Data Set Information
|
DATA_SET_NAME |
GALILEO ORBITER EARTH MAG RDR EARTH2 HIGHRES V1.0
|
DATA_SET_ID |
GO-E-MAG-3-RDR-EARTH2-HIGHRES-V1.0
|
NSSDC_DATA_SET_ID |
|
DATA_SET_TERSE_DESCRIPTION |
Galileo Orbiter Magnetometer (MAG) calibrated
high-resolution data from the Earth-2 flyby in
spacecraft, GSE, and GSM coordinates. These data
cover the interval 1992-11-03 to 1992-12-19.
|
DATA_SET_DESCRIPTION |
Data Set Overview
=================
This dataset contains data acquired by the Galileo Magnetometer
from the Earth 2 encounter. The data are at the full instrument
resolution for the 7.68 kB Low Rate Science (LRS) real time
telemetry mode.
The data are provided in three coordinate systems: despun
spacecraft or inertial rotor coordinates (IRC), Geocentric Solar
Ecliptic (GSE) and Geocentric Solar Magnetic (GSM). The IRC
coordinate data files also include many of the data processing
parameters from the AACS system as well as the sensor zero levels.
These data have been fully processed to remove instrument response
function characteristics and interference from magnetic sources
aboard the spacecraft. The data are provided in physical units
(nanoTesla).
Processing
==========
These data have been processed from the PDS dataset:
'GO-E/V/A-MAG-2-RDR-RAWDATA-HIRES-V1.0'
The 'raw data' product was created from the EDR dataset by
removing the data processing done by the instrument in space. The
raw data dataset contains the raw instrument samples which have
been recursively filtered and decimated. In order to generate the
IRC processed data, the following procedure was followed:
1) Sensor zero level corrections were subtracted from the raw
data,
2) Data were converted to nanoTesla,
3) A coupling matrix which orthogonalizes the data and corrects
for gains was applied to the data (calibration applied),
4) Magnetic sources associated with the spacecraft were
subtracted from the data,
5) Data were 'despun' into inertial rotor coordinates,
For a more detailed description of these proceedures please refer
to the file /CALIB/HR_PROC.TXT. For more information regarding
data calibration please refer to [KEPKOETAL1996].
Parameters
==========
Data Sampling:
The Galileo magnetometer samples the magnetic field 30 times per
second. These highest rate samples are recursively filtered and
then resampled by the instrument at 4.5 vectors per second using a
7,7,6 decimation pattern.
Recursive Filter:
B(t) = 1/4 Bs(t) + 3/4 B(t-1)
B = output field
Bs = input field measured by the sensor
t = sample time
The pattern is generated by doubling the spacecraft clock modulo
10 counter and then applying the decimation scheme. This gives 3
vectors every spacecraft minor frame (about 2/3 second) which are
sampled unevenly. The first vector in a minor frame is sampled
approximately 0.200 seconds after the last vector in the preceding
minor frame. The other two samples are taken approximately 0.233
seconds apart. The time tag associated with a sample is the
decimation time.
Data Acquisition:
The data for this dataset were acquired as part of the normal
instrument calibration activities associated with the cruise to
Jupiter. As such, the instrument was commonly configured in modes
which required calibration even though they may not have been the
optimal mode for science data acquisition. The Galileo
magnetometer has 8 possible LRS acquisition configurations
(modes). There are two sensor triads mounted 7 and 11 meters from
the rotor spin axis (inboard and outboard) along the boom. Each of
the sensor triads has two gain states (high and low). In addition,
the sensor triads can be 'flipped' to move the spacecraft
spin-axis aligned sensor into the spin plane and visa versa.
Please see the instrument description (/CATALOG/MAGINST.CAT) for
full details on the instrument, sensors, and geometries. The
combinations of sensor, gain state, and flip direction form modes.
