NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header



Availability: Archived at NSSDC, accessible from elsewhere

Time span: 1979-03-03 to 1979-03-16


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

Version 1.1 ----------This version 1.1 data set replaces the version 1.0 data set (DATA_SET_ID = VG1-J-MAG-4-48.0SEC) previously archived with PDS. Changes to this version include the addition of data columns not included in version 1.0, the modification of time format and flag values, and upgrade of associated labels and catalog templates to PDS version 3.2. Data Set Overview ================= This data set includes calibrated magnetic field data acquired by the Voyager 1 Low Field Magnetometer (LFM) during the Jupiter encounter. Coverage begins in the solar wind inbound to Jupiter and continues past the last outbound bowshock crossing. The data are in System III (1965) (SYS3) coordinates and have been averaged from the 9.6 second summary data to a 48 second sample rate. All magnetic field measurements are given in nanoTesla (nT). The magnetic field data are calibrated (see the calibration description included in the Voyager 1 Magnetometer instrument catalog file for details). Ephemeris data, provided in 96 second sampled System III (1965) coordinates, have been merged into the data files for this data set. The ephemeris data, generated from Voyager 1 SEDR and provided by the Voyager MAG Team, are part of the data set VG1-J-POS-6-SUMM-S3COORDS-V1.1. The position vectors for times at which ephemeris is not provided have been flagged. Parameters ========== The full LFM instrument sample rate is 1 sample per 0.06 seconds. Full telemetry resolution 'detail' data must be obtained from the instrument team. For this data set, the data have been resampled to 48 seconds from 9.6 second averages. The 9.6 second data were resampled from 1.92 second averages which were in turn resampled from the detail data. The LFM has eight dynamic ranges. The instrument is designed switch between dynamic ranges automatically depending upon the observed magnetic field magnitude and fluctuations. Instrument digitization uncertainty depends upon dynamic range as indicated in the following table (from [BEHANNONETAL1977]). ----------------------------------------------LFM Dynamic ranges and quantization uncertainty ----------------------------------------------Range (nT) Quantization (nT) ----------------------------------------------1. +/- 8.8 +/- .0022 2. +/- 26 +/- .0063 3. +/- 79 +/- .019 4. +/- 240 +/- .059 5. +/- 710 +/- .173 6. +/- 2100 +/- .513 7. +/- 6400 +/- 1.56 8. +/- 50,000 +/- 12.2 Processing ========== Voyager EDR's undergo the following processing in order to produce these 48 second averaged summary data: * Read EDR * Unpack header block (rec. id, s/c id, tel. mode, FDS counts, data flags) * Convert selected time tags to integer time (yy/ddd/hh:mm:ss.fff) * Unpack sub-header block (MAG status words, plasma data) * Unpack science block (MAG counts) * Convert counts to gammas * Apply sensor and boom alignment matrices * Rotate (optional) 1.92 second averages while averaging detail gammas to create 1.92 second averages * Average 1.92 second data to 9.6 seconds, then 9.6 second data to 48 seconds * Write Summary record Counts are measured onboard using 12 bit words that may represent values ranging from 0-4096. Integer counts are converted to magnetic field units (gammas) by subtracting a zero offset, from the measured MAG value and multiplying this difference by the sensitivity of the instrument. Data ==== The data files are given in ASCII, fixed field width, comma delimited tables. The record structure is described in the following table: -------------------------------------------------------------------48 Second System III (1965) Coordinates -------------------------------------------------------------------Column Type Description <units> -------------------------------------------------------------------time a23 spacecraft event time (UT) of the sample in the format: yyyy-mm-ddThh:mm:ss.sss sclk a12 spacecraft clock in the format: MOD65536:MOD60:FDS-LINE mag_id i1 magnetometer ID (1 = LFM, 2 = HFM) Br f9.3 average of detail magnetic field R component in nT Btheta f9.3 average of detail magnetic field Theta component in nT Bphi f9.3 average of detail magnetic field Phi component in nT Bmag f9.3 magnitude of the averaged magnetic field components in nT avg_Bmag f9.3 average of the magnetic field magnitude over the averaging interval in nT Delta