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

The Voyager Magnetometer Investigation (Principal Investigator, Norman F. Ness) makes available archival Data through the National Space Science Data Center (NSSDC) located at NASA/GSFC as well as through the Planetary Data System (PDS) and other Channels. The primary Archive Format, referred to as a "Summary Tape" or "conjoint Summary Tape" has been used consistently since the Beginning of the Voyager Mission to the outer Planets in 1977. This Format makes available Magnetometer Observations, Supplementary Engineering and Ephemeris Data in one Data File, and it is one Product of Voyager Magnetometer Routine Data Processing. Users are referred to the Summary Format Data for all Data Requirements with one Exception: Neptune Encounter High-Field Observations. Neptune close approach Observations are archived separately and in a different Format from that with which many are familiar. This High-Field Archive is described here.

The special Demands of the Neptune Encounter Flyby exceeded (finally) the Capabilities of the Routine Data Processing System conceived and implemented in the mid 1970s. As a Result, it was necessary to implement an additional Data Processing System with which the near-encounter, High-Field Magnetometer Observations were processed. The Data Products available with this new Data Processing System are not available in the same Format as the standard Voyager Magnetometer Observations; thus the need for a separate Archive and a new Format Description. We appreciate the Desirability of a consistent Archive Format, but find no reasonable alternative to the present Solution. We expect, however, that Users interested in near Encounter Observations will find this new Format both useful and easy to assimilate.

The Magnetic Fields Investigation on Voyager carries a Total of four Tri-axial Ring Core Fluxgate Magnetometers: two identical High-Field Magnetometers mounted on the Spacecraft Body (HFMs) and two identical Low Field Magnetometers (LFMs) arranged on a 13 m Boom (Behannon et al., 1977). The two LFMs automatically Step through a Total of eight Dynamic Ranges (ranges 0 through 7) in response to changes in the measured Field, starting with a nominal Dynamic Range of 8 nT, and increasing to a nominal Dynamic Range of 50,000 nT. The two HFMs each operate in two Dynamic Ranges (ranges 0 and 1) with nominal Values of 50,000 nT and 200,000 nT. In the Neptune Encounter Mode, each Magnetometer was sampled periodically with a Temporal Resolution of between 0.6 s and 0.06 s, and analog-to-digital converted with 12-bit Resolution for subsequent Telemetry. The Magnitude of the maximum observed Field at Neptune (approximately 10,000 nT) was sufficiently large that Data from all four of the Magnetometers proved useful.

• Parameters

• ==========

• Derived Parameters

• ==================

+-------------------------------------------------------------+
| Parameter Characteristics | Value |

| Sampling Parameter Name | TIME |
| Sampling Parameter Resolution | 12.0 SECONDS |
| Minimum Sampling Parameter | 19770820120000.000000 |
| Maximum Sampling Parameter | UNK |
| Sampling Parameter Interval | 12.0 SECONDS |
| Minimum Available Sampling Interval | 0.060000 SECONDS |
| Data Set Parameter Name | MAGNETIC FIELD VECTOR |
| Noise Level | 0.006000 NT |
| Data Set Parameter Unit | NT |
+-------------------------------------------------------------+

Magnetic Field Vector: A derived Parameter which combines the three orthogonal Magnetic Field Component Measurements.

• Measured Parameters
• ===================

Magnetic Field Component: A measured Parameter equaling the Magnetic Field Strength along a particular Axis Direction. Usually the three orthogonal Axis Components are measured by three different Sensors.

• Data

• ====

• Magnetometer Data Product

• ctime - Decimal seconds past 1966-01-02T00:00:00, an internal Time Format

• SCET - Spacecraft Event Time, PDS/ISO Standard Time Format

• B_R - Magnetic Field Vector Radial Component in Units of nT

• B_THETA - Magnetic Field Vector Theta Component, in Units of nT

• B_PHI - Magnetic Field Vector Phi Component, in Units of nT

The Vector Magnetic Field is rendered in a planetocentric right-handed Spherical Coordinate System in which the Angles Theta and Phi are the usual Polar Angles, with Theta (colatitude) measured from the Axis of Rotation and Phi increasing in the Direction of Rotation. The Orientation of the Pole of Neptune is specified by a Right Ascension of 298.90$#176; and Declination of 42.84$#176; at the Time of the Encounter, as given in the Jet Propulsion Laboratory Distribution of Physical Constants dated 11/06/89. Planetary Longitudes are based on a 16.11 h Rotation Period (Warwick et al., 1989) adopted by the Voyager Project shortly after the Encounter. The Zero Longitude is defined by the Requirement that the west Longitude of the Spacecraft at 03:56 SCET on Day 237 (near Closest Approach) be 167.7°. West Longitude in the Neptune Longitude System (NLS) are simply related to the Angle Phi by:

WLONG=360.0-PHI in degrees