PDS_VERSION_ID = PDS3 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 80 OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 1999-09-29 NOTE = "N/A" END_OBJECT = TEXT END Voyager Radio Science Archive Titan Open-Loop Raw Data (VG1-SSA-RSS-1-ROCC-V1.0) AAREADME.TXT 29 September 1999 R.A. Simpson Stanford University ============================================================================== INTRODUCTION ============================================================================== This compact disc contains archival raw, partially processed, and ancillary/supporting data acquired during the Voyager 1 (VG1) radio occultation by Titan. Observations were carried out using the VG1 spacecraft and Earth-based receiving stations of the NASA Deep Space Network (DSN). The observations were designed so that physical structure of Titan's atmosphere (including surface temperature and pressure) could be determined. The data also allowed estimation of Titan's radius and a marginal detection of an ionosphere. The spacecraft S- and X-band carrier signals served as coherent signal sources, probing the atmosphere at various depths. Output from the DSN receivers was sampled and recorded for later analysis. Two recording systems were used, running in parallel with staggered start/stop times. The original data tapes were converted to computer-compatible tapes (CCTs) later at the NASA Jet Propulsion Laboratory. The data from these CCTs (with names of the form VJnnnn) represent the primary archival product here. Each disc in the volume set contains data from part of the Titan occultation period. Data from successive discs are in chronological order, except that data from different recorders are not mixed on a single CD. A table of contents is included with each volume, listing each data file in the volume; a separate table of contents shows all files within the data set. The table below lists the individual volumes (CDs) and (very briefly) their respective contents. VOLUME_ID Start Time (1980/317) Recorder S-Band Tapes X-Band Tapes --------- --------------------- -------- ------------- ------------- VG_2301 06:35:00 - 06:53:20 A VJ6281-VJ6284 VJ6292-VJ6303 VG_2302 06:55:00 - 07:13:20 A VJ6285-VJ6288 VJ6304-VJ6315 VG_2303 07:15:00 - 07:28:20 A VJ6289-VJ6291 VJ6316-VJ6324 VG_2304 07:25:00 - 07:48:20 B VJ6361-VJ6365 VJ6366-VJ6380 VG_2305 07:45:00 - 08:08:20 A VJ6325-VJ6329 VJ6334-VJ6348 VG_2306 08:10:00 - 08:28:20 A VJ6330-VJ6333 VJ6349-VJ6360 VG_2307 23:01:40 - 23:13:20 A VJ6589-VJ6591 VJ6595-VJ6602 VG_2308 23:15:00 - 23:28:20 A VJ6592-VJ6594 VJ6603-VJ6611 The last two volumes contain data collected after the Titan experiments and may be useful in characterizing (calibrating) the data acquisition system. The Voyager Radio Science Team preferred consistency checks within the Titan data and did not use the calibration tapes extensively. ============================================================================== VOLUME SET INFORMATION ============================================================================== This disc is one of several which contain raw data from the Voyager 1 Titan radio occultation. Each archive volume has the structure illustrated in the diagram below -- except that the DOCUMENT directory, because of its size, appears in full only on the final volume. The primary data files for these volumes are the Original Data Records (ODRs), stored in the ODR directory. Each ODR appears on only one volume in the data set. Snapshots of each ODR are included in the BROWSE directory. The primary data files are accompanied by a number of ancillary files. These include receiver frequency files in the CALIB directory, ephemerides and High-Gain Antenna (HGA) pointing files in the GEOMETRY directory, and documents and other descriptive material in the CATALOG and DOCUMENT directories. With the exception of the DOCUMENT directory, which appears in full on only the final volume, these ancillary directories and files are repeated on each volume. The root of each disc includes a general description of the data set (this file, named AAREADME.TXT), a cumulative file of errors and comments (ERRATA.TXT), and a brief description of the volume. Minor errors will be documented in succeeding versions of the ERRATA.TXT file, and updated versions of documentation and ancillary files will appear on succeeding volumes. A user concerned about having the most recent version of these files should obtain them from the last volume in the data set. The diagram below shows the organization of each volume, starting from the root of the compact disc (detached PDS labels are not shown). root | |- AAREADME.TXT |- ERRATA.TXT |- VOLDESC.CAT | |- CALIB | | | |- CALINFO.TXT Overview of directory | |- VG1TPOC1.DAT Binary POCA file | `- VG1TPOC2.TAB ASCII POCA data | |- CATALOG | | | |- CATINFO.TXT Streamlined PDS catalog files | |- MISSION.CAT for mission, host, instrument, | |- INSTHOST.CAT data set, personnel, references, | |- INST.CAT and target | |- DATASET.CAT | |- PERSON.CAT | |- REF.CAT | `- TARGET.CAT | |- DOCUMENT (full directory is included only on the final volume; | | an asterisk * identifies files appearing on | | all volumes) | | | |- DOCINFO.TXT Overview of directory (*) | |- CRS80SIS.TXT SIS for original CRS files | |- CRSTAPES.TXT Modern description of CRS data | |- MBODRPRC.TXT Processing schedule for MBODR data | |- OP1S_TXT.LBL Label for VG1 RS Operations Plan | |- OP1S_TXT.ASC Text of VG1 RS Operations Plan | |- OP1SF201.PS Fig 2-1 in VG1 RS Operations Plan | |- ... other Ops Plan figures | |- RSC_11_5.TXT SIS for original POCA file (*) | |- RSC_11_6.TXT SIS for raw radio data (*) | |- TAPELIST.TXT Description of tape numbering | |- TCI10TXT.LBL Label for DSN 64-m subnet description | |- TCI10TXT.ASC Text of DSN 64-m subnet description | |- TCI10_F1.PS Fig 1 of DSN 64-m subnet description | |- TCI10_F2.PS Fig 2 of DSN 64-m subnet description | |- TIMELINE.TXT Significant events of Titan encounter | |- TK_FTP.TXT NAIF access information (*) | |- TK_DESCR.TXT NAIF Toolkit description (*) | |- TK_INSTL.TXT NAIF Toolkit installation (*) | `- USOFREQS.TXT Summarizes USO frequency knowledge | |- GEOMETRY | | | |- GEOMINFO.TXT Overview of directory | |- CRS009AA.CRS CRS file for VG1 at Titan | |- VG1_SAT.SPK NAIF SPK file for Titan/Saturn | |- VH009.DAT HGA pointing data (binary) | `- VH009T.TAB HGA pointing data (ASCII) | |- INDEX | | | |- INDXINFO.TXT Overview of directory | |- INDEX.TAB List of data file contents, this volume | `- CUMINDEX.TAB List of data file contents, all volumes | |- SOFTWARE | | | |- SOFTINFO.TXT Overview of directory | |- CRS2ASC.F Converts binary to ASCII CRS file | |- CRS2LBL.F Extracts label info from ASCII CRS | |- DOY_MMDD.F Day/month conversion subroutine | |- DTCVT.F Subroutine normalizes date/time | |- GET_BITS.F Extracts bits from array of 32-bit ints | |- GET_HDR.F Unpacks RSC-11-6 header to array | |- MAKEFILE.CMD Unix Makefile for directory | |- PREP_11_6.F Converts RSC-11-6 data to standard format | |- PRT_HDR0.F Prints single RSC-11-6 header | |- PRT_HDR1.F Prints single RSC-11-6 header | |- RDHDR.F Gets RSC-11-6 record, lists header | |- SLIP.F Gets number of slipped samples | |- UNI2ASC.F Univac character to ASCII converter | |- UNI2DP.F Univac to double precision converter | |- UNI2INT.F Univac to integer converter | |- UNPK.F Unpacks RSC-11-6 data file | `- XFR_11_6.F Unpacks 8-bit data to 16-bit fields | |- ODR | |- VJnnnnCC.ODR Data file | |- ... more data files | `- BROWSE |- VJnnnnCC.PS Snapshot of VJnnnnCC.ODR data |_ ... more snapshots (PostScript format) ============================================================================== ERRATA ============================================================================== A cumulative list of errors and changes is maintained in the file ERRATA.TXT at the root level of each volume. ERRATA.TXT in higher numbered volumes (or higher version numbers) will have errors for earlier volumes. ============================================================================== DISC FORMAT ============================================================================== The disc is organized according to the PDS standard for "one data set, many volumes." This file (AAREADME.TXT), a PDS volume object definition (VOLDESC.CAT), and the listing of errors and changes (ERRATA.TXT) are included at the root level. The following directories of descriptive material are also at the root level: CALIB contains files of receiver tuning data CATALOG contains descriptive files for cataloging the data DOCUMENT contains software interface specifications for primary and ancillary data, a copy of the Radio Science Operations Plan, descriptions of DSN equipment, instructions on how to obtain and use the NAIF Toolkit, and documentation on file naming and organization. Because of its size, the full DOCUMENT directory appears only on the final volume; on the other volumes only the SISs needed to understand binary files (RSC_11_5.TXT, RSC_11_6.TXT, TK_FTP.TXT, TK_DESCR.TXT, and TK_INSTLL.TXT) appear. GEOMETRY contains ephemerides and high-gain antenna pointing data INDEX contains index information on each of the data files included in this disc; it also includes a cumulative index to all files in this data set. The remaining