PDS_VERSION_ID = PDS3
LABEL_REVISION_NOTE = "
2001-11-05, S. Joy, initial draft;
2003-04-17, J. Mafi, major revision, tables added;
2003-06-25, S. Joy, minor revisions, targets added;
2003-08-18, S. Joy, minor revisions requested at peer review;
2004-08-02, J. Mafi, changes related to product version id 3;"
OBJECT = DATA_SET
DATA_SET_ID = "GO-J-MAG-3-RDR-MAGSPHERIC-SURVEY-V1.0"
OBJECT = DATA_SET_INFORMATION
DATA_SET_NAME = "
GO JUPITER MAG MAGNETOSPHERIC SURVEY V1.0"
DATA_SET_COLLECTION_MEMBER_FLG = N
START_TIME = 1995-11-06T00:21
STOP_TIME = 2003-09-21T18:00
DATA_SET_RELEASE_DATE = 1997-07-01
PRODUCER_FULL_NAME = "DR. MARGARET G. KIVELSON"
DETAILED_CATALOG_FLAG = Y
ARCHIVE_STATUS = "LOCALLY ARCHIVED"
DATA_OBJECT_TYPE = "TABLE"
CITATION_DESC = "Kivelson, M.G., Khurana, K.K.,
Russell, C.T., Walker, R.J., Joy, S.P., Mafi, J.N.,
GO JUPITER MAG MAGNETOSPHERIC SURVEY V1.0,
GO-J-MAG-3-RDR-MAGSPHERIC-SURVEY-V1.0, NASA Planetary Data System, 1997"
ABSTRACT_DESC = "
This data set contains magnetic field vectors acquired by the
Galileo Orbiter magnetometer during the magnetospheric survey
portion of the mission. These data were acquired in the optimal
averager (opt/avg) and real-time survey (RTS) modes beginning during
the Jupiter approach and continuing throughout Jupiter orbital
operations. The data set covers the time period from
1995-11-06T00:21:30 UT (Jupiter approach) until the end of mission
(September 2003). Sampling rates are variable and depended upon the
downlink capabilities. With few exceptions, the data are provided at
the full downlink resolution. The data are provided in five
coordinate systems (IRC, System III [1965], JSE, JSO, and JSM)."
DATA_SET_TERSE_DESC = "
Galileo Magnetometer data and browse plots from the Jovian
magnetospheric survey for all orbits and satellite flybys (Io, Europa,
Ganymede, Callisto, and Amalthea)."
DATA_SET_DESC = "
Data Set Overview
=================
This data set contains magnetic field vectors acquired by the
Galileo Orbiter magnetometer during the magnetospheric survey
portion of the mission. These data were acquired in the optimal
averager (opt/avg) and real-time survey (RTS) modes beginning during
the Jupiter approach and continuing throughout Jupiter orbital
operations. The data set covers the time period from
1995-11-06T00:21:30 UT (Jupiter approach) until the end of mission
(September 2003). Sampling rates are variable and depended upon the
downlink capabilities. With few exceptions, the data are provided at
the full downlink resolution. The data are provided in five
coordinate systems (IRC, System III [1965], JSE, JSO, and JSM).
Parameters
==========
Data Sampling
-------------
Data acquisition strategies varied throughout the mission. During
the Jupiter approach period, most particles and fields (MWG)
instruments were off while the magnetometer acquired low
resolution opt/avg data. During the bulk of the prime mission,
the MWG instruments were allowed to acquire continuous RTS data
whenever the spacecraft was inside 50 Jovian radii (Rj). When the
MWG was not returning RTS data, MAG used its opt/avg capability to
acquire low time resolution averages of the field. In general,
these are ~32 minute averages, although some higher rate data (1-8
minute) were used to fill small gaps in RTS data coverage. Early
in the prime mission, MAG was required to 'pay' for the bits its
used to return the opt/avg data by not acquiring as much high
resolution data. MAG did not return data from the MWG transauroral
crossing recorded interval in the C3 orbit so that it could have
continuous coverage during that orbit. After the fourth orbit, the
MAG opt/avg data was return in the spacecraft engineering data
stream at no cost to the team. The MWG acquired RTS data beyond
50 Rj in selected bit rich orbits (G2, G7, G8, C9, C10) during the
prime mission.
RTS, opt/avg, and snapshot data were all stored in the MAG
internal memory buffer. RTS data were continuously averaged at MAG
memory address 4800 and transmitted to Earth in real-time. When an
opt/avg ON command was given data were stored in the MAG memory
buffer beginning at address 4800 and continuing to higher
addresses until Opt/Avg OFF was commanded, another Opt/Avg ON was
commanded and the MAG buffer began filling at 4800 again, or the
MAG memory buffer filled. Opt/avg data was returned to Earth via
Memory Read-Out (MRO) as telemetry permitted. Since RTS and
opt/avg data used the MAG memory buffer in different ways, they
could not be collected simultaneously. Snapshot data, which
completely filled the MAG memory buffer, could likewise not be
collected simultaneously with opt/avg, and caused periodic spikes
in RTS data. Snapshot corruption of RTS data is discussed in more
detail in the 'Data Quality and Coverage' section of this
document. For a more detailed discussion how MAG RTS, opt/avg, and
snapshot data are collected, please refer to [KIVELSONETAL1992].
When high-resolution data were available, but the RTS data were
either lost or corrupted, simulated RTS (sRTS) data have been
generated from the high-resolution data. sRTS data were averaged
down to the RTS rate, then interpolated to be continuous with the
existing RTS data.
During the prime mission, the RTS data rate varied, depending the
downlink capability. MAG has several different possible
RTS data rates depending on the telemetry format:
---------------------------------------------------------------------
Table 1. MAG RTS Rates
---------------------------------------------------------------------
Format MAG bit rate Time between samples Corner Freq.