------------------------------------------------------------------
Table 1. Mode Characteristics
------------------------------------------------------------------
Mode Name Acronym range quantization
------------------------------------------------------------------
Inboard, left, high range* ILHR +/- 16384 nT 8.0 nT
Inboard, right, high range* IRHR +/- 16384 nT 8.0 nT
Inboard, left, low range* ILLR +/- 512 nT 0.25 nT
Inboard, right, low range* IRLR +/- 512 nT 0.25 nT
Outboard, left, high range* ULHR +/- 512 nT 0.25 nT
Outboard, right, high range* URHR +/- 512 nT 0.25 nT
Outboard, left, low range* ULLR +/- 32 nT 0.008 nT
Outboard, right, low range* URLR +/- 32 nT 0.008 nT
------------------------------------------
Table 2. Mode Change History
------------------------------------------
s/c clock date/time mode
------------------------------------------
00562976:00:0 90-305/16:31 ULHR
00572976:00:0 90-316/17:00 ULLR
00578673:00:0 90-320/17:00 URLR
00586204:00:0 90-325/23:55 URHR
00592915:00:0 90-330/17:01 ILLR
00597439:00:0 90-333/21:15 IRLR
00610156:00:0 90-342/19:33 IRHR
00610509:00:0 90-343/01:30 IRLR
00615701:00:0 90-346/17:00 URLR
00618550:00:0 90-348/17:00 URHR
00624261:00:0 90-352/17:15 ULHR
* range is the opposite of gain
In addition to exercising the various instrument modes during the
first earth encounter, numerous instrument calibration activities
were performed. These include using both the internal and external
calibration coils. Data corrupted by the use of the calibration
coils or by the flipper motor have been removed from the processed
data. These data have been archived with the Experimenter Data
Records (EDR) and other Magnetometer team raw data archive
products.
Data
====
The data are provided in three (3) coordinate systems (IRC, GSE,
and GSM). Data from the two geophysical coordinate systems are
stored in a single file. The IRC data are stored in a separate
file, and include some of the AACS and sensor offset parameters
which were used in processing the data. The structure and contents
of the data files are described below. The coordinate systems are
described later in this document in the section entitled
'Coordinate Systems.'
Data file structures:
------------------------------------------------------------------
Table 3. Data record structure, IRC Coordinates Data Files
------------------------------------------------------------------
Column Type Description
------------------------------------------------------------------
time char Spacecraft event time, PDS time format
sclk char Spacecraft clock (rim:mod91:mod10:mod8)
Bx_sc float B-field X component in S/C (IRC) coordinates
By_sc float B-field Y component in S/C (IRC) coordinates
Bz_sc float B-field Z component in S/C (IRC) coordinates
Bmag float |B| Magnitude of B
o1 float Offset subtracted from sensor1
o2 float Offset subtracted from sensor2
o3 float Offset subtracted from sensor3
rotattd float Rotor attitude declination (EME-50)
rotattr float Rotor attitude right ascension (EME-50)
rotattt float Rotor twist angle (EME-50)
spinangl float Rotor spin angle - inertial S/C coordinates
spindelt float Rotor spin motion delta
screlclk float Rotor-Platform relative clock angle
screlcon float Rotor-Platform relative cone angle
dqf float Data quality flag (see 'CONFIDENCE_LEVEL_NOTE'
for more details)
------------------------------------------------------------------
Table 4. Data record structure, GSE/GSM Coordinates Data Files
------------------------------------------------------------------
Column Type Description
------------------------------------------------------------------
time char Spacecraft event time, PDS time format
Bx float B-field X component in GSE or GSM coords.
By_gse float B-field Y component in GSE coordinates
Bz_gse float B-field Z component in GSE coordinates
By_gsm float B-field Y component in GSM coordinates
Bz_gsm float B-field Z component in GSM coordinates
Bmag float |B| Magnitude of B
Ancillary Data
==============
Trajectory data for GSE and GSM coordinates are provided
separately as part of the GO-E-POS-4-SUMM-E2-GSE/GSM-COORDS-V1.0
data set.
Coordinate Systems
==================
The data are provided in three coordinate systems. Data are
provided in the spacecraft coordinate system in order to aid in
the interpretation of particle instrument data. The other two
coordinate systems provided for use in Earth magnetospheric
studies.
The IRC coordinate system takes the basic rotor coordinate system
(Y along the boom, Z opposing the high gain antenna) which is
spinning, and despins by using the rotor spin angle. In this
system, Z still points roughly away from the Earth (with about
+/- 10 degree accuracy) along the rotor spin axis, X is
approximately parallel to the downward ecliptic normal, and Y
completes the right-handed set.