f7.3 spacecraft centered heliographic magnetic field latitude in degrees: Delta = asin(Bz/Bmag)* Lambda f7.3 spacecraft centered heliographic magnetic field longitude in degrees: Lambda = atan(By/Bx)* rms_Br f8.3 root-mean-square deviation of Br over the averaging interval in nT rms_Bt f8.3 root-mean-square deviation of Btheta over the averaging interval in nT rms_Bp f8.3 root-mean-square deviation of Bphi over the averaging interval in nT SC R f7.3 spacecraft range from Jupiter in Jovian radii SC LAT f7.3 spacecraft SYS3 latitude in degrees SC LON f7.3 spacecraft SYS3 west longitude in degrees npts i2 number of detail points in the average dflag a8 8-byte character string which indicates software or spacecraft hardware intervention which reduces confidence in the data * while Br, Btheta, and Bphi are spherical coordinates, the angles Delta and Lambda are derived from Cartesian coordinates Ancillary Data ============== An ancillary data file containing the derived spacecraft magnetic field is provided with this data at a 48 second sample rate. These data provide zero level offsets used in the data processing. Spacecraft field data is provided in spacecraft coordinates as follows: -------------------------------------------------------------------48 Second Spacecraft Field (Payload) Averages -------------------------------------------------------------------Column Type Description <units> -------------------------------------------------------------------time a23 spacecraft event time (UT) of the sample in the format: yyyy-mm-ddThh:mm:ss.sss sclk a12 spacecraft clock in the format: MOD65536:MOD60:FDS-LINE mag_id i1 magnetometer ID (1 = LFM, 2 = HFM) Bx 1pe10.3 average Bx spacecraft field in nT (payload coords.) By 1pe10.3 average By spacecraft field in nT (payload coords.) Bz 1pe10.3 average Bz spacecraft field in nT (payload coords.) Bmag 1pe10.3 magnitude of spacecraft field in nT rms_Bx 1pe10.3 root-mean-square deviation of Bx over the averaging interval in nT rms_By 1pe10.3 root-mean-square deviation of By over the averaging interval in nT rms_Bz 1pe10.3 root-mean-square deviation of Bz over the averaging interval in nT npts i4 number of points in the average Coordinate Systems ================== The magnetic field data are provided in a conventional, right handed, spherical coordinate system with vectors R, Theta, and Phi. This system is sometimes referred to as System III (1965) right handed coordinates. The magnetic field vectors are: Br - radial B-field component (along the Jupiter to spacecraft line) positive away from Jupiter Btheta - North/South (SYS3) B-field component, positive southward Bphi - azimuthal (SYS3) B-field component, positive eastward SYS3 position, is given in a left-handed spherical system. Longitude (i.e. West longitude) is defined such that it appears to increase with time for a stationary observer [DESSLER1983]. The SYS3 1965 prime meridian is the sub-Earth longitude of 1965-01-01 00:00 UT. The spin rate (which was determined from the rotation rate of the magnetic field) is 9 hrs 55 min 29.719 sec. SYS3 position is given in terms of the following: R - spacecraft to Jupiter center-of-mass range in Jovian radii (1 Rj = 71942 km) LAT - spacecraft jovicentric latitude (positive northward) LON - spacecraft jovicentric west longitude The Jupiter System III coordinate system is described in Appendix B (p. 498) of [DESSLER1983]. References ========== [NESSETAL1979] Ness, N.F., M.H. Acuna, R.P. Lepping, L.F. Burlaga, K.W. Behannon, and F.M. Neubauer, Magnetic Field Studies at Jupiter by Voyager 1: Preliminary Results, Science, Vol. 204, p. 982, 1979. [LEPPINGETAL1981] Lepping, R.P., L.F. Burlaga, L.W. Klein, J. Jessen, and C.C. Goodrich, Observations of the Magnetic Field and Plasma Flow in Jupiter's Magnetosheath, J. Geophys. Res., Vol. 86, p. 8141, 1981. [CONNERNEYETAL1981] Connerney, J.E.P., M.H. Acuna, and N.F. Ness, Modeling the Jovian Current Sheet and Inner Magnetosphere, J. Geophys. Res., Vol. 86, p. 8370, 1981. [BEHANNONETAL1981] Behannon, K.W., L.F. Burlaga, and N.F. Ness, The Jovian Magnetotail and Its Current Sheet, J. Geophys. Res., Vol. 86, p. 8385, 1981. [DESSLER1983] Dessler, A.J., Physics of Jovian Magnetosphere Coordinate Systems, Physics of the Jovian Magnetosphere, 1983.

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

Alternate Names

  • VG1-J-MAG-4-SUMM-S3COORDS-48.0SEC-V1.1


  • 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
Dr. Norman F. NessData ProviderUniversity of
[] NASA Logo -