directories at the root level contain data files and detached PDS labels. ODR contains the raw data files BROWSE contains snapshots of each data file (each snapshot is a four-panel plot including a histogram, power vs time plot of data samples, time-ordered power spectra derived from samples, and an extract from the PDS label) ============================================================================== FILE FORMAT ============================================================================== Catalog Files ------------- Files with names ending in *.CAT are catalog files; they are found in the CATALOG directory, and VOLDESC.CAT is in the root of the CD. Each is an ASCII file comprising a few keyword-label pairs and one or more object definitions. Each file in the CATALOG directory is an ASCII file with fixed-length records of 72 characters; each record ends with an ASCII carriage-return line-feed pair in positions 71 and 72. The VOLDESC.CAT file has 80 character records with the carriage-return line-feed pair in positions 79 and 80. Text Files ---------- Files with names ending in *.TXT are text files and have attached PDS labels; they are found in most directories and in the root of the CD. The attached label includes a few keyword-value pairs and a brief TEXT object definition. The attached label and TEXT object have fixed-length records of 80 characters each. Each record contains only ASCII printable characters except for an ASCII carriage-return line-feed pair in positions 79 and 80. Detached Labels --------------- All other files (except in the SOFTWARE directory) have detached PDS labels. A detached PDS label is a file in its own right; its name is the same as its associated data file except that it ends with the extension *.LBL. Detached labels are ASCII files with 80 character records; each record ends with an ASCII carriage-return line-feed pair. Documents --------- Documents are found only in the DOCUMENT directory; each is defined by a combined detached label. In addition to having an associated data file (the document body) the combined detached label also defines links to files containing figures in PostScript format. The body of the document is an ASCII file with variable length records. Each record is delimited by an ASCII carriage-return line-feed pair. The text file name ends with the extension *.ASC. Each figure is contained in a separate PostScript file having a name ending with the extension *.PS. The first few characters of the file name match the first few characters in the name of the body/label files. The PostScript files have records of variable lengths; each record is delimited by an ASCII carriage-return line-feed pair. Browse Files ------------ Browse files are PostScript files of single-page four-panel plots; they are found only in the BROWSE directory. File names are of the form VJnnnnCC.PS (to match the corresponding ODR file). The PostScript files have records of variable lengths; each record is delimited by an ASCII carriage-return line-feed pair. SPK files --------- SPK files are stored in NAIF transfer format. They have file names ending with the extension *.SPK and appear only in the GEOMETRY directory. SPK files are ASCII files of variable length records, each delimited by an ASCII carriage-return line-feed pair. It may be necessary to convert the delimiter to the local default delimiter before using the archival file with NAIF software. Tables ------ Tables are stored in ASCII files with fixed length physical records. They have file names ending with the extension *.TAB and appear in the CALIB, GEOMETRY, and INDEX directories. File CRS009AA.CRS in the GEOMETRY directory is also a table. Table files can actually contain more than one table; and the logical record lengths of the tables can be different, so long as they are commensurate with the physical record length. The logical records in a single table are all the same, and each ends with an ASCII carriage-return line-feed pair. Details of the table file structure are specified in the associated PDS label. Software -------- Software is stored in ASCII files in the SOFTWARE directory (only). File names end with extensions *.F (FORTRAN 77 code) or *.CMD (Unix makefile). Files have records with variable lengths, each record being delimited by an ASCII carriage-return line-feed pair. Software files do not have PDS labels; but the SOFTINFO.TXT file provides a terse description of the main programs, and each routine has in-line comments. ============================================================================== USER SUGGESTIONS ============================================================================== Users may have different objectives when approaching this data set. But an example may help show how the various files can be used to achieve a modest goal. If the user is interested in reprocessing the Titan ingress occultation, the following steps would be appropriate: 1. Consult TIMELINE.TXT in the DOCUMENT directory to determine the approximate time of the ingress occultation (07:11-07:15). 