Geocentric Solar Ecliptic (GSE) and Geocentric Solar Magnetic
(GSM) are related earth centered coordinate systems. Both the GSE
and GSM X directions are taken along the Earth - Sun line,
positive towards the Sun. The GSE Z direction is parallel to the
ecliptic normal, positive northward, and Y completes the
right-handed set (towards dusk). For GSM, the X-Z plane contains
the Earth's dipole moment vector, positive northward, and Y
completes the right-handed set. GSE coordinates are commonly used
for analyzing the solar wind near the Earth and GSM coordinates
are used when analyzing data inside the Earth's bow shock.
|
DATA_SET_RELEASE_DATE |
2003-03-01T00:00:00.000Z
|
START_TIME |
1992-11-03T12:48:11.315Z
|
STOP_TIME |
1992-12-19T02:39:51.910Z
|
MISSION_NAME |
GALILEO
|
MISSION_START_DATE |
1977-10-01T12:00:00.000Z
|
MISSION_STOP_DATE |
2003-09-21T12:00:00.000Z
|
TARGET_NAME |
EARTH
|
TARGET_TYPE |
PLANET
|
INSTRUMENT_HOST_ID |
GO
|
INSTRUMENT_NAME |
TRIAXIAL FLUXGATE MAGNETOMETER
|
INSTRUMENT_ID |
MAG
|
INSTRUMENT_TYPE |
MAGNETOMETER
|
NODE_NAME |
Planetary Plasma Interactions
|
ARCHIVE_STATUS |
ARCHIVED
|
CONFIDENCE_LEVEL_NOTE |
Review
======
These data have been reviewed by the instrument team and are of
the highest quality that can be generated at this time. Science
results based on some of these data have been published in several
journals (Science, JGR, etc.). After submission to PDS, these data
successfully completed the peer review process.
Confidence Level Overview
=========================
Each aspect of the data processing sequence can be analyzed to
determine its maximum possible error contribution. In theory,
these errors could be summed to provide estimates of the maximum
error for each data point. Error analysis for these data have not
been taken to that level.
The MAG team believes that calibrations (sensor geometry and
gains) are good enough that they produce a negligible source of
data error. In addition, that the coordinate system
transformations which are derived from the SPICE kernels and
Toolkit are believed to be negligible sources of error in the
magnetic field vectors. The most significant sources of error are
those associated with magnetic sources aboard the spacecraft,
especially those with temporal or spacecraft orientation
variations. The next greatest contributor of error is the data
from the AACS which affects our knowledge of the spacecraft
orientation and hence rotates the magnetic field vector. Lastly,
telemetry or software errors which produce 'spikes' or bit errors
in the data are error sources.
Data Coverage and Quality
=========================
In regions where the magnetic sources associated with the
spacecraft are fairly constant, magnetic interference is probably
reduced by data processing to better than 0.05 nT at the inboard
sensors. In these same regions, sensor zero levels (offsets) are
known equally well. The data processing software does a fairly
good job of removing all currently identified sources of magnetic
interference. However, there are some time intervals when the zero
levels of the spin plane sensors show large variations (1-5 nT) on
short time scales (minutes to hours). After a while (hours to
days) the offsets return to their nominal levels. The source of
these magnetic fields has not yet been identified. The method of
removing offsets from the spin plane sensors does remove these
effects, but the method of determining the spin axis aligned
sensor offsets does not. In regions where large variations are
detected in the spin plane sensors it is reasonable to assume that
similar variations are taking place in the spin axis aligned
sensor.
A second problem in determining and removing the magnetic
interference associated with the spacecraft is the movement of
these magnetic sources. At the Earth 2 encounter an extensive test
was done to determine the interference patterns as a function of
the position of the magnetic sources. Data was taken with the scan
platform at fifteen degree intervals and the interference was
successfully modeled.
------------------------------------------------------------------
Table 5. Intervals Corrupted by Interference (Earth 2)
------------------------------------------------------------------
Time interval frequencies Amplitude of the
interference
remaining in |B|(nT)
------------------------------------------------------------------
Limitations
===========
MAG data processing software creates a data quality flag (DQF)
which is an assessment of AACS and telemetry error source
contamination of a given data point. This number is binary integer
where each bit indicates the presence or absence of some error
source. The number 0 represents the absence of all error sources
which are tested. The higher order bit (larger number) error
sources are considered to be more significant error sources. Data
are examined for gradients in the field which might be associated
with telemetry bit errors, for regions of bad AACS angles, and
for completely missing data. If the error is considered completely
unrecoverable, the data values are replaced with a missing data
flag. In the case of a flag in the rotor spin angle, the vector
components may be flagged but the magnitude is still valid. Here
is a list of all of the error checks and the bits they set in the
dqf field.
