell, D.         National Astronomy and Ionosphere Center, Puerto Rico    
Cancoro, A.          Instituto de Pesquisas Espaciais, Brazil                 
Cersosimo, J.        Instituto Argentino de Radioastronomia, Argentina        
Claussen, M.         University of Massachusetts, USA                         
Cohen, J.            University of Manchester, UK                             
Colom, P.            Observatoire de Paris-Meudon, France                     
Colomb, F.           Instituto Argentino de Radioastronomia, Argentina        
Comoretto, G.        Osservatorio Astrofisico Arcetri, Italy                  
Cordes, J.           Cornell University, USA                                  
Crovisier, J.        Observatoire de Paris-Meudon, France                     
de Pater, I.         University of California, Berkeley, USA                  
Del Ciampo, L.       Instituto de Pesquisas Espaciais, Brazil                 
Despois, D.          Universite de Bordeaux, France                           
Destombes, J.        Universite de Lille, France                              
Duncan, R.           CSIRO Division of Radiophysics, Australia                
Ekelund, A.          Onsala Space Observatory, Sweden                         
Ekelund, L.          Onsala Space Observatory, Sweden                         
Encrenaz, P.         Observatoire de Paris-Meudon, France                     
Falchi, A.           Osservatorio Astrofisico Arcetri, Italy                  
Forster, R.          CSIRO Division of Radiophysics, Australia                
Forveille, T.        Universite de Grenoble, France                           
Frerking, M.         Jet Propulsion Laboratory, USA                           
Friehe, K.           Instituto de Pesquisas Espaciais, Brazil                 
Gagliardi, L.        Osservatorio Astrofisico Arcetri, Italy                  
Galt, J.             Dominion Radio Astrophysical Observatory, Canada         
Gaylard, M.          Hartebeesthoek Radio Astronomy Observatory, South Africa 
Gerard, E.           Observatoire de Paris-Meudon, France                     
Gossachinskij, I.    Special Astrophysical Observatory, USSR                  
Gulkis, S.           Jet Propulsion Laboratory, USA                           
Harmon, J.           National Astronomy and Ionosphere Center, Puerto Rico    
Haschick, A.         Haystack Observatory, USA                                
Hasegawa, T.         Nobeyama Radio Observatory, Japan                        
Hoban, S.            University of Maryland, USA                              
Huchtmeier, W.       Max Planck Institut fur Radioastronomie, FRG             
Irvine, W.           University of Massachusetts, USA                         
Judaeva, N.          Special Astrophysical Observatory, USSR                  
Kaifu, N.            Nobeyama Radio Observatory, Japan                        
Kaufmann, P.         Instituto de Pesquisas Espaciais, Brazil                 
Kinzel, W.           University of Massachusetts, USA                         
Kitamura, Y.         Nobeyama Radio Observatory, Japan                        
Klein, M.            Jet Propulsion Laboratory, USA                           
Krevsa, E.           Max Planck Institut fur Radioastronomie, FRG             
Kuiper, T.           Jet Propulsion Laboratory, USA                           
Lewis, M.            National Astronomy and Ionosphere Center, Puerto Rico    
Losovski, B.         Lebedev Physical Institute, USSR                         
Madden, S.           University of Massachusetts, USA                         
Malzoni, M.          Instituto de Pesquisas Espaciais, Brazil                 
Martin, C.           Instituto Argentino de Radioastronomia, Argentina        
Matthews, H.         Hertzberg Institute of Astrophysics, Canada              
Mazzaro, R.          Instituto Argentino de Radioastronomia, Argentina        
Melad, I.            Instituto de Pesquisas Espaciais, Brazil                 
Mirabel, I.          University of Puerto Rico, Puerto Rico                   
Montiero do Vale, J. Instituto de Pesquisas Espaciais, Brazil                 
Morras, R.           Instituto Argentino de Radioastronomia, Argentina        
Nelson, G.           CSIRO Division of Radiophysics, Australia                
Norris, R.           CSIRO Division of Radiophysics, Australia                
Ohishi, M.           Nobeyama Radio Observatory, Japan                        
Olalde, J.           Instituto Argentino de Radioastronomia, Argentina        
Palagi, F.           Osservatorio Astrofisico Arcetri, Italy                  
Palmer, P.           University of Chicago, USA                               
Persson, G.          Onsala Space Observatory, Sweden                         
Petroni, M.          Instituto de Pesquisas Espaciais, Brazil                 
Pickett, H.          Jet Propulsion Laboratory, USA                           
Poppel, W.           Instituto Argentino de Radioastronomia, Argentina        
Reynolds, J.         University of Sydney, Australia                          
Scalise, E.          Instituto de Pesquisas Espaciais, Brazil                 
Schaefer, M.         Jet Propulsion Laboratory, USA                           
Schloerb, P.         University of Massachusetts, USA                         
Schmidt, J.          Max Planck Institut fur Radioastronomie, FRG             
Schraml, J.          Max Planck Institut fur Radioastronomie, FRG             
Sestokas, B.         Instituto de Pesquisas Espaciais, Brazil                 
Shang, Q.            Yunnan Observatory, People's Republic of China           
Shapiro, I.          Harvard-Smithsonian Center for Astrophysics, USA         
Silva, A.            Instituto Argentino de Radioastronomia, Argentina        
Snyder, L.           University of Illinois, USA                              
Sorochenko, R.       Lebedev Physical Institute, USSR                         
Stumpff, P.          Max Planck Institut fur Radioastronomie, FRG             
Suzuki, H.           Nobeyama Radio Observatory, Japan                        
Swade, D.            University of Massachusetts, USA                         
Tateyama, C.         Instituto de Pesquisas Espaciais, Brazil                 
Terasranta, H.       Helsinki University of Technology, Finland               
Terzian, Y.          Cornell University, USA                                  
Thum, C.             Institut de Radioastronomie Millimetrique, Spain         
Tofani, G.           Osservatorio Astrofisico Arcetri, Italy                  
Tolmachev, A.        Lebedev Physical Institute, USSR                         
Turner, B.           National Radio Astronomy Observatory, USA                
Urpo, S.             Helsinki University of Technology, Finland               
Vilas Boas, J.       Instituto de Pesquisas Espaciais, Brazil                 
von Kap-Herr, A.     Max Planck Institut fur Radioastronomie, FRG             
Walmsley, M.         Max Planck Institut fur Radioastronomie, FRG             
Wang, J.             Yunnan Observatory, People's Republic of China           
Wannier, P.          Jet Propulsion Laboratory, USA                           
Webber, J.           Haystack Observatory, USA                                
Winnberg, A.         Onsala Space Observatory, Sweden                         
Wootten, A.          National Radio Astronomy Observatory, USA                
Zimmermann, P.       Universitat zu Koln, FRG                                 
Zinchenko, I.        Lebedev Physical Institute, USSR                         
_____________________________________________________________________________ 
                                                                              