(bps) (seconds) (mf) (Hz)
---------------------------------------------------------------------
A-D 2 24 36 1/34
E 4 12 18 1/34
F 6 8 12 1/17
G 8 6 9 1/17
H 12 4 6 1/17
I 18 8/3 4 1/17
Similarly, the opt/avg data can be acquired at different rates.
The relatively high data rates fill the MAG internal memory buffer
more quickly and are only used to cover short data disruptions.
---------------------------------------------------------------------
Table 2. Optimal Averager Data Rates
---------------------------------------------------------------------
Time between samples Buffer fill time Corner Freq.
(RIM) (hh:mm:ss.ss) (day/hh:mm) (Hz)
---------------------------------------------------------------------
1 00:01:00.67 03:22 1/67
2 00:02:01.33 06:44 1/134
4 00:04:02.67 13:29 1/268
8 00:08:05.33 1/02:58 1/536
16 00:16:10.67 2/05:56 1/1072
32 00:32:21.33 4/11:51 1/2144
64 01:04:42.67 8/23:42 1/4289
The instrument has the ability to acquire longer time averages
but these modes were not used at Jupiter.
After the prime mission ended (December 1997), RTS data
acquisition was limited to only a few days near perijove except
for a few orbits. RTS data are typically in the 2 bps (24
sec/sample) telemetry formats. Opt/avg data after end of the
prime mission, are primarily provided in 32 RIM (~32 min/sample)
averages.
Both the opt/avg and the RTS data processor compute field averages
by applying a recursive filter and decimate algorithm to the data.
The instrument applies a calibration, decimates vectors down to
minor frame (mf) samples (2/3 second) and despins the data using
the spin angle value broadcast on the spacecraft bus. The corner
frequencies of the recursive filter are provided in tables 1 and 2
for the various sample durations. The effect of this process is
that the spacecraft time tags both RTS and opt/avg data at the
time of decimation (end of average), rather than at the effective
'center' of the average. As a result there is a time shift or
phase delay between RTS or opt/avg data and data (e.g. LPW) which
have not undergone the same filtering process. The magnitude of
the phase delay is dependent upon the averaging interval (or
rate) and frequency content of the data. Analysis of the filter
response to a wave at the spin period (dominant frequency) has
determined that the phase delay may be eliminated with the
correction:
[Corrected time] = [Sample time] - (Rate * (1/3))
Where the 'Sample time' is the time assigned by the spacecraft,
and the 'Rate' is the sampling rate in seconds. Both 'Sample Time'
and 'Corrected Time' are provided in the data files. The IRC data
file (which does not include a 'Corrected Time' column) contains
a 'Spacecraft Clock' column which corresponds to the 'Sample Time'
(and not the 'Corrected Time'). The RTS and opt/avg data overlay
high time resolution data acquired at the same time best when the
'Corrected Time' is used.
MAG uses fixed gains to acquire data [KIVELSONETAL1992]. Gain
states must be manually changed by sending a gain change
command to the instrument. There are 3 ranges of field strengths
that the instrument can measure:
---------------------------------------------------------------------
Table 3. Magnetometer Ranges
---------------------------------------------------------------------
Field Range (nT) Magnetometer, range
min max
---------------------------------------------------------------------
1/64 - 32 Outboard low field
1/4 - 512 Outboard high field, Inboard low field
8 - 16384 Inboard high field
While the outboard magnetometer's position on the boom does make
it less susceptible to spacecraft fields, its zero levels were
less stable than those of the inboard magnetometer. As a result,
the outboard magnetometer was generally not used except when the
magnetic field strength was very low. The outboard magnetometer
was typically only used outside of 60 Rj (in the low field
range). From 9-60 Rj the inboard magnetometer, low field range
was generally used. Inside of ~9 Rj the inboard magnetometer,
high field range was used.
Processing
==========
Browse data are primarily processed onboard the spacecraft by using
estimates of the instrument calibration and zero levels. The
calibration estimates cannot be improved in post processing due to
the onboard averaging. Any errors in the sensor zero levels in the
spin plane sensors will appear as harmonics of the spin period,
possibly modified by frequency folding effects associated with the
averaging windows. These effects can be removed in the RTS data in
post processing. The long average intervals of the opt/avg data
effectively removes these problems without need for post processing.
Improvements are made to the zero level correction of the spin
aligned sensor data for both RTS and opt/avg data in post
processing.
Data
====
These data are stored in multiple data files in order to facilitate
use and electronic distribution. In general, data from a single
orbit is included in a data file. For some of the more data rich
orbits, further subdivision was provided. Data from the five
coordinate systems are stored in four separate files. The file
format for a particular coordinate system is independent of the data
acquisition interval. All data files from a given coordinate system
are identical in structure. All data files are ASCII, fixed field,
white space delimited tables. The following tables (4a-d) describe
the record structure of the various type of data files.
