Data Set Overview
  =================
    This dataset contains data acquired by the Galileo Magnetometer
    from the Earth 2 encounter. The data have benn averaged down to
    twenty second resolution from the 7.68 kB Low Rate Science (LRS)
    real time telemetry mode. These data have been fully processed to
    remove instrument response function characteristics and
    interference from magnetic sources aboard the spacecraft. The data
    are provided in both Geocentric Solar Ecliptic (GSE) and
    Geocentric Solar Magnetic (GSM) coordinates. Trajectory data has
    been attached to this data for easier use. Trajectory data which
    was at a sample rate of once per minute, was linearly interpolated
    to match the 20 second sample rate of this data.

    Primary Reference: [KIVELSONETAL1993]


  Data
  ====

    -----------------------------------------------------------------
    Table 1. Data record structure
    -----------------------------------------------------------------
    Column    type     description
    -----------------------------------------------------------------
    time      char     S/C event time (UT) in PDS time format:
                       yyyy-mm-ddThh:mm:ss.sssZ
    Bx        float    X component GSE or GSM coords. (20s res) 
    By_gse    float    Y component GSE coordinates (20s res) 
    Bz_gse    float    Z component GSE coordinates (20s res) 
    By_gsm    float    Y component GSM coordinates (20s res) 
    Bz_gsm    float    Z component GSM coordinates (20s res) 
    Bmag      float    |B| Magnitude of B (20s res) 
    stBx      float    Standard deviation for: Bx 
    stBy_gse  float    Standard deviation for: By_gse 
    stBz_gse  float    Standard deviation for: Bz_gse 
    stBy_gsm  float    Standard deviation for: By_gsm 
    stBz_gsm  float    Standard deviation for: Bz_gsm 
    stBmag    float    Standard deviation for: Bmag 
    npts      int      Points in average
    dqf       int      Data quality flag
    X         float    X component GSE and GSM 
    Y_gse     float    Y component GSE coordinates 
    Z_gse     float    Z component GSE coordinates 
    Y_gsm     float    Y component GSM coordinates 
    Z_gsm     float    Z component GSM coordinates 

    Data Acquisition:

    The data for this dataset were acquired as part of the normal
    instrument calibration activities associated with the cruise to
    Jupiter. As such, the instrument was commonly configured in modes
    which required calibration even though they may not have been the
    optimal mode for science data acquisition. The Galileo
    magnetometer has 8 possible LRS acquisition configurations
    (modes). There are two sensor triads mounted 7 and 11 meters from
    the rotor spin axis (inboard and outboard) along the boom. Each of
    the sensor triads has two gain states (high and low). In addition,
    the sensor triads can be 'flipped' to move the spacecraft
    spin-axis aligned sensor into the spin plane and visa versa.
    Please see the instrument description for full details on the
    instrument, sensors, and geometries. The combinations of sensor,
    gain state, and flip direction form modes.

    ------------------------------------------------------------------
    Table 2. Mode Characteristics
    ------------------------------------------------------------------
             Mode Name            Acronym       range     quantization
    ------------------------------------------------------------------
    Inboard,  left,  high range*    ILHR    +/- 16384 nT    8.0   nT
    Inboard,  right, high range*    IRHR    +/- 16384 nT    8.0   nT
    Inboard,  left,  low  range*    ILLR    +/-   512 nT    0.25  nT
    Inboard,  right, low  range*    IRLR    +/-   512 nT    0.25  nT
    Outboard, left,  high range*    ULHR    +/-   512 nT    0.25  nT
    Outboard, right, high range*    URHR    +/-   512 nT    0.25  nT
    Outboard, left,  low  range*    ULLR    +/-    32 nT    0.008 nT
    Outboard, right, low  range*    URLR    +/-    32 nT    0.008 nT

    ------------------------------------------
    Table 3. Mode change history
    ------------------------------------------
    s/c clock         date/time          mode
    ------------------------------------------

    * range is the opposite of gain

    In addition to exercising the various instrument modes during the
    first earth encounter, numerous instrument calibration activities
    were performed. These include using both the internal and external
    calibration coils. Data corrupted by the use of the calibration
    coils or by the flipper motor have been removed from the processed
    data. These data have been archived with the Experimenter Data
    Records (EDR) and other Magnetometer team raw data archive
    products.

