PDS_VERSION_ID = PDS3
LABEL_REVISION_NOTE = "
2016-05-15 JNO:lawton V01;
2016-08-18 JNO:lawton;
2016-11-08 JNO:lawton;
2018-08-02, D. Kazden (PPI), removed ARCHIVE_STATUS keyword;
2019-12-02, PPI:mafi, updated CITATION_DESC;
"
RECORD_TYPE = STREAM
OBJECT = DATA_SET
DATA_SET_ID = "JNO-SS-3-FGM-CAL-V1.0"
OBJECT = DATA_SET_INFORMATION
DATA_SET_NAME = "JUNO SS FLUXGATE MAGNETOMETER
CALIBRATED DATA V1.0"
DATA_SET_COLLECTION_MEMBER_FLG = "N"
DATA_OBJECT_TYPE = TABLE
START_TIME = 2011-235T15:06:11
STOP_TIME = 2016-181T23:59:59
DATA_SET_RELEASE_DATE = 2016-11-09
PRODUCER_FULL_NAME = "JOHN CONNERNEY"
DETAILED_CATALOG_FLAG = "N"
CITATION_DESC = "Connerney, J.E.P., Juno MAG CALIBRATED
DATA SS V1.0, JNO-SS-3-FGM-CAL-V1.0, NASA Planetary Data System, 2016"
DATA_SET_TERSE_DESC = "The Juno Fluxgate Magnetomer (FGM)
calibrated observations consist of time and position tagged magnetic
field samples in physical units and coordinate systems collected by the
FGM instrument during cruise."
ABSTRACT_DESC = "
Abstract
========
This data set consists of the Juno FGM calibrated cruise observations.
The FGM sensor block uses two miniature ring-core fluxgate sensors to
measure the magnetic field in three components of the vector field.
There are multiple FGM data products to accomodate different
coordinate systems."
DATA_SET_DESC = "
Data Set Overview
=================
The data set consists of calibrated observations. The MAG measures
the vector magnetic field.
There are two principal coordinate systems used to represent the data
in this archive. The payload (pl) coordinate system and the SE
coordinate system is a Spacecraft-Solar equatorial system. The
sun-state (ss) and planetocentric (pc) will also be used for Earth Fly
By (EFB) and days 2016-177 through 181 Jupiter approach data. Cartesian
representations are used for all four coordinate systems. The se, pc,
and ss coordinate systems are specified relative to a 'target body'
which may be any solar system object. Primarily the 'target body' is
Jupiter, but for EFB it is Earth. In what follows we will reference
Jupiter as the target body, but, for example, if observations near a
satellite (such as Io) are desired in Io-centric coordinates, the
satellite Io may be specified as the target body.
The SE coordinate system is defined using the sun-spacecraft vector
as the primary reference vector; sun's rotation axis as the secondary
reference vector (z). The x axis lies along the sun-spacecraft
vector, the z axis is in the plane defined by the Sun's rotation axis
and the spacecraft-sun vector. The y axis completes the system.
The ss coordinate system is defined using the instantaneous Jupiter-Sun
vector as the primary reference vector (x direction). The X-axis lies
along this vector and is taken to be positive toward the Sun. The
Jupiter orbital velocity vector is the second vector used to define
the coordinate system; the y axis lies in the plane determined by the
Jupiter-Sun vector and the velocity vector and is orthogonal to the x
axis (very nearly the negative of the velocity vector). The vector
cross product of x and y yields a vector z parallel to the northward
(upward) normal of the orbit plane of Jupiter. This system is sometimes
called a sun-state (ss) coordinate system since its principal vectors
are the Sun vector and the Jupiter state vector.
The planetocentric (pc) coordinate system is body-fixed and rotates
with the body as it spins on its axis. The body rotation axis is the
primary vector used to define this coordinate system. Z is taken to
lie along the rotation axis and be positive in the direction of
positive angular momentum. The X-axis is defined to lie in the
equatorial plane of the body, perpendicular to Z, and in the direction
of the prime meridian as defined by the IAU. The Y axis completes the
right-handed set.
Data in the vicinity of the moons of Jupiter (Io, Europa, Ganymede,
Callisto) may be provided in separate files in moon centered coordinate
systems, if it turns out that the mission plan affords an opportunity
to acquire data in the immediate vicinity of any of these bodies The
planetocentric and SS data follows the definitions above with the
reference body being the moon or target specified via option in the
command line All of the archived data files are simple and readable
ASCII files with attached documentation in a header that precedes the
columns of data. Files using a coordinate system centered on a target
body other than Jupiter are identified via the target body listed on
the command line which appears in the header along with an audit trail
of supplementary engineering (kernel) files.
The output from the processing program is in Standard Time Series (STS)
format. The Object Description Language (odl) header is included in the
STS file. There will also be a detached PDS label file describing the
contents of the STS file.
Each data file contains the observations collected on a given UTC day.
Instrument Overview
===================
Please see JNO_FGM_INST.CAT.
Parameters
==========
The FGM powers up in operational mode and returns telemetry
immediately every clock tic (2 seconds). The FGM may be operated
in autoranging mode, or manual range commands may be sent to fix
the instrument in any of its dynamic ranges. Likewise any telemetry
mode may be selected, depending on telemetry resource allocation. In
addition, packets of engineering telemetry (in addition to science
telemetry packets) are telemetered at a variable rate, from one per
2 seconds to one per 512 seconds, per commanded state.