--------------------------------------------------------------------
Table 4a. IRC Coordinates (Inertial Rotor coordinates)
--------------------------------------------------------------------
Column Type Description <units>
--------------------------------------------------------------------
samp time char spacecraft event time sample was acquired from
MAG memory, PDS time format
sclk char spacecraft clock (rim:mf:mod10:mod8)
Bx_sc float magnetic-field spacecraft (IRC) x-component <nT>
By_sc float magnetic-field spacecraft (IRC) y-component <nT>
Bz_sc float magnetic-field spacecraft (IRC) z-component <nT>
|B| float magnetic-field magnitude <nT>
rotattr float rotor right ascension <degrees>
rotattd float rotor declination <degrees>
rotattt float rotor spin phase (twist) angle <degrees>
spinangl float rotor spin phase angle <degrees>
RATE float data sample rate <seconds>
--------------------------------------------------------------------
Table 4b. System III [1965] Coordinates
--------------------------------------------------------------------
Column Type Description <units>
--------------------------------------------------------------------
corr time char spacecraft event time of sample corrected for
MAG filter response, PDS time format
samp time char spacecraft event time sample was acquired from
MAG memory, PDS time format
Br float magnetic-field R (radial) component <nT>
Btheta float magnetic-field theta (southward) component <nT>
Bphi float magnetic-field phi (eastward) component <nT>
|B| float magnetic-field magnitude <nT>
R float s/c position - Radial distance from Jupiter
center-of-mass <Rj = 71492 km>
LAT float s/c position - latitude <degrees>
ELON float s/c position - East longitude <degrees>
WLON float s/c position - West longitude <degrees>
--------------------------------------------------------------------
Table 4c. Jupiter Solar Equatorial (JSE) Coordinates
--------------------------------------------------------------------
Column Type Description <units>
--------------------------------------------------------------------
corr time char spacecraft event time of sample corrected for
MAG filter response, PDS time format
samp time char spacecraft event time sample was acquired from
MAG memory, PDS time format
Bx float magnetic-field x (sunward) component <nT>
By float magnetic-field y (duskward) component <nT>
Bz float magnetic-field z (Jovian spin axis aligned)
component <nT>
|B| float magnetic-field magnitude <nT>
X float s/c position - x (sunward) component <Rj>
Y float s/c position - y (duskward) component <Rj>
Z float s/c position - z (northward) component <Rj>
LOCHOUR float s/c local hour <hours>
--------------------------------------------------------------------
Table 4d. Jupiter Solar Orbital (JSO) and Jupiter Solar Magnetic
(JSM) Coordinates
--------------------------------------------------------------------
Column Type Description <units>
--------------------------------------------------------------------
corr time char spacecraft event time of sample corrected for
MAG filter response, PDS time format
samp time char spacecraft event time sample was acquired from
MAG memory, PDS time format
Bx float JSO/JSM magnetic-field x-component <nT>
By_jso float JSO magnetic-field y-component <nT>
Bz_jso float JSO magnetic-field z-component <nT>
By_jsm float JSM magnetic-field y-component <nT>
Bz_jsm float JSM magnetic-field z-component <nT>
|B| float magnetic-field magnitude <nT>
X float s/c position - JSO/JSM x-component <Rj>
Y_JSO float s/c position - JSO y-component <Rj>
Z_JSO float s/c position - JSO z-component <Rj>
Y_JSM float s/c position - JSM y-component <Rj>
Z_JSM float s/c position - JSM z-component <Rj>
MLOCHOUR float S/C magnetic local hour <hours>
These data were processed using SPICE kernels produced by the
Galileo NAV team during the mission. All of the SPICE kernels
used to produce this data set are contained on the MWG archive
volume DVD in the EXTRAS/SPICE/KERNELS directory.
The kernels (PDS PRODUCT_ID) used to create this were:
S980326B.TSP - Prime Mission Reconstruction (JA-E12)
S000131A.TSP - GEM reconstruction (E12-E26)
S030916A.TSP - GMM (I27-J35) reconstruction
PCK00007.TPC - Planetary constants kernel (2000-04-24)
MK00062B.TSC - Galileo spacecraft clock kernel
Coordinate Systems
==================
The data are provided in five coordinate systems. Data are provided
in the spacecraft coordinate system in order to aid in the
interpretation of particle instrument data. The other coordinate
systems are provided for use in Jovian magnetospheric studies. The
Jupiter spin axis is defined to have a right ascension of 268.05
degrees and a declination of +64.49 degrees in the J2000 coordinate
system used by SPICE.
Inertial Rotor Coordinates (IRC)
--------------------------------
The IRC coordinate system takes the basic rotor coordinate system
(Y along the boom, Z opposite the high gain antenna) which is
spinning, and despins it using the rotor spin angle. For this
reason IRC coordinates are sometimes referred to as 'despun
spacecraft coordinates.' In this system, Z still points along the
spin axis opposite the HGA (or roughly anti-Earthward), X is
approximately parallel to the downward ecliptic normal, and Y
completes the right handed set (pointing roughly towards dawn).
System III [1965] Coordinates (SYS3)
------------------------------------
SYS3 magnetic field vector components form the standard right
handed spherical triad (R, Theta, Phi) for a Jupiter centered
system. Namely, R is radial (along the line from the center of
Jupiter to the center of the spacecraft), and positive away from
Jupiter. Phi, the azimuthal component, is parallel to the
Jovigraphic equator (Omega x R) and positive in the direction of
corotation. Theta, the 'southward' component, completes the right
handed set.
For SYS3 trajectory both east and west longitudes are provided.
West longitudes are related to east longitudes by to the
algorithm:
west longitude = 360. - east longitude <degrees>
West longitude is defined such that it appears to increase with
time for a stationary observer [DESSLER1983]. Note, however, that
R, latitude, and west longitude constitute a left handed set. The
SYS3 1965 prime meridian is the sub-Earth longitude of
1965-01-01 00:00 UT. The spin rate (which was determined from the
rotation rate of the magnetic field) is 9 hrs 55 min 29.719 sec.
(See [DESSLER1983] for a discussion on Jovian longitude). R is the
radial (Jupiter's center to spacecraft center) distance. Latitude
is planetocentric.
Jupiter Solar Equatorial Coordinates (JSE)
------------------------------------------
JSE is a Jupiter centered cartesian coordinates system defined to
have it's Z-axis along the Jovian spin axis, positive in the
direction of angular momentum (northward). The X-Z plane is
contains the Sun so that the X-axis is the projection of the Sun
direction into Jupiter's equatorial plane (positive towards the
Sun). Y completes the right handed set and points duskward. This
coordinate system is sometimes called Jupiter centered, Sun
longitude fixed coordinates.
Jupiter Solar Orbital Coordinates (JSO)
---------------------------------------
JSO is another Jupiter centered cartesian coordinate system. JSO
is the equivalent at Jupiter of GSE coordinates system at Earth.
