***** File PDS_IHW.TXT PDS LABELS The International Halley Watch agreed early in the project that all data would be submitted from the individual Disciplines to the Lead Center using the FITS format (Wells et al., 1981). When the decision was made to distribute this information on CD-ROM, it was determined that the data had to have even broader accessibility. For this reason the original FITS files, with contiguous headers and data, were split into separate files distinguishable by their filename extensions (.HDR for headers). The file sizes were preserved as multiples of 2880 bytes, allowing the original FITS byte stream to be recovered by concatenating the appropriate header and datafile. In addition, detached (PDS) labels were constructed to allow parallel definition of the data files for the Planetary Data System (PDS). The SPIDS (Standards for the Preparation and Interchange of Data Sets, Martin, T. Z., et al, Document D-4683, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA) document version 1.1 was the primary reference to Bthe Object Description Language (ODL) necessary to create the PDS labels. (We acknowledge R. Borgen and M. Martin, PDS- JPL, for assisting the IHW through version 2.0 of the ODL that allows for description of HEADER, TEXT, and SPECTRUM.) There are five fundamental data objects in this archive: IMAGE, TABLE, TEXT, HEADER, and SPECTRUM. Our aim was to construct a basic PDS label for each data file on the CD-ROM. These PDS labels contain pointers to the actual data files (or to headers describing data submitted to the archive). There has been no effort to duplicate the documentation contained in the full FITS headers because the PDS and FITS headers for a given data file differ only in the filename extension. Instead we have attempted to use the power of the PDS label syntax to fully describe the data structures and thus gain access to the powerful software already supported by that group. A more full explanation of each object is carried in text (.TXT) files HDRFORM, IMAGFORM, SPECFORM, TABLFORM, and TEXTFORM. In addition, a further description of the PDS detached label is listed in file LBLFORM.TXT. Each of these files was used as a reference for the SFDU pointers in the VOLDESC.SFD. Most keywords were already in the Planetary Science Data Dictionary but a few dealing with the spectral_image_qube were introduced to specifically describe the IHW data. A listing of these keywrods with definitions follow. Keyword Definitions The definitions of the keywords used in the detached PDS labels on the International Halley Watch Arcive CD-ROMs are given below. Where applicable the definitions are taken from the draft PSDD (Planetary Science Data Dictionary 1990) or the PDS Standards for the Preparation and Interchange of Data Sets (SPIDS) document (Martin et al., 1988). There are some differences from the PDS data dictionary in the definitions used on this CD-ROM, since the definitions of some keywords in the current PDS data dictionary do not dBescribe comet data. In addition, some keywords for processed (UVFITS) data do not exist in the current PDS data dictionary. B AXES The number of independent variables in a data array. BAND_STORAGE_TYPE The arrangement of data in a qube ordered by spectral bands. BYTES The number of bytes containing a data item. COLUMNS The number of items of information in each row of a data table. CORE_DESCRIPTION The dependent variable expressed in a spectral_image_qube. CORE_ITEMS The number of elements along an independent axis. CORE_NAME Identifying name for avariable along an independent axis. DATA_SET_ID A unique alphanumeric identifier for a data set. It is used as a primary key in the PDS catalog. DATA_SET_PARAMETER_NAME The name of the physical parameter represented in an image. Note this definition differs from the PDS data dictionary definition. DATA_TYPE The data type of a data item. Valid values are INTEGER, REAL, DATE, TIME, and CHARACTER. DERIVED_MAXIMUM The maximum value held in a data record. DERIVED_MINIMUM The minimum value held in a data record. DESCRIPTION Text describing an object. Sometimes this is expressed as a pointer to another file containing the descriptive text; e.g., FITS header. ENCODING_TYPE Previous pixel compression of 16-bit data; also called first difference. END_OBJECT This keyword is used by ODL to indicate the end of a data object definition. FILE_RECORDS The number of physical records in a data file. FORMAT B The Fortran 77 representation of the format statement needed to read a data item. IMAGE The data in an image file, expressed as a pointer to the record where the data begins. For example, ^IMAGE = ("filename",3) indicates that image data begins in record 3 of file "filename". INTERCHANGE_FORMAT The type of data stored in a data table, such as ASCII or BINARY. ITEMS Elements held in any arbitrary variable. ITEM_BITS Number of bits per item. ITEM_TYPE The data type of an item. LINES The number of lines in an image. LINE_SAMPLES The number of samples contained in each image line. B MINIMUM_SAMPLING_PARAMETER For the spectrum object, the first value along the fastest varying axis. NAME The name of a column in a table. NOTE Descriptive text about a data file, referring to IHW disciplines. OBJECT This keyword specifies the name of a data object. It is used by ODL to indicate the start of a data object definition. OBSERVATION_TIME A timBe associated with the midpoint of the International Halley Watch set of observations. OBSERVATION_ID A unique number held to identify each archived measurement gathered by the International Halley Watch. OFFSET A shift in zero point required to properly calculated the reduced value represented in a FITS data record. PRODUCER_FULL_NAME The full name of those mainly responsible for production of a data set. RECORDS The number of records in the object being described; for example, the number of records in a header object. RECORD_BYTES The number of bytes in each record of a data file. RECORD_TYPE The record structure type of a data file. Valid values are FIXED_LENGTH, VARIABLE_LENGTH, and STREAM. Images and data tables usually have fixed-length records, whereas text files have stream format records. ROWS The number of logical records in a data table. ROW_BYTES The number of bytes in each row (i.e., logical record) of a data table. SAMPLE_BITS The number of bits of data comprising one sample or pixel in an image or element in other objects. SAMPLE_TYPE The data type of an image sample or pixel. The table below lists the values used on this CD-ROM: UNSIGNED_INTEGER An unsigned integer value. Samples with a length of 16 bits are in most-significant-byte first order. MSB_INTEGER A signed integer with most-significant-byte leading as required by FITS format. COMPLEX_INTEGER The value represented in a process step (UVFITS) for certain types of radio data. SAMPLING_PARAMETER_DESCRIPTION Text explanation of independent variable. SAMPLING_PARAMETER_INTERVAL Smallest uniform change of independent variable. SAMPLING_PARAMETER_ITEMS Number of elements along independent axis. SAMPLING_PARAMETER_NAME Name associated with independent variable. SAMPLING_PARAMETER_UNIT Unit associated with independent variable. SCALING_FACTOR The factor that must be applied to the FITS data record to scale the values as described by UNIT. START_BYTE The byte position of the beginning of a data item within a row of data. START_TIME The date and time of the beginning of an event, such as data collection, in PDS standard (UTC) format. TARGET_NAME The name of a planetary body, such as a planet or satellite. TYPE The type of header in a data file, such as a VICAR2 label embedded in the image file. UNIT The units of measure of a data item. REFERENCES Martin, T.Z., Martin, M.D., Davis, R.L., Mehlman, R., Braun, M., Johnson M.: October 3, 1988, Standards for the Preparation and Interchange of Data Sets, Version 1.1, JPL D-4683. Wells, D.C., Greisen, E.W., and Harten, R.H.: 1981, Astron. Astrophys. Suppl. Ser. 44, 363.