Voyager 1 1-hr Averaged Triaxial Fluxgate Magnetometer (MAG) Interplanetary Magnetic Field in ASCII Format

This data set contains hour averages of the interplanetary magnetic
field (IMF) measurements obtained by the triaxial fluxgate magnetometer
experiment on Voyager 1. 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].