Data Set Overview
    =================

      This data set contains hour averages of the interplanetary magnetic
      field (IMF) measurements obtained by the triaxial fluxgate magnetometer
      experiment on Voyager 2. Identical instruments on Voyager 1 and 2 were
      designed to measure the IMF between  Earth and Saturn (10 AU) during the
      primary Voyager mission. The  design and performance yielded absolute
      accuracies to better than < 0.1 nT. In general, each component of the
      hourly average has an uncertainty of up  to (+/- 0.05 nT) in the region
      beyond 10 AU. More accurate measurements can be  obtained by special
      processing of the data, but it was not feasible to do this for the
      entire data set included here. The magnetic field magnitude in nT is
      provided along with angles of the field vector in the spacecraft-
      centered Heliographic (HG) coordinate system, also known as RTN.

    Coordinate System
    =================

      Interplanetary magnetic field studies make use of two important
      coordinate systems, the Inertial Heliographic (IHG) coordinate system
      and the Heliographic (HG) coordinate system.

      The IHG coordinate system is use to define the spacecraft's position.
      The IHG system is defined with its origin at the Sun.  There are three
      orthogonal axes, X(IHG), Y(IHG), and Z(IHG).  The Z(IHG) axis points
      northward along the Sun's spin axis.  The X(IHG) - Y(IHG) plane lays in
      the solar equatorial plane.  The intersection of the solar equatorial
      plane with the ecliptic plane defines a line, the longitude of the
      ascending node, which is taken to be the X(IHG) axis.  The X(IHG) axis
      drifts slowly with time, approximately one degree per 72 years.

      Magnetic field orientation is defined in relation to the spacecraft.
      Drawing a line from the Sun's center (IHG origin) to the spacecraft
      defines the X axis of the HG coordinate system.  The HG coordinate
      system is defined with its origin centered at the spacecraft.  Three
      orthogonal axes are defined, X(HG), Y(HG), and Z(HG).  The X(HG) axis
      points radially away from the Sun and the Y(HG) axis is parallel to the
      solar equatorial plane and therefore parallel to the X(IHG)-Y(IHG) plane
      too.  The Z(HG) axis is chosen to complete the orthonormal triad.

      An excellent reference guide with diagrams explaining the IHG and HG
      systems may be found in Space and Science Reviews, Volume 39 (1984),
      pages 255-316, MHD Processes in the Outer Heliosphere, L. F. Burlaga
      [BURLAGA1984].

    Data Formats
    ============
      field    description (data before 1990)
      -----    ------------------------------
      1. s/c id  (1 = Voyager-1, 2 = Voyager-2)
      2. UTC     YY DDD HH where YY=year, DDD=day, and HH=hour
      3. X      X IHG position component (A.U. - IHG coordinates)
      4. Y      Y IHG position component (A.U. - IHG coordinates)
      5. Z      Z IHG position component (A.U. - IHG coordinates)
      6. Range  Heliocentric range = sqrt(X*X+Y*Y+Z*Z)
      7. F1     Field magnitude (nT)  ( avg(F2(48sec)) )
      8. F2     Field modulus (nT)  ( norm (B1,B2,B3) )
      9. delta  Latitudinal angle (degrees - HG coordinates)
     10. lambda Longitudinal angle (degrees - HG coordinates)

      field  descriptor (data after 1990)
      -----  ----------------------------
        1.   s/c identification (FLT1=Voyager 1)
                                (FLT2=Voyager 2)
        2.   Time (UTC) decimal year format (90.00000 is day 1 of 1990)
        3.   The magnetic field strength,  F1, computed from
               high-resolution observations.
        4.   The elevation angle (degrees) in heliographic coordinates.
        5.   The azimuthal angle (degrees) in heliographic coordinates.
        6.   The magnetic field strength, F2, computed from hour
               averages of the components. The components of B can be
               computed from F2 and the two angles.

      MAG field components may be recovered using F2, delta and lambda.

      BR = F2*COS(lambda)*COS(delta)      Fortran users need to convert
      BT = F2*SIN(lambda)*COS(delta)      degrees to radians before
      BN = F2*SIN(delta)                  using trig functions.

    Contact Information
    ===================

      Principal Investigator:

      Prof. Norman F. Ness
      Bartol Research Institute
      Univerity of Delaware
      Newark, Delaware 19716-4793
      Phone: (302) 831-8116
      Fax: (302) 831-1843
      Email: norman.ness@mus.udel.edu

      Data Contact:

      Dr. Len Burlaga
      Code 612.2
      NASA Goddard Space Flight Center
      Greenbelt, MD 20771
      Tel.: 301-286-5956
      Fax: 301-286-1433
      E-mail: len.burlaga@nasa.gov

    References
    ==========

      Behannon, K.W., M.H. Acuna, L.F. Burlaga, R.P. Lepping, N.F. Ness, and
      F.M. Neubauer, Magnetic-Field Experiment for Voyager-1 and Voyager-2,
      Space Science Reviews, 21 (3), 235-257, 1977.

      Burlaga, L.F., Merged interaction regions and large-scale magnetic
      field fluctuations during 1991 - Voyager-2 observations, J. Geophys.
      Res., 99 (A10), 19341-19350, 1994.

      Burlaga, L.F., N.F. Ness, Y.-M. Wang, and N.R. Sheeley Jr., Heliospheric
      magnetic field strength and polarity from 1 to 81 AU during the
      ascending phase of solar cycle 23, J. Geophys. Res., 107 (A11), 1410,
      2002.

      Ness, N., K.W. Behannon, R. Lepping, and K.H. Schatten, J. Geophys.
      Res., 76, 3564, 1971.

      Ness et al., 1973

    Acknowledgement
    ===============

       Use of these data in publications should be accompanied at minimum by
       acknowledgements of the National Space Science Data Center and the
       responsible Principal Investigator defined in the experiment
       documentation provided here.