PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "2004-01-13; J. Diaz del Rio (ESA). v1.0" RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 1994-12-31 NOTE = "Description of contents in the EXTRAS subdirectory." END_OBJECT = TEXT END ***** File EXTRINFO.TXT Contents of the EXTRAS Directory This file describes the content of the EXTRAS directory and the files are listed below: EXTRAS.TXT - This file describing contents PIA000xx.HDR - Heather of the FITS file xx (from 01 to 41) containing the information about the data in the file PIA000xx.TBL. PIA000xx.TBL - Data in FITS format, without heather. These data corresponds with the heather PIA000xx.HDR (from 01 to 41) and along with it corresponds with the original FITS file named PIA000xx.FIT. Original the data were in FITS format, but they were split into two files as shown in the description above. Formating and Explanatory Notes of the original FITS files Original Format The data for these files were received as a series of FITS files, each of which consisted of spectra of a single mode. Amplitude-triggered samples in the spectra were indicated by an "X" following the sample. Reformatting at SBN The following changes were made to the data: o A program was written to parse the headers and spectra and convert the ASCII values to binary form. Parameter values were ordered to facilitate comparison between the MPI and IKI submissions for the VEGA missions, which used the same instrument (PUMA). o Flagged amplitudes, followed by an "X" in the text file, were indicated in the binary file as a additional byte set equal to 1 for flagged amplitudes, 0 otherwise. This is the same system used for the IKI VEGA submissions. o All spectra of the same mode were collected into a single, fixed- length table. o The original order of the spectra in the FITS files, as well as the order of the text files themselves, was preserved in the combined mode tables. This order was assumed to be chronological. Known Anomalies/Problems: o Little or no explanation was available for some of the parameters in the spectrum headers. This is indicated in the DESCRIPTION part of the PDS label for these datasets. o It has not yet been possible to translate the times in this file, which are apparently in units of spacecraft clock time, to UT. o In the received FITS file numbered 40, the final spectrum in the file (sequence number 2991, event number 46698, time 48110) was truncated. It is not clear if only this last spectrum was lost or if other spectra might have followed since the NAXIS1 and NAXIS2 values from the header indicate more data. The incomplete spectrum was omitted entirely from the binary table. o Two mode 1 spectra were found which contained an odd number of bytes in the spectrum. In mode 1 the number of bytes should be even, as each sample in the spectrum consists of a time sample byte and an amplitude sample byte. In these cases the single byte was assumed to be a time value and a null amplitude byte was appended to the spectru . o In working with these files it was noted that many spectra exhibited strange features, including: - parameter values but no spectrum bytes (i.e., zero-length spectra) - repeating time values of 255 (the maximum possible time) - repeating amplitude values of 127 (the maximum possible) - repeating values of 32 (ASCII code for blank) o There was a failure in the instrument during the fly-by. The following is taken directly from the FITS file header which was attached to the text files: "During the actual flyby two out of six multiplier-amplifiers failed, yielding incorrect amplitude information in the mass spectra channel; to obtain partial correction for amplitude, use F(a), where F(0) = 0 F(20) = 49 F(1...4) = a*2 + 21 F(21) = 52 F(5...8) = a + 25 F(22) = 57 F(9...14) = a + 26 F(23...25) = 3*(a-23) + 62 F(15,16) = a + 27 F(26...83) = a + 4a F(17...19) = a + 2b F(84...127) = 128 NOTE: Despite this correction the amplitude ranges 1...22 and around 51...65 are incomplete." No further documentation of this problem was available. Specifi- cally, it seems likely the "2b" in the equation for F(17...19) was intended to be "28". Notes about the FITS format used in these data All data were submitted to the International Halley Watch Lead Center on magnetic tape, written in FITS or ascii format. There are three primary references to basic FITS (Wells et al, 1981) and its extensions (Greisen and Harten, 1981, Harten et al, 1988). Although commonly viewed as a magnetic tape format, the actual FITS specifications can be interpreted to describe a general byte stream. As such, FITS files may be written on any storage medium, including CD-ROM. Note that there is no inherent record structure called for in the FITS agreements, only a blocking structure for block oriented media such as magnetic tape. The basic FITS agreements call for only a few required keywords (SIMPLE, BITPIX, NAXIS, END must be present; EXTEND may appear; keywords NAXIS1, ..., NAXISn appear as defined by the value of NAXIS). We have also followed recommended conventions for the representation of values of keywords (dates in the format 'dd/mm/yy', SI units used where possible, etc.). The IHW has defined an additional set of mandatory keywords for all submissions to the Lead Center. These are presented in the table below: OBJECT - Name of the object in the data file, a text string. FILE-NUM - Unique 6-digit number of the file submitted to the Lead Center. The first digit identifies the discipline, the other digits are assigned by the individual Disciplines, but must uniquely identify the file. DATE-OBS - UT Date of mid-observation, in the format 'dd/mm/yy'. TIME-OBS - UT Time of mid-observation, as fractional day. DATE-REL - IHW internal release date for data, as date string. DISCIPLN - Name of the network submitting the file, a text string. LONG-OBS - Longitude of the submitting observatory, in the format 'ddd/mm/ss', with degrees from 0 to 360, increasing in the eastward sense. LAT--OBS - Latitude of the submitting observatory, in the format 'sdd/mm/ss'. SYSTEM - An 8-digit coded character string identifying the Discipline, observatory and instrument which supplied the data. The first character identifies the network, the next three identify the observatory (by IAU code number, where one is assigned, 500 otherwise). The next four digits either identify the telescope/instrument combination (if there is an IAU number for the observatory) or the country and observatory (if no IAU number). OBSERVER - Name of the observer(s) who took the data, a text string. The notation "ET AL." indicates that there were more than two observers, and the names of the additional observers are given in a COMMENT later in the header, with the subkeyword "ADD. OBS." SUBMITTR - Name of the person submitting the data to the Lead Center, a text string. SPEC-EVT - A logical value indicating that the observation is a special event. Either T or F. DAT-FORM - A character string defining the form of the data, e.g., 'ASCII', 'NODATA'. REFERENCES Greisen, E. W. and Harten, R. H.: 1981, Astron. Astrophys. Suppl. Ser. 44, 371. Harten, R. H., Grosbol, P., Greisen, E. W. and Wells, D. C.: 1988, Astron. Astrophys. Suppl. Ser. 73, 365. Wells, D. C., Greisen, E. W. and Harten, R. H.: 1981, Astron. Astrophys. Suppl. Ser. 44, 363.