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NASA Space Science Data Coordinated Archive Header



Availability: Archived at NSSDC, accessible from elsewhere

Time span: 1981-08-25 to 1981-08-26


This description was generated automatically using input from the Planetary Data System.

Data Set Overview ================ This data set consists of raw data collected during the Saturn radio occultation of Voyager 2 on 26 August 1981, ring scattering data collected during the same time period, test and calibration data collected about 8 hours earlier, and ancillary files that might be useful in analysis of those data. The raw data are sampled voltage outputs from receivers tuned to the Voyager carrier frequencies at both S-band and X-band during the occultation. The data have been reduced to give profiles of temperature and pressure as a function of height in the atmosphere [LINDALETAL1985] and to infer magnetic field orientations in the upper ionosphere [HINSON1984]. During the Saturn occultation, the Voyager 2 spacecraft provided a coherent, dual-frequency microwave radio signal source. The signal frequency was derived from a precision, onboard Ultra-Stable Oscillator (USO). The spacecraft high-gain antenna (HGA) beamed that signal through the atmosphere and rings of Saturn. As the spacecraft moved on its trajectory, the radio signal probed the atmosphere and rings at different radial positions from the center of mass. An hour later the signals were received using a 64-meter antenna of the NASA Deep Space Network (DSN) near Canberra (Australia). To keep the refracted radio beam aimed toward the DSN antenna during the atmospheric occultation, the spacecraft attitude was adjusted so that the high-gain antenna (HGA) was pointed at the virtual image of Earth on Saturn's limb. This ensured that maximum signal strength would be available from the deepest probing. During the deepest part of the atmospheric occultation, the HGA was pointed toward the rings to determine whether signals forward scattered by the ring particles could be detected on Earth. Related data sets of possible interest include: DATA_SET_ID Description ----------------------- -------------------------------VG1-SSA-RSS-1-ROCC-V1.0 Titan radio occultation raw data VG1-S-RSS-1-REDR-V1.0* Saturn Voyager 1 ingress radio occultation raw data VG1-S-RSS-1-ROCC-V1.0 Saturn Voyager 1 egress radio occultation and ring scattering raw data *tentative DATA_SET_ID assignment Parameters ========== The output of each S-band receiver was a sinusoidal carrier signal embedded in noise -- a voltage with bandwidth approximately 50 kHz and sampled at 300000 samples per second. The X-band receiver output was similar; but, because of greater potential for Doppler drift and prediction uncertainty, its bandwidth was 150 kHz and sampling rate was 300000 samples per second. Voltages typically were in the range +/- 10 volts; but the absolute levels were not calibrated. In fact, they are generally not needed since it is the frequency (or phase) of the signal (rather than amplitude) that is most useful in inferring properties of a neutral atmosphere or ionosphere, and amplitude calibration for ring observations can be obtained by referencing signals to the background radiothermal noise in the data stream. The frequency of the USO was known from monitoring during the Jupiter-Saturn cruise (and from post-Saturn observations). Doppler contributions from motions of the spacecraft, Earth, Saturn, and other bodies of the solar system were determined jointly with the Voyager Navigation Team. Relativistic Doppler contributions could be estimated from proximity to large masses. Receiver tuning was recorded in POCA (Programmable Oscillator Control Assembly) files, which are included with this archive. Processing ========== No processing per se has been carried out on these data. However, because of the high sampling rate, the 8-bit samples were recorded originally on wide-bandwidth analog video tape. The analog tapes were then replayed later at slower speeds and the digital data were extracted onto computer compatible tapes (CCTs) with each receiver channel on a separate set of tapes. Because the S-band data had been oversampled originally (300 ksps for a 50 kHz bandwidth), only one of every three samples was saved during the transfer of S-band data to CCTs. This process, known as 'decimation', meant that 300 seconds of data could be stored on an S-band CCT whereas only 100 seconds of X-band data would fit. Because analog recording technology was required to save the high data rate digital samples, there are occasional dropouts in the sample stream. These can be detected by paying special attention to counter fields in data record headers. Two analog recorders (A and B) were available at each DSN complex. Because a single recorder could not capture the entire set of Saturn occultation activities, the two were run in parallel with staggered start/stop times. Most data were collected using Recorder A; but Recorder B was used to capture the samples while Recorder A was being reloaded. Data ==== Primary data were delivered to Voyager Radio Science Team members in the form of 30 