| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set consists of magnetic field vector data recorded by
the Fluxgate Magnetometer on board the Pioneer 11 spacecraft,
during the Saturn encounter period. Data include 5 minute
averages of the magnetic field in RK spherical coordinates
and spacecraft trajectory in Kronographic (L1) coordinates.
Data Sampling
==============
At Saturn, instantaneous vector measurements were obtained
every 146.3 second, in synchronism with the spacecraft spin
period of 7.7 second.
The NSSDC documentation does not contain information about what
data resolution this data set (5 minute) is averaged from.
The time resolution for this data set is described as 5 minute
in the NSSDC documentation. However, data point spacing in the
file is variable and found mostly about 7 minute.
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 Saturn encounter were
originally written on an ASCII magnetic tape created on the
MODCOMP IV computer from card images. The original file was
re-formatted into a new ASCII file named P11_FGM_SAT_ENC_5MIN.TAB
which contains the following data columns:
--------------------------------------------------------------------
Column Column Column
Name Format Description
--------------------------------------------------------------------
TIME A24 Time in yyyy-mm-ddThh:mm:ss.sssZ
R F6.3 Distance of Pioneer 11 from Saturn in Rs
LAT F7.2 Latitude of Pioneer 11 in L1 coordinates
LON F8.3 Longitude of Pioneer 11 in L1 coordinates
BR F9.5 Radial component of the magnetic field in
RK coordinates
BTHETA F9.5 Polar component of the magnetic field in
RK coordinates
BPHI F9.5 Azimuthal component of the magnetic field in
RK coordinates
--------------------------------------------------------------------
Coordinate System for Data
===========================
Kronographic (L1) coordinates is a Saturn centered spherical
system, based on the Saturn Longitude System (Voyager Measurements
of the Rotation Period of Saturn's Magnetic Field, Desch and Kaiser,
JGR, 8, 253, 1981).
RK coordinates is based on two principle directions, Saturn to
Pioneer 11, R, and Saturn spin axis, J. X=R points away from
Saturn. Y is a vector in the direction of J cross R. Z is X
cross Y. Radial direction R, points away from Saturn, polar
direction THETA, positive northward, and azimuthal direction,
PSI, parallel to the X-Y plane, positive eastward.
Ancillary Data
==============
There is no ancillary data associated with this data set.
Instrument Calibration
======================
The fluxgate magnetometer was calibrated at the GSFC Magnetic
Test Facility by means of a 2 meter diameter, single axis
Helmholtz coil system. Typically hysteresis observed after
exposure to 2.5 mT fields was less than 1 part in 10**3 (one
count). Temperature stability is better than +- 0.5% over the
temperature range of -20 to +40 degree Celsius in spite of the
open loop design of the instrument. This is due to the fact
that the characteristics of the magnetic material used in the
sensor cores are fairly independent of temperature over the
indicated range. The stability figure includes the A/D converter
drift and a large portion of it is due to the single ramp design
of the latter. Nevertheless, minimum power consumption
requirements and flight qualified component availability
precluded the used of more stable A/D converter designs
(ACUNA&NESS1974).
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