In JSO coordinates, the X-axis points from Jupiter to the Sun. Z
is parallel to the upward normal to Jupiter's orbital plane. Y
completes the right handed set.
Jupiter Solar Magnetic Coordinates (JSM)
----------------------------------------
Another Jupiter centered cartesian coordinate system, JSM is the
equivalent at Jupiter of GSM coordinates system at Earth. In this
coordinate system, the X-axis points from Jupiter to the Sun. The
secondary vector defining this coordinate system is the centered
magnetic dipole axis (M) which is defined to be tilted 9.6 degrees
from the Jovian spin axis towards 202 degrees SYS3 west longitude.
The X-Z plane is contains M. Y completes the right handed set. The
Y-Z plane rocks at the Jovian spin period about the Sun-Jupiter
line.
Local Hour
----------
Local hour angle is the angle (HA) between the observer's
(Galileo) sub-Jupiter meridian and the anti-sunward meridian,
measured in the Jovian equatorial plane in the direction of
planetary rotation. Local hour is the conversion of the local
hour angle into units of decimal hours using the conversion
factor of one hour to fifteen degrees of longitude. The following
diagram is a graphic representation of local hour.
Sun
^
|
noon Planetocentric
12:00 Equatorial Projection
|
|
|
| Jupiter
* * */
* | *
(dusk) 18:00 -----------*--|--*------------- 06:00 (dawn)
* |\ *
* * *
| \
| \
| \
|-HA--\
00:00 + Spacecraft
midnight
Magnetic Local Hour
-------------------
Magnetic local hour angle is the angle (MHA) between the
observer's dipole meridian and the anti-sunward meridian,
measured in the magnetic equatorial plane in the direction of
planetary rotation. Magnetic local hour is the conversion of the
magnetic local hour angle into units of decimal hours by using
the conversion factor that equates one hour to fifteen degrees of
longitude. The following diagram is a graphic representation of
magnetic local hour.
Sun
^
|
noon Dipole
12:00 Equatorial Projection
|
|
|
| Jupiter
* * */
* | *
(dusk) 18:00 -----------*--|--*------------- 06:00 (dawn)
* |\ *
* * *
| \
| \
| \
|-MHA-\
00:00 + Spacecraft
midnight
Ancillary Data
==============
There are several files that are provided in addition to the data
files themselves that may be of value to the user. These include a
detailed data gap listing (including reason for gap), a table of
important spacecraft and instrument events, a discussion of
instrument anomalies and resolutions, and a set of quick-look or
'browse' plots of the data.
References
==========
[DESSLER1983] Appendix B Coordinate Systems, in Physics of the
Jovian Magnetosphere, ed. Dessler, Cambridge Univ. Press,
New York, 1983.
[KIVELSONETAL1992] The Galileo Magnetic Field Investigation,
Space Science Rev. 60, 357, 1992.
[KIVELSONETAL1996A] A Magnetic Signature at Io: Initial Report from
the Galileo Magnetometer, Science, 273, 337, 1996
[KIVELSONETAL1996B] Io's interaction with the Plasma Torus, Science,
274, 396, 1996.
[KIVELSONETAL1997A] Galileo at Jupiter: Changing states of the
Magnetosphere and first looks at Io and Ganymede, Adv. Space
Res., 20, No 2, 193, 1997.
[HUDDLESTONETAL1998A] Location and Shape of the Jovian Magnetopause
and Bowshock, J. Geophys. Res, 103, no. E9, 20075, 1998."
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 these data have been published in several
journals (Science, Nature, JGR, etc.). After submission to the
PDS, these data successfully completed the peer review process.
Data Coverage and Quality
=========================
Gaps
----
The magnetometer browse data set contains all of the survey data
that were returned from the instrument. However, there are
numerous gaps in coverage. Gaps can be caused by telemetry
outages, insufficient downlink or uplink, conjunctions, instrument
anomalies, spacecraft anomalies, commanding errors, etc. A
detailed gap listing including a description of the reason for the
gap is provided in a separate file with these data. Here is a list
of some of the larger or more common gaps.
JA: Gaps in coverage due to limited telemetry
J0: Large gaps during probe relay and Io playback
G1: MAG flip/commanding anomaly (3.5 weeks); spacecraft safing
1 week)
J5: Conjunction, limited telemetry (5 weeks)
E6: Instrument anomaly, radiation hit (1.5 weeks)
G7: MAG flip anomaly (1 week)
E12: AACS anomaly (7 weeks)
J13: solar conjunction (6 weeks)
E14: spacecraft safing (5 days)
E15: ground station reallocated to SOHO for spacecraft anomaly
recovery effort (3 days)
E16: spacecraft safing (4 days)
E17: ground station reallocated to Voyager 2 for spacecraft
anomaly recovery effort (4 days)
E18: spacecraft safing (2 days); ground station reallocated to
NEAR for spacecraft anomaly recovery effort (2 days)
E19: spacecraft safing (1.5 weeks); solar conjunction (3 weeks)
I24: loss of telemetry during MRO (4 days)
I25: opt/avg corrupted by shapshots (2 days)
I27: spacecraft safing (2 days); solar conjunction (2.5 weeks)
G28: loss of telemetry during MRO (4 days)
G29: loss of telemetry during MRO (3 days)
C30: SSI anomaly recovery/loss of telemetry (2 days); solar
conjunction (2.5 weeks)
I33: spacecraft safing (1 week); loss of telemetry for MRO (2.5,
and 3 days); solar conjunction (3 weeks); loss of telemetry
during MRO (4 days); spacecraft safing (4.5 days)
A34: spacecraft safing (5 days); telemetry outage (4.5 days);
end of spacecraft operations before impact (36 weeks)
Other common causes of data gaps that are not related to
telemetry outages and anomaly gaps are listed below. Gaps may
have occurred throughout Jupiter Orbital Operations - whenever
the conditions which caused them existed.