2. Use TAPELIST.TXT (also in the DOCUMENT directory) to identify the relevant tapes (VJ6288 for S-band and VJ6313-VJ6315 for X-band; minimum set). 3. Write a program using the NAIF Toolkit, the VG1_SAT.SPK ephemeris file, and the VH009T.TAB antenna pointing file to reconstruct the observing geometry. Include light-time corrections. The data files are in the GEOMETRY directory. 4. Add Doppler calculations to the program so that the frequency of the carrier can be predicted at both S- and X-band. The USO X-band carrier frequency is given in USOFREQS.TXT in the DOCUMENT directory. The receiving system is outlined in CATALOG/INST.CAT and described in more detail in DOCUMENT/OP1S_TXT.LBL. Ground receiver tuning was controlled by the POCA (see VG1POC2.TAB in the CALIB directory). General relativistic corrections for the gravitational fields of the Sun, Earth, and Saturn may improve the result. 5. Write a program to calculate the frequency/phase of the observed carrier in the receiver baseband output (the VJnnnn data found in step 2). The ODR format is documented in RSC_11_6.TXT in the DOCUMENT directory. The unpacking program UNPK.F in the SOFTWARE directory may be useful; PREP_11_6.F could serve as a model for early stage processing. Attention should be paid to data drop-outs and lost records (or fragmented files), if any (see CATALOG/DATASET.CAT and DOCUMENT/TAPELIST.TXT). 6. The effects of the atmosphere will be represented by the phase of the observed signal compared with the phase of the predicted signal calculated (step 4) in the absence of an atmosphere. ============================================================================== ACKNOWLEDGMENTS ============================================================================== These data were collected under auspices of the Voyager Project. Von R. Eshleman and G. Leonard Tyler of Stanford University were the Radio Science Team Leaders. David P. Hinson and Essam A. Marouf were involved in creating and validating the archive. At PDS the assistance of Ron Joyner and Lyle Huber was appreciated. ============================================================================== DISCLAIMER ============================================================================== Although considerable care has gone into making this volume set, errors are both possible and likely. Users of the data are advised to exercise the same caution as they would when dealing with any other unknown data set. Reports of errors or difficulties would be appreciated. Please contact one of the persons listed below. ============================================================================== COGNIZANT PERSONNEL ============================================================================== The person most directly responsible for construction and release of this volume set is Dick Simpson, Experiment Engineer for the Mars Global Surveyor Radio Science Team and Radio Science Advisor to the Planetary Data System. Although many people contributed to the volume set, any faults in the product are his alone. Richard A. Simpson Center for Radar Astronomy Packard Bldg - Room 332 Stanford University Stanford, CA 94305-9515 Tel: 650-723-3525 FAX: 650-723-9251 rsimpson@magellan.stanford.edu G. Leonard Tyler Center for Radar Astronomy Packard Bldg - Room 331 Stanford University Stanford, CA 94305-9515 Tel: 650-723-3535 FAX: 650-723-9251 len@nova.stanford.edu ============================================================================== ACRONYMS AND ABBREVIATIONS ============================================================================== CALIB Calibration (file and/or directory) CCT Computer Compatible Tape CD Compact Disc CR Carriage-Return (ASCII character) CRS Celestial Reference Set (format or file) DOY Day of Year DSN Deep Space Network HGA High Gain Antenna (device and/or file and/or directory) LF Line-Feed (ASCII character) MBODR Medium-Band Original Data Record NAIF Navigation and Ancillary Information Facility NASA National Aeronautics and Space Administration ODR Original Data Record (file and/or directory) PDS Planetary Data System POCA Programmable Oscillator Control Assembly RS Radio science SPK Spacecraft and Planet Kernel (file and/or directory) VG1 Voyager 1