------------------------------------------------------------------
Table 6. Data Quality Flag (DQF) Values
------------------------------------------------------------------
DQF_GOOD_DATA 0 Good data
DQF_BX_GRAD_WARNING 2^0 Component gradient warning
DQF_BY_GRAD_WARNING 2^1 Component gradient warning
DQF_BZ_GRAD_WARNING 2^2 Component gradient warning
DQF_INTERP_ROTATTR 2^3 Missing rotor RA interpolated
DQF_INTERP_ROTATTD 2^4 Missing rotor DEC interpolated
DQF_INTERP_SPINDELT 2^5 Missing rotor Spin Delta
interpolated
DQF_INTERP_SCRELCON 2^6 Missing Relative Cone angle
interpolated
DQF_INTERP_SCRELCLK 2^7 Missing Relative Clock angle
interpolated
DQF_INTERP_ROTATTT 2^8 Missing rotor Twist interpolated
DQF_INTERP_SPINANGL 2^9 Missing rotor Spin interpolated
DQF_ROTATTR_FLAG 2^10 Missing rotor RA flagged
DQF_ROTATTD_FLAG 2^11 Missing rotor DEC flagged
DQF_SPINDELT_FLAG 2^12 Missing rotor Spin Delta flagged
DQF_SCRELCON_FLAG 2^13 Missing Relative Cone angle
flagged
DQF_SCRELCLK_FLAG 2^14 Missing Relative Clock angle
flagged
DQF_ROTATTT_FLAG 2^15 Missing rotor Twist flagged
DQF_AACS_TELEMETRY_HIT_FLAG 2^16 Telemetry hit in AACS record
DQF_MAG_TELEMETRY_HIT_FLAG 2^17 Telemetry hit in mag record
DQF_SPINANGL_FLAG 2^18 Missing rotor Spin flagged
DQF_BX_GRAD_ERROR 2^25 Component gradient error
DQF_BY_GRAD_ERROR 2^26 Component gradient error
DQF_BZ_GRAD_ERROR 2^27 Component gradient error
DQF_BX_FLAG 2^28 Component flagged
DQF_BY_FLAG 2^29 Component flagged
DQF_BZ_FLAG 2^30 Component flagged
Magnetic field gradient warning or error levels are set during the
data processing according to expected variances depending on the
region of space. In the solar wind, gradient warnings are usually
issued at gradients of 10 nT/sec and errors at 15 nT/sec. In the
magnetosheath, these values may be 50 percent larger. In the inner
magnetosphere, these dqf flags may be completely turned off.
Similarly, AACS angles are interpolated across gaps during the
processing if the gap length is relatively short (less than 10
minutes typically). If the gaps in spacecraft attitude are long,
the AACS angles are flagged and not interpolated.
Errors associated with AACS angles have various effects on the
data. The rotor right ascension and declination are crucial to the
understanding of the spacecraft orientation. Fortunately, these
angles are slowly varying and can be interpolated to better than 1
degree of accuracy for long (many hour) time periods except near
major spacecraft maneuvers. The relative clock and cone angles are
used to remove scan platform interference. In their absence, no
interference is removed (+/- 0.15 nT error possible in each
component). The rotor motion spin delta is used to determine the
instantaneous spin frequency for the phase delay computation. In
its absence, the last known phase delay is applied to the current
data point. The rotor spin angle and twist angle must be present
in order to despin the data. These angles are generally not
interpolated for more than ten minutes because the rotor spin
period drifts over time periods on this order.
|
CITATION_DESCRIPTION |
Kivelson, M.G., Khurana, K.K., Russell, C.T., Walker, R.J.,
Joy, S.P.,Green, J., GALILEO ORBITER EARTH MAG RDR EARTH2
HIGHRES V1.0, GO-E-MAG-3-RDR-EARTH2-HIGHRES-V1.0, NASA
Planetary Data System, 2003
|
ABSTRACT_TEXT |
Galileo Orbiter Magnetometer (MAG) calibrated
high-resolution data from the Earth-2 flyby in
spacecraft, GSE, and GSM coordinates. These data
cover the interval 1992-11-03 to 1992-12-19.
|
PRODUCER_FULL_NAME |
MARGARET G. KIVELSON
|
SEARCH/ACCESS DATA |
Planetary Plasma Interactions Website
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