Gaps between consecutive opt/avg segments: Gaps of at least two
data vectors occurred between consecutive opt/avg data segments.
The first and last vector in every opt/avg segment are
underfiltered and have therefore been discarded. For the most
common data opt/avg rate, this results in a gap of ~1 hour.
These gaps may be larger than two vectors if there is any delay
between the MRO of the data in the buffer and the subsequent
opt/avg ON command.
Snapshot corruption of RTS data: When snapshots (see
[KIVELSONETAL1992] for more information) were taken the
addresses in which RTS data were averaged were overwritten with
snapshot data. Since snapshots were written to MAG memory in
reversed byte order, the result was a spike which persisted over
the course of few records due to the application of the filter.
Whenever possible RTS data corrupted by snapshots have been
replaced with sRTS data which were unaffected by snapshots. When
high-resolution data are not available, however, snapshots
result in a series of short (3-6 vector), regularly spaced gaps
in the RTS.
The MAG data quality (size of error bars) varies with instrument
mode (digitization step size), sample rate, etc. The errors can
be broken down into three basic types: zero levels, gains, and
geometry.
Simulated RTS Data
------------------
While sRTS data have been matched to the existing RTS data rates
they have not been generated using the same process. sRTS data
have not gone through the same recursive filter that was applied
to the regular RTS data. sRTS has been generated for the following
intervals:
----------------------------------------------------
Table 5. Simulated RTS (sRTS) intervals
----------------------------------------------------
High-Res.
Orbit Obs. ID Start Time Stop Time
----------------------------------------------------
G1 G01-GAN 1996-06-27 06:07 1996-06-27 06:52
G1 G01-PSX 1996-06-30 02:01 1996-06-30 02:46
G2 G02-GAN 1996-09-06 18:33 1996-09-06 19:28
G2 G02-PSX 1996-09-11 02:38 1996-09-11 03:18
C3 C03-CALL 1996-11-04 13:15 1996-11-04 14:00
E4 E04-EUR 1996-12-19 06:35 1996-12-19 07:22
G8 G08-QRS 1997-05-06 13:00 1997-05-06 15:09
C9 C09-CALL 1997-06-25 13:25 1997-06-25 14:11
C9 C09-DAWN 1997-08-23 14:07 1997-08-23 16:09
C9 C09-TAR 1997-06-28 13:50 1997-06-28 14:51
C9 C09-DSK1 1997-07-04 14:09 1997-07-04 16:07
C9 C09-DSK2 1997-07-14 10:03 1997-07-14 10:48
C9 C09-DSK3 1997-07-23 13:11 1997-07-23 13:57
C9 C09-APJ 1997-08-07 11:06 1997-08-07 12:47
C10 C10-CALL 1997-09-16 23:49 1997-09-17 00:49
C10 C10-EQX 1997-09-18 22:35 1997-09-18 23:21
E11 E11-EUR 1997-11-06 20:09 1997-11-06 22:51
E12 E12-EUR 1997-12-16 11:43 1997-12-16 12:28
E14 E14-EUR 1998-03-29 13:05 1998-03-29 14:00
E15 E15-EUR 1998-05-31 20:42 1998-05-31 21:43
E15 E15-EUR 1998-05-31 20:42 1998-05-31 21:43
E18 E18-PSX 1998-12-10 19:36 1998-12-11 00:23
E19 E19-EUR 1999-02-01 01:49 1999-02-01 02:38
C20 C20-PJOV 1999-05-03 16:00 1999-05-03 18:00
C21 C21-PJOV 1999-07-01 23:52 1999-07-02 01:47
C22 C22-PJOV 1999-08-12 08:18 1999-08-12 13:06
C23 C23-PJOV 1999-09-14 14:36 1999-09-14 21:28
I24 I24-IO 1999-10-11 03:42 1999-10-11 06:41
I25 I25-TOR 1999-11-25 21:06 1999-11-26 05:54
E26 E26-EUR 2000-01-03 17:29 2000-01-03 18:30
I27 I27-TOR 2000-02-22 10:22 2000-02-22 12:15
I27 I27-IO 2000-02-22 13:05 2000-02-22 14:25
I31 I31-IO 2001-08-06 04:31 2001-08-06 05:28
I32 I32-RAMP 2001-10-15 15:31 2001-10-15 17:26
I32 I32-TOR 2001-10-15 21:53 2001-10-15 23:23
A34 A34-PSX7 2002-11-05 01:05 2002-11-05 05:45
Zero Levels
-----------
In general, the zero levels of the spin plane sensors have been
corrected to approximately 1/4 of the digitization step size
(i.e. if the step size is 8 nT, the zero level is good to 2 nT)
or 0.01 nT, which ever is larger. Spin plane sensor zero levels
are continuously adjusted by removing spin period averages in
the spinning reference frame. The spin aligned sensor zero levels
are monitored and adjusted at least once per orbit. The spin
aligned sensor zero levels are assumed to drift slowly and
linearly. The exception to this statement occurs at times
identified as 'offset anomalies' (see Table 7) where all three
sensors in a triad show large (2-3 nT) jumps in the zero levels.
These anomalies have been corrected in the processed data. In
general, the spin aligned sensor zero level is reliable to 0.1 nT.
Errors in zero level corrections appear as harmonics of the
spacecraft spin period as modified by the averaging window. The
nominal spacecraft spin period is 19 seconds and the most common
sample rates are 24 and 12 seconds.
Outboard Sensor Zero Levels
---------------------------
Zero levels in the outboard sensor have proven to be strongly
temperature dependent. Offsets changed linearly with temperature
during the Earth-Jupiter Cruise mission phase where temperatures
went from 280-220 K. At Jupiter, where temperatures have been
lower than the instrument qualification ranges, offsets at
Jupiter have experienced occasional episodes of instability.