    Data Sampling:

    These data have been resampled to 20 seconds using overlapping 40
    second averages of the high-resolution (~2/3 second) data. The
    time tag represents the center of the averaging interval. For a
    discussion regarding the high-resolution data please refer to the
    catalog file for the GO-E-MAG-3-RDR-E2-HIGHRES-V1.0 data set
    (/CATALOG/MAG_E2_HIGHRES_DS.CAT).


  Coordinate Systems
  ==================
    Geocentric Solar Ecliptic (GSE) and Geocentric Solar Magnetic
    (GSM) are related earth centered coordinate systems. Both the GSE
    and GSM X directions are taken along the Earth - Sun line,
    positive towards the Sun. The GSE Z direction is parallel to the
    ecliptic normal, positive northward, and Y completes the
    right-handed set (towards dusk). For GSM, the X-Z plane contains
    the Earth's dipole moment vector, positive northward, and Y
    completes the right-handed set. GSE coordinates are commonly used
    for analyzing the solar wind near the Earth and GSM coordinates
    are used when analyzing data inside the Earth's bow shock.


  Data Processing
  ===============
    These data have been processed from the PDS dataset:
    'GO-E/V/A-MAG-3-RDR-HIRES-V1.0'

    In order to generate the IRC processed dataset, the following
    procedure was followed:

    1)  Sensor zero level corrections were subtracted from the raw
        data,
    2)  Data were converted to nanoTesla,
    3)  A coupling matrix which orthogonalizes the data and corrects
        for gains was applied to the data (calibration applied),
    4)  Magnetic sources associated with the spacecraft were subtracted
        from the data,
    5)  Data were 'despun' into inertial rotor coordinates,

    Lastly, in order to generate the processed data in GSE/GSM
    coordinates the data were transformed into geophysical coordinates
    and averaged to twenty second resolution.

    For a more detailed description of these proceedures please refer
    to the file /CALIB/HR_PROC.TXT. For more information regarding
    data calibration please refer to [KEPKOETAL1996].

Review
  ======
    These data have been reviewed by the instrument team and are of
    the highest quality that can be generated at this time. Science
    results based on some of these data have been published in several
    journals (Science, JGR, etc.). After submission to PDS, these data
    successfully completed the peer review process.


  Confidence Level Overview
  =========================
    Each aspect of the data processing sequence can be analyzed to
    determine its maximum possible error contribution. In theory,
    these errors could be summed to provide estimates of the maximum
    error for each data point. Error analysis for these data have not
    been taken to that level.

    The MAG team believes that calibrations (sensor geometry and
    gains) are good enough that they produce a negligible source of
    data error. In addition, that the coordinate system
    transformations which are derived from the SPICE kernels and
    Toolkit are believed to be negligible sources of error in the
    magnetic field vectors. The most significant sources of error are
    those associated with magnetic sources aboard the spacecraft,
    especially those with temporal or spacecraft orientation
    variations. The next greatest contributor of error is the data
    from the AACS which affects our knowledge of the spacecraft
    orientation and hence rotates the magnetic field vector. Lastly,
    telemetry or software errors which produce 'spikes' or bit errors
    in the data are error sources.


  Data Coverage and Quality
  =========================
    In regions where the magnetic sources associated with the
    spacecraft are fairly constant, magnetic interference is probably
    reduced by data processing to better than 0.05 nT at the inboard
    sensors. In these same regions, sensor zero levels (offsets) are
    known equally well. The data processing software does a fairly
    good job of removing all currently identified sources of magnetic
    interference. However, there are some time intervals when the zero
    levels of the spin plane sensors show large variations (1-5 nT) on
    short time scales (minutes to hours). After a while (hours to
    days) the offsets return to their nominal levels. The source of
    these magnetic fields has not yet been identified. The method of
    removing offsets from the spin plane sensors does remove these
    effects, but the method of determining the spin axis aligned
    sensor offsets does not. In regions where large variations are
    detected in the spin plane sensors it is reasonable to assume that
    similar variations are taking place in the spin axis aligned
    sensor. Averaging reduces the level of the interference, though
    it may not remove it completely.

    A second problem in determining and removing the magnetic
    interference associated with the spacecraft is the movement of
    these magnetic sources. At the Earth 2 encounter an extensive test
    was done to determine the interference patterns as a function of
    the position of the magnetic sources. Data was taken with the scan
    platform at fifteen degree intervals and the interference was
    successfully modeled.


