| DATA_SET_DESCRIPTION |
Version 1.1
-----------
This version 1.1 data set replaces the version 1.0 data set
(DATA_SET_ID = VG1-J-MAG-4-9.60SEC) 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
1.92 second summary data to a 9.6 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).
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
9.6 seconds from 1.92 second summary data. The 1.92 second data 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 9.6 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
* 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:
--------------------------------------------------------------------
9.6 Second System III (1965) Coordinates
--------------------------------------------------------------------
Column Type Description
--------------------------------------------------------------------
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
npts i2 number of detail points in the average
* 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
--------------------------------------------------------------------
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
==================
These 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
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.
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