                                                                              
8. ACKNOWLEDGEMENTS                                                           
                                                                              
     F. P. Schloerb and W. M. Irvine, as leaders of the radio astronomy       
effort, have been aided in their effort by a number of students, post-docs and
secretaries at the University of Massachusetts during the course of our       
involvement with the IHW.  We gratefully acknowledge the efforts of R.        
Bassett, M. Claussen, C. Clemens, R. Molloy, G. Moriarty-Schieven, D. Swade,  
and L. Tacconi-Garman, who have provided assistance to the project at various 
times throughout its duration.                                                
                                                                              
     As leaders of the Radio Science effort, Schloerb and Irvine would also   
like to acknowledge especially two of the other members of the Discipline     
Specialist Team listed in Table I.  W. M. Kinzel, the manager of the Radio    
Science Archive,  has made a substantial and noteworthy contribution of time  
and effort to the actual archiving of the data while serving as a graduate    
student at the University of Massachusetts.  The archive that exists today    
would have been impossible to complete without his participation in the       
project.  Finally, we would like to thank particularly our Co-Discipline      
Specialist E. Gerard for his continued leadership in the field of cometary    
radio astronomy, his enthusiastic support of the International Halley Watch,  
and his efforts on our behalf.                                                
                                                                              
                                      F. Peter Schloerb and William M. Irvine 
                                      Discipline Specialists for Radio Science
                                      Five College Radio Astronomy Observatory
                                      Department of Physics and Astronomy     
                                      University of Massachusetts             
                                      Amherst, MA 01003