DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set includes calibrated magnetic field data acquired by
the Voyager 1 Low Field Magnetometer (LFM) during the Saturn
encounter. Coverage begins in the solar wind inbound to Saturn and
continues past the last outbound bowshock crossing. The data are in
Kronographic (L1) coordinates and have been averaged from the 9.6
second summary rate 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). This
data set supersedes VG1-S-MAG-4-48.0SEC
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.
Sampling Parameter Name : TIME
Data Set Parameter Name : MAGNETIC FIELD VECTOR
Sampling Parameter Resolution : 48.000000
Minimum Sampling Parameter : 19770820120000.000000
Maximum Sampling Parameter : UNK
Sampling Parameter Interval : 48.000000
Minimum Available Sampling Int : 0.060000
Data Set Parameter Unit : NANOTESLA
Noise Level : 0.006000
Sampling Parameter Unit : SECOND
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
Instrument Host ID : VG1
Data Set Parameter Name : MAGNETIC FIELD VECTOR
Instrument Parameter Name : MAGNETIC FIELD COMPONENT
Important Instrument Parameters : 1
Instrument Host ID : VG1
Data Set Parameter Name : MAGNETIC FIELD VECTOR
Instrument Parameter Name : WAVE MAGNETIC FIELD INTENSITY
Important Instrument Parameters : 1
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.
Processing Level Id : 4
Software Flag : Y
Processing Start Time : 1988-09-21
Source Data Set ID : N/A
Software : UNK
Product Data Set ID : VG1-S-MAG-4-48.0SEC
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 L1 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
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
--------------------------------------------------------------------
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 in Kronographic (L1) coordinates. L1 is
a conventional, right handed, Saturn-centered spherical coordinate
system with vectors R, Theta, and Phi. The magnetic field vectors
are:
Br - radial B-field component (along the Saturn to spacecraft
line) positive away from Saturn
Btheta - North/South (L1) B-field component, positive southward
Bphi - azimuthal (L1) B-field component, positive eastward
Trajectory is left handed and based upon the Saturn Longitude System
[DESCH&KAISER1981].
References
==========
The reference documents for this data set are:
[ACUNAETAL1981B] Acuna, M.H., J.E.P. Connerney, and N.F. Ness,
Topology of Saturn's Main Magnetic Field,
Nature, 292, 721, 1981.
[BEHANNONETAL1981B] Behannon, K.W., J.E.P. Connerney, and N.F.
Ness, Saturn's Magnetic Tail: Structure and
Dynamics, Nature, 292, 753, 1981.
[BEHANNONETAL1983] Behannon, K.W., R.P. Lepping, and N.F. Ness,
Structure and Dynamics of Saturn's Outer
Magnetosphere and Boundary Regions, J.
Geophys. Res., 88, 8791, 1983.
[CONNERNEYETAL1983] Connerney, J.E.P., M.H. Acuna, and N.F. Ness,
Currents in Saturn's Magnetosphere, J.
Geophys. Res., 88, 8779, 1983.
[LEPPINGETAL1981D] Lepping, R.P., L.F. Burlaga, and L.W. Klein,
Surface Waves on Saturn's Magnetopause,
Nature, 292, 750, 1981.
[NESSETAL1981] Ness, N.F., M.H. Acuna, R.P. Lepping, J.E.P.
Connerney, K.W. Behannon, L.F. Burlaga, and
F.M. Neubauer, Magnetic Field Studies by
Voyager 1: Preliminary Results at Saturn,
Science, 212, 211, 1981.
[NESSETAL1982B] Ness, N.F., M.H. Acuna, K.W. Behannon, L.F.
Burlaga, J.E.P. Connerney, R.P. Lepping, and
F.M. Neubauer, Magnetic Field Studies by
Voyager 2: Preliminary Results at Saturn,
Science, 215, 558, 1982.
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