Offset changes may occur instantaneously or rapidly (over a
period of minutes). In some cases the offset has drifted back to
previous values over a period of days or months. In other cases
the offset has returned to it's original value sharply. In all
cases an attempt has been made to correct for these offset
in the processing so that the data appear continuous. Table 7
contains a listing of major offset anomalies.
Gains
-----
The sensor gains were determined in ground calibration and
verified in-flight. In-flight verification included comparison
of Earth flyby data with model fields and monitoring for
sensor gain changes using the MAG internal calibration coils.
In general, the gains have remained stable throughout the
mission. There has been a slight change (linear) in the
absolute gain levels associated with the sensor temperature.
Gains are believed to be known to substantially better than one
percent.
Geometry
--------
Geometry corrections for sensor mounting and non-orthogonality
are applied through the sensor coupling matrix. Although the
sensor triads are rigid and are not believed to have changed
geometry through time, the triad itself is flipped periodically
to rotate the spin aligned sensor into the spin plane. Small
variations (<0.1 degree) in the triad mounting with respect to
the spacecraft coordinate system must be corrected after each
sensor flip. This is done by computing a new coupling matrix.
The data are despun by using the 'rotor spin angle' that is
broadcast on the spacecraft bus by the spacecraft attitude and
articulation control system (AACS). Despinning must be corrected
in ground processing to account for delays in the MAG instrument
electronics and filters. This task is accomplished by respinning
the data using the raw AACS data and then despinning using a
corrected spin angle. The total correction can be as large as
two degrees. After ground processing, the MAG data are
geometrically correct to better than one degree, and probably
better than 0.1 degree.
Optimal Averager AACS
---------------------
Two of the rotor attitude angles supplied in the IRC data files,
Rotor Twist and Rotor Spin, are always flagged when the opt/avg
was being used to capture the data. The opt/avg produces
extremely low sampling rates (typically >32 min/sample).In
addition in the engineering stream the various rotor attitude
angles are sampled asynchronously both from each other and from
the MAG data. As a result any rotor attitude information provided
at the MAG sampling times must be interpolated. While the other
two angles vary only slowly, the twist and spin angles vary over
0-2 pi at the spacecraft spin period (~20 sec). Since the MAG
data produced by the opt/avg represent averages over many spin
periods it is not meaningful to assign specific twist or spin
angles to the data. It is also not possible to 're-spin' the
data, which is the purpose of providing Rotor Twist and Spin in
the first place.
Slew Tests
----------
Due to the continuing gyro electronics problems that were first
observed in E12, a series of 'slew tests' were implemented in
order to access gyro functioning. During these tests, because of
the potential for anomalous behavior by the gyros, the spacecraft
attitude is not known with any certainty. This poses problems for
both the B-field components and AACS. Opt/avg data, because of the
relatively short duration of the tests and the long averages of
the data, show no real effects from the corruption. The RTS data,
however, can show the effects very clearly. As a result the
B-field components have been flagged when a slew test was
performed with the instrument in RTS mode, and the components were
preserved when the instrument is in opt/avg mode. The components
were flagged in the RTS data even when no corruption was readily
apparent. The flagged data are available in the Galileo Jupiter
MAG raw data set.
The following table gives the timing of the slew tests. The times
indicated correspond to the start and end of the group of commands
that constituted a slew test. The interval in which the B-field
components actually become corrupted was shorter than this. This
corrupted interval started approximately with the 'SLEW TEST'
and ended with the 'ENABLE SEQID,RESD HVEC' (see MAG EVENT TABLE).
Mode indicates whether the instrument was in RTS or OPT/AVG mode.
A value of 'N/A' indicates that the slew test occurs in a data
gap.
-----------------------------------------------------
Table 6. Slew tests
-----------------------------------------------------
Orbit Start Time Stop Time Mode
-----------------------------------------------------
E14 1998-05-13 12:40 1998-05-13 14:23 OPT/AVG
E17 1998-11-07 17:00 1998-11-07 20:38 OPT/AVG
E19 1999-04-27 21:32 1999-04-27 21:40 OPT/AVG
I24 1999-10-13 16:42 1999-10-13 18:23 OPT/AVG
I24 1999-10-27 12:00 1999-10-27 14:15 RTS
I25 1999-11-28 07:27 1999-11-28 09:08 N/A
I25 1999-12-09 01:00 1999-12-09 03:15 OPT/AVG
E26 2000-01-05 19:12 2000-01-05 20:53 OPT/AVG
E26 2000-02-07 15:00 2000-02-07 17:15 OPT/AVG
I27 2000-02-23 17:52 2000-02-23 19:33 N/A
I27 2000-03-27 16:00 2000-03-27 18:15 OPT/AVG
G28 2000-05-22 00:12 2000-05-22 01:53 RTS
G28 2000-06-23 19:30 2000-06-23 21:45 OPT/AVG
G28 2000-08-31 07:42 2000-08-31 09:23 OPT/AVG
G28 2000-10-18 22:12 2000-10-18 23:53 OPT/AVG
G28 2000-12-07 21:42 2000-12-07 23:23 RTS
G29 2000-12-30 01:32 2000-12-30 03:13 RTS
G29 2001-03-07 17:00 2001-03-07 19:15 OPT/AVG
G29 2001-05-14 16:00 2001-05-14 18:15 OPT/AVG
C30 2001-05-26 01:00 2001-05-26 02:41 N/A
C30 2001-07-05 23:00 2001-07-06 01:15 OPT/AVG
I31 2001-08-07 20:00 2001-08-07 21:41 N/A
I31 2001-08-23 23:00 2001-08-24 01:15 OPT/AVG
I32 2001-10-17 03:40 2001-10-17 05:21 RTS
I32 2001-11-19 16:00 2001-11-19 18:15 OPT/AVG
I33 2002-01-18 18:00 2002-01-18 19:41 RTS
I33 2002-04-03 16:00 2002-04-03 18:15 OPT/AVG
I33 2002-06-05 16:00 2002-06-05 19:15 OPT/AVG
I33 2002-10-07 17:20 2002-10-07 20:35 OPT/AVG
I33 2002-10-24 17:30 2002-10-24 20:45 RTS
A34 2002-11-13 23:30 2002-11-14 02:11 N/A
A34 2003-01-07 22:00 2003-01-08 01:15 OPT/AVG
Anomalies
---------
Sector Data Loss Due to Thruster Flushes:
Thruster flushes (RPM PROPEL LINES VENT) cause the loss of sector
(rotor twist) data onboard the spacecraft. This loss results in
the corruption of RTS and opt/avg data which depend upon sector
data for their onboard despinning. As a result RTS and opt/avg
data taken during thruster flushes should not be trusted.
