Voyager 1 9.6-s Averaged Triaxial Fluxgate Magnetometer (MAG) Interplanetary Magnetic Field in Binary Format

This magnetic field data set contains 9.6 second averages that are created from 1.92 second averages. It includes the Voyager spacecraft number (1 or 2), the date-time in\ndecimal year (90.00000 is day 1 of 1990), the magnetic field strength F1\ncomputed from high-resolution magnitudes, the elevation and azimuth angles\n(degrees) in heliographic (RTN) coordinates, and the magnetic field strength F2\ncomputed from hour averages of the components. The vector components of B can be\ncomputed from F2 and the two angles. Elevation angle is the latitude angle above\nor below the solar equatorial plane, and azimuth angle is in the direction\norbital motion around the Sun from the projection of the Sun-to-spacecraft axis\ninto the solar equatorial plane. The Voyager MAG experiment and coordinates are\nfurther described in the following publication:  Behannon, K.W., M.H. Acuna,\nL.F. Burlaga, R.P. Lepping, N.F. Ness, and F.M. Neubauer, Magnetic-Field\nExperiment for Voyager-1 and Voyager-2, Space Science Reviews, 21 (3), 235-257,\n1977...At the time of experiment proposal, it was expected that the required\naccuracy of the measurements would be 0.1 nT, determined by the combined noise\nof the sensors and the spacecraft field. The spacecraft magnetic field at the\noutboard magnetic field sensor, referred to as the primary unit, was expected to\nbe 0.2 nT and highly variable, consistent with current estimates. Hence, the\ndual magnetometer design (Ness et al., 1971, 1973; Behannon et al. 1977). ..At\ndistances > 40 AU, the heliospheric magnetic fields are generally much weaker\nthan 0.4 nT; the average magnetic field strength near 40 AU and 85 AU is about\n0.15 nT and 0.05 nT, respectively. The use of roll calibrations lasting about 6\nhours permits determination of the effective zero levels for the two independent\nmagnetic axes that are perpendicular to the roll axis (which is nearly parallel\nto the radius vector to the Sun) at intervals of about 3 months. There is no\nroll calibration for the third magnetic axis. Comparison of the two derived\nmagnetic vectors from the two magnetometers permits validation of the primary\nmagnetometer data with an accuracy of 0.02 to 0.05 nT. A discussion of the\nuncertainties that must be considered when using these data is given in the\nAppendix of Burlaga et al. [1994] and in Appendix A of Burlaga et al. [2002].\n..References: ..Behannon, K.W., M.H. Acuna, L.F. Burlaga, R.P. Lepping, N.F.\nNess, and F.M. Neubauer, Magnetic-Field Experiment for Voyager-1 and Voyager-2,\nSpace Science Reviews, 21 (3), 235-257, 1977. ..Burlaga, L.F., Merged\ninteraction regions and large-scale magnetic field fluctuations during 1991 -\nVoyager-2 observations, J. Geophys. Res., 99 (A10), 19341-19350, 1994.\n..Burlaga, L.F., N.F. Ness, Y.-M. Wang, and N.R. Sheeley Jr., Heliospheric\nmagnetic field strength and polarity from 1 to 81 AU during the ascending phase\nof solar cycle 23, J. Geophys. Res., 107 (A11), 1410, 2002. ..Ness, N., K.W.\nBehannon, R. Lepping, and K.H. Schatten, J. Geophys. Res., 76, 3564, 1971.\n..Ness et al., 1973\nAt distances > 40 AU, the heliospheric magnetic fields are generally much weaker\nthan 0.4 nT; the average magnetic field strength near 40 AU and 85 AU is about\n0.15 nT and 0.05 nT, respectively. The use of roll calibrations lasting  about 6\nhours permits determination of the effective zero levels for the two independent\nmagnetic axes that are perpendicular to the roll axis (which is nearly parallel\nto the radius vector to the Sun) at intervals of about 3 months. There is no\nroll calibration for the third magnetic axis. Comparison of the two derived\nmagnetic vectors from the two magnetometers permits validation of the primary\nmagnetometer data with an accuracy of 0.02 to 0.05 nT. A discussion of the\nuncertainties that must be considered when using these data is given in the\nAppendix of Burlaga et al. [1994] and in Appendix A of Burlaga et al. [2002].\nCOORDINATE SYSTEMS:  Interplanetary magnetic field studies make use of two\nimportant coordinate systems, the Inertial Heliographic (IHG) coordinate system\nand the Heliographic (HG) coordinate system.\nThe IHG coordinate system is use to define the spacecraft's position.  The IHG\nsystem is defined with its origin at the Sun.  There are three orthogonal axes,\nX(IHG), Y(IHG), and Z(IHG).  The Z(IHG) axis points northward along the Sun's \nspin axis.  The X(IHG) - Y(IHG) plane lays in the solar equatorial plane.  The\nintersection of the solar equatorial plane with the ecliptic plane defines a\nline, the longitude of the ascending node, which is taken to be the X(IHG) axis.\nThe X(IHG) axis drifts slowly with time, approximately one degree per 72 years.\nMagnetic field orientation is defined in relation to the spacecraft.  Drawing a\nline from the Sun's center (IHG origin) to the spacecraft defines the X axis of\nthe HG coordinate system.  The HG coordinate system is defined with its origin\ncentered at the spacecraft.  Three orthogonal axes are defined, X(HG), Y(HG),\nand Z(HG).  The X(HG) axis points radially away from the Sun and the Y(HG) axis\nis parallel to the solar equatorial plane and therefore parallel to the\nX(IHG)-Y(IHG) plane too.  The Z(HG) axis is chosen to complete the orthonormal\ntriad. \nAn excellent reference guide with diagrams explaining the IHG and HG systems may\nbe found in Space and Science Reviews, Volume 39 (1984), pages 255-316, MHD\nProcesses in the Outer Heliosphere,  L. F. Burlaga.

Tags: magneticfield
Organization: National Aeronautics and Space Administration