  Limitations
  ===========
    MAG data processing software creates a data quality flag (DQF)
    which is an assessment of AACS and telemetry error source
    contamination of a given data point. This number is binary integer
    where each bit indicates the presence or absence of some error
    source. A DQF is assigned to each point of the high-res (about 2/3
    sec) data. The values given in this data set is the highest value
    for the averaged interval.

    The number 0 represents the absence of all error sources which are
    tested. The higher order bit (larger number) error sources are
    considered to be more significant error sources. Data are examined
    for gradients in the field which might be associated with
    telemetry bit errors, for regions of bad AACS angles, and for
    completely missing data. If the error is considered completely
    unrecoverable, the data values are replaced with a missing data
    flag. In the case of a flag in the rotor spin angle, the vector
    components may be flagged but the magnitude is still valid. Table
    4 is a list of all of the error checks and the bits they set in
    the DQF field.

    ------------------------------------------------------------------
    Table 4. Data Quality Flag (DQF) Values
    ------------------------------------------------------------------
    DQF_GOOD_DATA                 0  Good data
    DQF_BX_GRAD_WARNING         2^0  Component gradient warning
    DQF_BY_GRAD_WARNING         2^1  Component gradient warning
    DQF_BZ_GRAD_WARNING         2^2  Component gradient warning
    DQF_INTERP_ROTATTR          2^3  Missing rotor RA interpolated
    DQF_INTERP_ROTATTD          2^4  Missing rotor DEC interpolated
    DQF_INTERP_SPINDELT         2^5  Missing rotor Spin Delta
                                     interpolated
    DQF_INTERP_SCRELCON         2^6  Missing Relative Cone angle
                                     interpolated
    DQF_INTERP_SCRELCLK         2^7  Missing Relative Clock angle
                                     interpolated
    DQF_INTERP_ROTATTT          2^8  Missing rotor Twist interpolated
    DQF_INTERP_SPINANGL         2^9  Missing rotor Spin interpolated
    DQF_ROTATTR_FLAG            2^10 Missing rotor RA flagged
    DQF_ROTATTD_FLAG            2^11 Missing rotor DEC flagged
    DQF_SPINDELT_FLAG           2^12 Missing rotor Spin Delta flagged
    DQF_SCRELCON_FLAG           2^13 Missing Relative Cone angle
                                     flagged
    DQF_SCRELCLK_FLAG           2^14 Missing Relative Clock angle
                                     flagged
    DQF_ROTATTT_FLAG            2^15 Missing rotor Twist flagged
    DQF_AACS_TELEMETRY_HIT_FLAG 2^16 Telemetry hit in AACS record
    DQF_MAG_TELEMETRY_HIT_FLAG  2^17 Telemetry hit in mag record
    DQF_SPINANGL_FLAG           2^18 Missing rotor Spin flagged

    DQF_BX_GRAD_ERROR           2^25 Component gradient error
    DQF_BY_GRAD_ERROR           2^26 Component gradient error
    DQF_BZ_GRAD_ERROR           2^27 Component gradient error
    DQF_BX_FLAG                 2^28 Component flagged
    DQF_BY_FLAG                 2^29 Component flagged
    DQF_BZ_FLAG                 2^30 Component flagged

    Magnetic field gradient warning or error levels are set during the
    data processing according to expected variances depending on the
    region of space.  In the solar wind, gradient warnings are usually
    issued at gradients of 10 nT/sec and errors at 15 nT/sec. In the
    magnetosheath, these values may be 50 percent larger. In the inner
    magnetosphere, these dqf flags may be completely turned off.
    Similarly, AACS angles are interpolated across gaps during the
    processing if the gap length is relatively short (less than 10
    minutes typically). If the gaps in spacecraft attitude are long,
    the AACS angles are flagged and not interpolated.

    Errors associated with AACS angles have various effects on the
    data. The rotor right ascension and declination are crucial to the
    understanding of the spacecraft orientation. Fortunately, these
    angles are slowly varying and can be interpolated to better than 1
    degree of accuracy for long (many hour) time periods except near
    major spacecraft maneuvers. The relative clock and cone angles are
    used to remove scan platform interference. In their absence, no
    interference is removed (+/- 0.15 nT error possible in each
    component). The rotor motion spin delta is used to determine the
    instantaneous spin frequency for the phase delay computation. In
    its absence, the last known phase delay is applied to the current
    data point. The rotor spin angle and twist angle must be present
    in order to despin the data. These angles are generally not
    interpolated for more than ten minutes because the rotor spin
    period drifts over time periods on this order.