Data Set Overview
      =================
      This data set consists of magnetic field vector data recorded by
      the Vector Helium Magnetometer onboard the Pioneer 11 spacecraft,
      during the close encounter to Jupiter (inside 7 RJ).  The vector
      data are provided in Jupiter-centered JG coordinates (see
      descriptions in Sections of Data Format and Coordinate System for
      Data).  Also included are the spacecraft trajectory data (distance
      from Jupiter, latitude, and longitude) in the same coordinates.


      Data Sampling
      ==============
      The magnetometer measures the three field components over a
      frequency range from 0 to 10 Hz.  At encounter the data rate was
      1024 bits/sec and the magnetometer sampling rate was one vector
      measurement every 3/16 second, corresponding to 5.33 samples/sec.

      The NSSDC documentation does not contain information about what
      data resolution this data set (1 minute) is averaged from.


      Data Processing
      ===============
      No detailed information of data processing is found in the NSSDC
      documentation pertinent to this data set.

      Pioneer 11 spacecraft was operating under a spin-stablized
      condition and had a spin period of 7.7 second.


      Data Format
      ============
      The Pioneer 11 magnetometer data for the close encounter to
      Jupiter were originally written on a 9-track, 1600 bpi, ASCII
      encoded magnetic tape.  The original file was re-formatted into
      a new ASCII file named P11_HVM_JUP_NEAR_ENC_1MIN.TAB which
      contains the following data columns:
      --------------------------------------------------------------------
      Column  Column   Column
      Name    Format   Description
      --------------------------------------------------------------------
      TIME    A24      Ground received time in yyyy-mm-ddThh:mm:ss.sss
      R       F12.4    Distance of Pioneer 11 from Jupiter in Rj
      LAT     F12.4    Latitude of Pioneer 11 in JG coordinates
      LON     F12.4    Longitude of Pioneer 11 in JG coordinates
      BX      F12.4    X component of the magnetic field in JG coordinates
      BY      F12.4    Y component of the magnetic field in JG coordinates
      Bz      F12.4    Z component of the magnetic field in JG coordinates
      --------------------------------------------------------------------


      Coordinate System for Data
      ===========================
      JG coordinates is defined as the X axis in the direction of G, the
      equatorial vector lying in the System III Prime Meridian, 1957.0;
      the Z axis in the direction of J, the spin axis of Jupiter; and
      the Y axis parallel to Jupiter's equatorial plane and completing
      the right-handed orthogonal system.


      Ancillary Data
      ==============
      There is no ancillary data associated with this data set.


      Instrument Calibration
      ======================
      The in-flight calibration consists of impressing eight precisely
      known currents on the sensor coil system and measuring the resulting
      fields with the magnetometer.  The instrument is designed to carry
      out a nominal mission with only one instrument-on command.  The
      instrument comes on in the automatic ranging/spectrum analyzer
      mode and automatically ranges to the proper scale by comparing
      the +X and |Z| axis outputs with fixed reference voltages.  The
      only function commands sent to this instrument during the Pioneer
      F&G missions were those to initiate the in-flight calibration
      sequence periodically during the cruise phase.  At the conclusion
      of this sequence the instrument automatically returned to the
      automatic ranging mode.  A 6-bit digital house-keeping word
      indicates the operating mode of the instrument.

      The in-flight calibration onboard the Pioneer spacecraft was done
      by ground command once or twice a week.  The low range sensors were
      calibrated at field magnitude of 13 GAMMA and 26 GAMMA during the
      interplanetary cruise period.  While the high range sensors were
      calibrated near planetary encounter where the field magnitude was
      as high as +- 43,000 GAMMA and 86,800 GAMMA. There are two kind of
      instrument calibration parameters, sensor scale factor (gain) and
      offset.

      The conventional approach to checking the magnetometer scale
      factors in flight is to apply calibration field changes, dB to
      the sensors so that the corresponding voltage change dV can be
      determined.  Normally several step changes are applied sequentially
      so that the linearity can be tested directly. After two years of
      in-flight calibrations, no change has been detected in the Pioneer
      10 or 11 scale factors which were then known to an accuracy of
      1 percent or better.

      The sensor offsets were determined in-flight using two different
      techniques.   For the two sensors in the spin plane, the offset
      was calculated by averaging the spinning data in a time interval
      of an integral number of spin period.  The offset of the spin axis
      sensor was determined by an adaptation of a variance technique
      developed by L. Davis [BELCHER1973].  The essential assumption
      was made that over short intervals of time (5 minutes), the
      fluctuations in the interplanetary field are principally changes
      in direction and tend to conserve the magnitude of the field.

Confidence Level Overview
      =========================
      The vector helium magnetometer noise spectrum is independent of
      frequency (white) with a field equivalent power spectral density
      of 10**-4 GAMMA**2/HZ.  For signal bandwidths less than 1 Hz,
      corresponding for example to values averaged over a few seconds
      or more, fields smaller than 0.01 GAMMA can be detected.

      The maximum relative error of the magnetometer sensors is given by
                 dB/B <= dB0/B + dk/k
      where B0 is the total offset error and dk is the scale factor error.
      The scale factor accuracy is as good as 1%.  And the total offset
      error is mainly caused by the spin axis sensor error because it
      is not readily determined as the two in spin-plane sensors.  The
      ratio of the standard deviation of the offset in spinning axis
      to the field magnitude is about 0.05.  Thus, the maximum relative
      error in the magnetic field measurement is 0.06.

      There is no flagged values in this data set.