Calibration Overview
====================
The FGMs were calibrated in the Planetary Magnetospheres Laboratory
and the GSFC Mario H. Acuna (MHA) Magnetic Test Facility (MTF), a
remote facility located near the GSFC campus. These facilities are
sufficient to calibrate the FGMs to 100 parts per million (ppm)
absolute vector accuracy. An independent measurement of the magnetic
field strength in the 0.25, 1, and 4 Gauss ranges was provided by
Overhausen Proton Precession magnetometers placed near the FGM. Scale
factor calibration is extended to 16 Gauss using a specialized high
field coil and measurement techniques (see JUNO Magnetic Field
Investigation instrument paper). A nuclear magnetic resonance
magnetometer (Virginia Scientific Instruments) provided the absolute
field strength measurements in the 16 Gauss range.
Two independent methods are used to calibrate the magnetometers. The
vector fluxgates are calibrated in the 22' facility using a method
('MAGSAT method') developed by Mario Acuna and others. This technique
uses precise 90 degree rotations of the sensing element and a sequence
of applied fields to simultaneously determine the magnetometer
instrument model response parameters (the 'A matrix') as well as a
similar set of parameters (the 'B matrix') that describe the facility
coil orthogonality [instrument paper reference]. The second calibration
method (called the 'thin shell' and 'thick shell') uses a large set of
rotations in a known field (magnitude) to obtain the same instrument
parameters, subject to an arbitrary rotation [Merayo 2000 & 2001]. In
the 'thin shell' method, the sensor is articulated through all
orientations in a fixed, or known field magnitude. This can be done in
a facility like the GSFC 22 foot coil system, wherein any fixed field
up to about 1.2 Gauss may be utilized, or it may be done in the Earth's
field using the ambient field in a gradient-free region and a system
to compensate for variations in the ambient field (normally corrected
via a secondary reference magnetometer coupled with a Proton Precession
total field instrument). Application of this method in a coil facility
(with closed loop control for ambient field variations) allows for the
'thin shell' to be performed at many field magnitudes ('thick shell').
The MAGSAT calibration method provides the instrument calibration
parameters referenced to the optical cube mounted on the sensor
(or MOB) which defines the instrument coordinate system. These
parameters include the instrument scale factors, 3 by 3 instrument
response matrix (or 'A' matrix), and zero offsets for each instrument
dynamic range. The 'thin shell' method provides the same parameters,
but since the method conveys no attitude information, only the
symmetric part of the instrument response matrix is determined via
'thin shell'. Nevertheless, it provides a useful independent verification
of the MAGSAT calibration.
Inflight calibration activities are designed to monitor instrument
parameters, primarily zero offsets, and to monitor the relative
alignment of the magnetic field sensor platforms (the MOBs) and the
spacecraft attitude reference (Stellar Reference Units, or SRUs).
Spacecraft generated magnetic fields will be monitored using the dual
magnetometer technique and a series of magnetic compatibility tests
designed to identify the source of any magnetic signals (if any)
associated with spacecraft payloads. Since Juno is a spinning
spacecraft, spinning at 1 or 2 rpm nominally, any field fixed in the
frame of reference of the spacecraft (e.g., fixed spacecraft-generated
magnetic fields, sensor offsets, etc.) is easily identified. In practice
we apply an algorithm developed independently by several groups (Acuna,
Reviews of Scientific Instruments, 2002) to estimate bias offsets using
differences in the measured field. This method handily corrects for
biases in the spacecraft x and y axes, but since the spacecraft spins
about the z axis, biases in z must be estimated using different methods.
One technique utilizes the Alfvenic nature of fluctuations in the solar
wind, that is, the magnitude preserving nature of variations in the
field. Of course, not all fluctuations are Alfvenic (preserving
magnitude) so some care is taken in application of this method to select
appropriate events.
Coordinate Systems
==================
The MAG data are represented in the following coordinate systems:
- spacecraft-solar equatorial
- spacecraft payload
- planetocentric
- sun-state
all described above.
Data
====
Data products contain the observations collected on a given
UTC day. Each coordinate system in a separate file."
CONFIDENCE_LEVEL_NOTE = "
Confidence Level Overview
=========================
Not applicable.
Review
======
The FGM data set was reviewed internally by the MAG team prior to
release to the PDS. PDS also performed an external review of the MAG
data.
Limitations
===========
The Juno magnetic field investigation was designed to measure fields
to 16 Gauss per axis over 6 dynamic ranges of the instrument, the most
sensitive of which is +/- 1600 nT with a quantization step size of
0.05 nT (16 bit A/D). Moreover, the spacecraft magnetic requirement was
not to exceed 2 nT static and 0.5 nT variable spacecraft-generated
magnetic field. In very weak field environments, such as encountered in
outer cruise, accuracy may be expected to be limited by sensor offset
and spacecraft magnetic field variations. The combined (static)
spacecraft-generated magnetic field and sensor offset may be continuously
monitored in flight in the spacecraft x and y axis, since the spacecraft
spins (nominally at 1 or 2 RPM) about an axis closely aligned with the
spacecraft payload z axis. However, offsets in the z axis need be
estimated using the Alfvenic properties in the solar wind (ref. Juno
Magnetic field investigation paper in Space Science Reviews). Statistical
in nature, estimates of z axis zeros are not continuously available and
are less accurate than the x and y zeros. Also, variations in spacecraft
field over a time span comparable to a spin period will also lead to
larger errors."
END_OBJECT = DATA_SET_INFORMATION
OBJECT = DATA_SET_MISSION
MISSION_NAME = "JUNO"
END_OBJECT = DATA_SET_MISSION
OBJECT = DATA_SET_TARGET
TARGET_NAME = {"SOLAR SYSTEM",
"EARTH",
"JUPITER"}
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_HOST
INSTRUMENT_HOST_ID = JNO
INSTRUMENT_ID = "FGM"
END_OBJECT = DATA_SET_HOST
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = "CONNERNEYETAL2016"
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
END_OBJECT = DATA_SET
END
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