Where they have been identified intervals of data affected by
this problem have been removed from this data set.
Offset Anomalies:
Table 7 lists the offset anomalies that occurred over the course
of the mission. These anomalies typically consisted in an
instantaneous jump in the zero-level over all three sensors,
though in some cases there was a slower drift. The anomaly times
represent the times at which this jump was evident in the data.
In some instances, these events occcurred when the affected
magnetometer was not in use. In these cases the offsets had one
set of values when turned off, and a different set when turned on
some time later. The time given for these cases is the time at
which the magnetometer was turned back and the anomaly is
indicated as having happend 'before' that time.
While zero-levels for the inboard magnetometer did change over
time, as evidenced by the below table the outboard magnetometer
proved much more unstable than the inboard (URLR was the mode
most commonly used in the outboard magnetometer). Because of its
instability, the outboard instrument it was not used between C10
and G29. Had it been used additional anomalies may well have been
observed in this time period.
----------------------------------
Table 7. Offset Anomalies
----------------------------------
Orbit Mode Time
----------------------------------
E4 URLR before 96-12-29 21:10
E6 URLR before 97-03-03 19:10
G7 URLR before 97-04-12 07:00
G7 URLR 97-04-16 15:19
C9 IRLR 97-06-22 16:05
C9 URLR before 97-07-02 10:00
C10 URLR before 97-09-25 19:38
C10 URLR 97-10-05 14:53
G29 URLR 01-02-07 06:11
C30 URLR before 01-05-29 14:00
I31 URLR before 01-08-12 02:30
I31 URLR 01-09-12 08:00
I32 URLR before 01-10-21 15:30
Jupiter Orbital Insertion (JOI):
Prior to the JOI burn the spacecraft spin rate was increased in
order to make it more stable for the firing of the main engine.
In addition there was no high-resolution AACS through this
interval. As a result of the variable spin rate and lack of
high-resolution AACS it was not possible despin the MAG data. As
a result only the magnetic-field magnitude is provided.
Callisto 3 Orbit:
The data from the inboard sensor, low field, flip right mode
acquired during the third orbit was irrecoverably corrupted.
Data from this orbit should be used with caution, particularly
in applications where the field orientation needs to be known
to better than a few degrees. At the beginning of the orbit,
the inboard sensor was commanded to flip right. We believe that
when this flip occurred, the sensor triad failed to lock into
place properly. As a result, the sensor triad appears to
'jiggle' resulting in an unstable geometry. The extent of this
jiggle is unknown but is believed to be on the order of a degree
or so. One of the impacts of the unstable sensor geometry is that
the sensor offsets, which are a combination of spacecraft fields
and sensor zero levels, vary on short time scales. In order to
reduce the spin harmonics attributable to offsets in this orbit,
the RTS data have been averaged using a 120 second window on
24 second centers.
Callisto 9 and 10 Orbit Opt/Avg:
In orbits C9 and C10 the magnetometer was commanded into opt/avg
mode without deselecting the instrument from RTS. As a result the
Command and Data Subsystem (CDS) overwrote the opt/avg rate
filter constant stored in MAG memory with a RTS rate filter
constant. This resulted in the data being under filtered relative
to the data sample rate. This under filtering shows up as
spin-tone in the spinning sensors in spacecraft coordinates. In
order to eliminate the spin-tone the raw data has been averaged
(two point averages on one point centers). Averaging has been
performed on the following intervals:
----------------------------------------
Table 8. Averaged intervals for
underfiltered opt/avg data
----------------------------------------
Orb Start Time Stop Time
----------------------------------------
C9 1997-07-10T18:15 1997-07-11T10:58
C9 1997-08-01T14:50 1997-08-02T17:07
C9 1997-09-11T17:04 1997-09-11T21:01
C10 1997-09-29T11:36 1997-09-30T11:52
Europa 17 MAG and AACS instability:
Between 1998-09-26T15:46:24 and 1998-09-26T16:42:01 the AACS data
are unstable. Apparently, some form of AACS calibration was
occurring. During this period, the magnetometer spin plane
components appear to slowly rotate and then jump back to a
correct orientation. This problem occurred on the spacecraft and
has not been corrected in the ground system processing.
Europa 19 AACS Data Gap:
Due to a spacecraft anomaly AACS data from 1999-01-31 16:02:06 -
1999-02-01 01:49:37 (which were being stored in the Multi User
Buffer) were never returned. The MAG data from this interval,
however, were written to tape and returned later. Recovering the
lost AACS - specifically the rotor right-ascension (RA), and
declination (DEC) - was complicated by two Science Instrument
Turns (SITURN's) which occurred in the missing interval. In
between the SITURN's, RA and DEC were interpolated by the
following means:
1/31 16:02:06 to 18:01:28 - set to last known value
1/31 18:01:28 to 18:26 - linearly interpolated
1/31 18:26 to 19:31:27 - assumed constant between
SITURN's and determined by examination
1/31 19:31:27 to 19:49 - linearly interpolated
1/31 19:49 to 2/1 01:49:37 - set to next known value (taken
from high-res. data, the E19-EUR recording)
AACS instability Callisto 21 - Callisto 23:
The AACS data for the Callisto 21, Callisto 22, and Callisto 23
perijove recordings (C21-PJOV, C22-PJOV, and C23-PJOV) were
seriously corrupted. While similar problems are not evident in
the RTS and opt/avg data, care should be taken in the use of
these lower rate data as well. For Orbit 23 it was necessary to
interpolate the rotor twist and spin angles of the intervals:
1999-09-17 05:26:41 to 06:08:30 and 1999-09-27 16:06:58 to
16:28:53.