megabyte (MB) CCTs covering 300 s (S-band) or 100 s (X-band). Each tape had 6000 records of 5056 bytes (56 bytes of header information and 5000 8-bit samples of receiver output voltage). Tapes were numbered sequentially as CCTs were generated from the high density video originals. Tapes with Saturn data from Recorders A and B were numbered as follows: 1981-08-26 UTC Tape Numbers Recorder ----------------- ------------- -------03:45:00-04:20:00 C0BP01-C0BP21 B 04:15:00-04:55:00 C1BP01-C1BP24 A 04:50:00-05:40:00 C2BP01-C2BP30 B 05:10:00-06:05:00 C3BP01-C3BP30 A 06:15:00-07:05:00 C4BP01-C4BP30 B 06:20:00-07:15:00 C5BP01-C5BP33 A 07:15:00-07:40:00 C6BP01-C6BP15 B 07:20:00-08:00:00 C7BP01-C7BP24 A Test and calibration data were collected before the Saturn encounter on Recorder A (tapes C8BP01-C8BP19) and Recorder B (tapes C9BP01-C9BP19). 'B' in the tape names stands for the frequency band (S or X); 'P' stands for the circular polarization (L or R). Not all band/polarization combinations were collected at any given time. The original tape numbering has been preserved in the current file names, which have the form CnBPmmZZ.ODR. On tapes where one or more records could not be read, the original has been separated into two or more files. The character 'Z' indicates the ordering of these file fragments with 'A' being first (and the default with no tape reading errors), 'B' next, etc. Each Original Data Record (ODR) file is accompanied by a minimal PDS label briefly describing the contents and referring the user to detailed documentation on file format. The label file has name CnBPmmZZ.LBL. Ancillary Data ============== Geometry Data - The raw radio data were originally reduced by the Voyager Radio Science Team using ephemerides in Celestial Reference Set (CRS) format -- state vectors at regular intervals. The Saturn CRS file has been converted to ASCII and is archived as file CRS32_1A.CRS in the GEOMETRY directory. The current version of the NAIF SPK file for the Voyager Saturn encounter is also provided; it is in the NAIF 'transfer' format and is archived under the name VG2_SAT.SPK in the GEOMETRY directory. HGA Pointing Data - High-Gain Antenna (HGA) pointing information was delivered to the Voyager Radio Science Team as binary files on computer tape. Two original binary files and an equal number of ASCII translations are included in the GEOMETRY directory. File VU005.DAT and its ASCII translation VU005T.TAB are assumed to be the best files for analysis, but only because of the apparently higher file number (records documenting the history of these files have been lost). POCA Data - The Programmable Oscillator Control Assembly (POCA) set the (tunable) local oscillator in the DSN receivers. To recover Doppler shifts resulting from gravitational forces on the spacecraft or propagation through media with varying index of refraction, the receiver tuning must be known precisely. The VG2SPOC1.DAT file in the CALIB directory contains binary POCA data; file VG2SPOC2.TAB holds the same frequency data in an ASCII table format. Coordinate System ================= Original files (CRS files and HGA pointing files) were defined using the EME-1950 coordinates system. NAIF files, accessed with NAIF Toolkit software, allow extractions of positions and velocities in many coordinate systems. The basic radio data (ODR files) are independent of coordinate system. Software ======== The following main programs are included in the archive. All were written in FORTRAN 77; all have been tested and used on a Sun ULTRA-5 running Solaris 2.5.1. The SOFTWARE directory includes source code for these programs (and their subroutines) and a Unix Makefile which can be used to generate binary executables. For non-Sun/Solaris systems, the listings may serve as a starting point for versions which will run on the local machine. RDHDR: Reads and displays contents of individual ODR record headers. UNPK: Separates header and data components of records in an ODR file. CRS2ASC.F: Converts Univac binary CRS file to ASCII. Included only for historical purposes since the binary CRS file has not been included with this archive. CRS2LBL.F: Extracts information from ASCII CRS file useful in creating a PDS label. Included only for historical purposes. PREP_11_6.F: Program reformats Saturn data for use with Stanford quick-look and other processing software. Converts 8-bit samples in 5056-byte records to 16-bit samples in 1024-byte records, optionally corrects for missing or extra samples (analog tape dropout artifacts), and creates header record. Media/Format ============ The archival data set is written on CD-WO media using GEAR software and a Yamaha writer. The CD-WO volumes conform to ISO 9660 standards.

These data are available on-line from the Planetary Data System (PDS) at:

Alternate Names

  • VG2-S-RSS-1-ROCC-V1.0


  • Planetary Science: Fields and Particles

Additional Information



Questions and comments about this data collection can be directed to: Dr. Edwin V. Bell, II



NameRoleOriginal AffiliationE-mail
Prof. G. Leonard TylerData ProviderStanford
Dr. Richard A. SimpsonGeneral ContactStanford
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