Io 25 Data Gaps Due to Corruption by Snapshots:
Following recovery from spacecraft safing, MAG was inadvertently
left in snapshot mode. As a result there are numerous short gaps
where the RTS data were corrupted by snapshots, and a large gap
where the OPT/AVG data were overwritten. This problem affects
the interval 1999-11-26 04:32 to 1999-11-29 00:54.
Europa 26 Data Rate Anomaly:
The packet headers for the data from the time interval
2000-01-01 23:30:00.000 to 2000-01-03 14:08:39.742 indicated that
the data were sampled at 18 minor frames (mf) or 12 seconds
sampling resolution. This data rate matched the MAG RTS format
reported in the sequence (format E). In the original 12 second
data there were a series of systematic gaps. The end of each gap
occurred where the packet of MAG data included a time tag. This
would be the case if an incorrect sampling rate were applied to
the data in packets where no time tag is given, then the data
were to jump forward to the correct time when a time tag was
given. Accordingly the data in this interval were re-time tagged
at 36 mf (24 second) samples. This done the data became
continuous across what were previously gaps -- both in time (the
data are evenly sampled), and data value (the data contain no
steps). The reason for this discrepancy was unknown.
Io 33 Offset Instability:
The spin-plane offsets in the outboard sensor (URLR mode) were
highly unstable for the RTS data. This includes the following
intervals:
2002-01-22 20:30 - 2002-01-31 13:00
2002-10-22 00:00 - 2002-10-31 12:30
While an attempt was made to correct the offsets, some problems
may still exist (see 'Zero Levels'). Additionally, the zero level
instability may indicate that the sensor was about to fail. For
both of these reasons, the data from these two intervals should
be treated with some suspicion.
Io 33 opt/avg data timing:
The timing of the opt/avg data in the interval 2002-Sep-28 13:00
to 2002-Oct-02 23:15 are somewhat questionable and the data should
be treated with some caution. According to the planned sequence,
the data collected after the opt/avg on command given at
2002-09-28 12:05, were due to be read out with the MRO scheduled
for 2002-10-02 18:00. However, due to the spacecraft safing that
occurred 2002-10-02 03:38 the MRO was not executed. Since the
spacecraft was still safed, the subsequent opt/avg on command
(2002-10-02 19:05) was also not executed and the data were not
overwritten. Thus when the MRO commanded at 2002-10-07 10:00 was
executed the data returned appear to have been from the opt/avg at
2002-09-28 12:05 -- and not from the opt/avg at 2002-10-02 19:05
as originally planned. The data in this interval have been timed
according to this assumed sequence of events.
Amalthea 34 data coverage:
Spacecraft operations ended on 2003-01-15. As a result there is a
large gap in coverage from about that time until 2003-09-21 when
operations resumed briefly to record the spacecraft's plunge into
the Jovian atmosphere. Between these two times an occasional
single (8 hour) pass of data was provided as a monitor of
instrument health. However, these monitoring data are not included
as part of this data set. The reasons for omitting these data are
that their sporatic nature limits their usefulness, and a lack of
AACS data prevents them from being fully processed. These
monitoring data are included in the Galileo at Jupiter MAG raw
data set.
Jupter 35 AACS:
The AACS returned in J35 had Earth Receive Times (ERTs) on
2003-09-21, but Spacecraft Event Times (SCETs) on 2003-01-22. In
processing the J35 data it was assumed that the ERTs were correct
and that the SCETs were incorrect, meaning that the values of RA
and DEC were approximately correct. Due to the difficulty of
precisely determining the correct timing of the AACS data, the
RA, DEC, and rotor spin delta were set to the most common values
for the interval, and the rotor spin angle, and rotor twist angle
were calculated from them.
Product Versions
================
The following table describes the various versions of the data
files.
--------------------------------------------------------------------
Table 9. Data product versions
--------------------------------------------------------------------
Product
Version
ID Description
--------------------------------------------------------------------
1 original release
2 opt/avg data timing was corrected: a previous error in
the time tagging of the opt/avg data resulted in that
data being shifted earlier in time by one averager step.
3 JSO coordinates were added (and included with JSM
coordinates); a 'CORRECTED TIME' column, which has a
filter response time applied to the 'SAMPLE TIME' was
added to the SYS3, JSE, and JSO/JSM coordinate data
files; SYS3 coordinate file was modified to include both
east and west longitude columns; a variety of changes
were made to record formats
Limitations
===========
There are no particular limitations or warnings regarding the
use of these data, in general, that are not described above.
Users should review the PDS label files associated with
individual data files for file (orbit) specific warnings."
END_OBJECT = DATA_SET_INFORMATION
OBJECT = DATA_SET_TARGET
TARGET_NAME = JUPITER
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = IO
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = EUROPA
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = GANYMEDE
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = CALLISTO
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = AMALTHEA
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = "IO PLASMA TORUS"
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_HOST
INSTRUMENT_HOST_ID = GO
INSTRUMENT_ID = MAG
END_OBJECT = DATA_SET_HOST
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = DESSLER1983
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = ERICKSONETAL1999
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = ERICKSONETAL2000
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = HUDDLESTONETAL1998A
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = KIVELSONETAL1992
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = KIVELSONETAL1996A
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = KIVELSONETAL1996B
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = KIVELSONETAL1997A
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = MITCHELLETAL1998
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
END_OBJECT = DATA_SET
END