Cassini MIMI LEMMS Raw Data Description
MIMI - Magnetospheric Imaging Instrument
LEMMS - Low Energy Magnetospheric Measurement System
PDS3 DATA_SET_ID = CO-E/J/S/SW-MIMI-2-LEMMS-UNCALIB-V1.1
ORIGINAL DATA_SET_NAME = CASSINI E/J/S/SW MIMI LEMMS SENSOR UNCALIBRATED DATA V1.1
START_TIME = 1999-01-03T00:00:00
STOP_TIME = 2017-09-15T23:59:59
PDS3 DATA_SET_RELEASE_DATE = 2018-07-01
PRODUCER_FULL_NAME = Jerry W. Manweiler
Data Description
================
Data Overview
=============
The Cassini Magnetospheric Imaging Instrument (MIMI) Low Energy
Magnetospheric Measurement System (LEMMS) raw data bundle
includes all data collected from the MIMI Data Processing Unit during
the entire Cassini mission. The original data has been decommutated
and decoded by software at the Applied Physics Laboratory (APL) and has
been then further ordered and filtered by software at Fundamental
Technologies, LLC. The data are provided in raw, uncalibrated form in conjunction
with a PDS MIMI calibration documents (urn:nasa:pds:cassini-mimi-lemms-raw:document)
which provides specific algorithms for the derivation of calibrated data. This
bundle includes raw, uncalibrated values for each energy channel for
the LEMMS sensor for all times during the mission including the Earth flyby,
the Jupiter flyby, interplanetary cruise, and the entire Saturn tour.
Data are presented in a set of tables which are of variable length and use a
comma to separate various fields. These data are intended to be the most
comprehensive and complete data included in the Cassini MIMI LEMMS archive.
Browse data are included with Key Parameter data that is calibrated using
the algorithms provided in the Calibration document. In addition, a series of
images are provided with the KP browse data that displays the KP data which
can lead the user to the particular times of interest. These data should be
among the first used by a user of any of the MIMI LEMMS archive as it
will lead one to information required to search for more detailed or
highly specialized features in the original data.
Parameters
==========
These data comprise low energy charge particle count rate
measurements for each energy channel of the LEMMS detector in a
regular and high time rate mode. In addition these data include
LEMMS PULSE HEIGHT ANALYSIS measurement data for a statistically
select sample of the particle measurements. The data collections are:
LEMMS Accumulation Rate Data - low energy charge particle count rate
measurements
LEMMS Fine Rate Accumulation Data - low energy charge particle count
rate measurements for a select
list of channels at a high time
resolution.
LEMMS Pulse Height Analysis Data - Statistically sampled set of
discrete particle measurements.
The data are organized in time by the spin of the spacecraft. When the
spacecraft is in staring mode then the MIMI DPU automatically creates
a virtual spin that divides the time collection periods into 16
sectors, 16 subsectors, and 16 microsectors and maintains a simple
organizational structure for characterizing the collection of the time
into time segments. When the spacecraft is spinning at a minimally
defined spin rate (adopted by the MIMI DPU) then the MIMI data is
automatically segregated into 16 sectors, 16 subsectors, and 16
microsectors. When the spacecraft is spinning and the LEMMS
instrument is rotating the LEMMS rotation period is synchronized to
the spacecraft spin period so that there are 16 sectors in a spin, 16
subsectors in a sector and 16 microsectors in a subsector.
Processing
==========
Data in this bundle were processed by the use of a number of
software programs which assemble segmented mini-packets in the raw
telemetry packets into complete sets, de-compress the data that were
compressed by one of a number of compression algorithms by the MIMI
flight software onboard and organize the channel data into
appropriate time segments.
Data
====
The MIMI LEMMS raw collections include three ASCII CSV tables
(each associated with a data collection) of count rate data as a
function of time collected from the MIMI LEMMS Detectors and collated
into channel sets. Each table contains variable length records for
which the fields are comma delimited.
LEMMS Accumulation Rate Data
----------------------------
Fields include:
a purpose identifier where science data records are identified
with purpose = sci
starting and ending ephemeris times
Spin, sector, subsector (and for LEMMS Fine Rate (FRT) data
microsector)
SCLOCK and spin period that are used to derive the starting
ephemeris time
Notes regarding the SCLOCK value:
1. Only the SCLOCK major segment value is provided - MIMI
currently does not have access to the fine SCLOCK value
hence SCLOCK resolution is limited to +- 1/2 SCLOCK count
2. The SCLOCK is only available from telemetry at the
beginning of each spin. All other published SCLOCKS are
derived from the spin starting SCLOCK, the spin numbers
(for the current and next available spins), and the spin
period.
3. SCLOCK values are assumed to drive the value of the
ephemeris times and not vice-versa. All effort is made to
validate the published ephemeris times but since updates to
the Cassini SCLOCK kernel in SPICE can occur the values of
ephemeris time are only as accurate as the currently
published Cassini SCLOCK SPICE kernel.
Spacecraft staring mode where staring = 0 when spinning and 1
otherwise
LEMMS Channel count rate data organized as:
Low Energy Telescope channels
A0-A8 - These channels are sensitive to protons and heavier
ions. The A0-A4 channels are somewhat sensitive to
electrons.
B0-B3 - These channels are sensitive to protons and He.
BE - This channel is sensitive to 1 - 2.6 MeV energetic
electrons.
C0-c7 - These channels are associated with magnetically
sweeped particles and are sensitive to electrons
AS, BS, ES, FS are the singles rates measured by the A, B, E
and F detectors.
E2/F2S is the ratio of the E2 to F2 singles rates
High Energy Telescope channels
E0-E7 - These channels are sensitive to electrons and somewhat
sensitive to X-rays
G1 - This channel is sensitive to X-rays only
P1-P9 - These channels are mainly sensitive to protons.
P1-P2 are sensitive to all species of charged
particles and X-rays
P7-P9 are also sensitive to He
H1-H5 - These channels are sensitive to He and heavier species
H5 is also sensitive to 20-25 MeV protons
Z1-Z3 - These channels are sensitive to species heavier than
He
D1-D3, D41 are the singles rates for each of the D detectors
in the LEMMS system
Priority Channels
In various portions of the mission, a subset of main channels
are identified to provide high time resolution data (for each
two microsectors). The totals of the sums for each of these
priority channels are included in the list of channels for
diagnostic use. The number and specific selection of priority
channels varies over the life of the mission.
LEMMS Center look angle in Degrees, which provides the angle
between the pointing of the low energy telescope of the LEMMS
instrument with respect to the -Z axis.
The LEMMS instrument rotates around the -Y axis.
LEMMS Fine Rate Accumulation Data
---------------------------------
Fields include:
a purpose identifier where science data records are identified
with purpose = sci
starting and ending ephemeris times
Spin, sector, subsector (and for LEMMS Fine Rate (FRT) data
microsector)
SCLOCK and spin period that are used to derive the starting
ephemeris time
Notes regarding the SCLOCK value:
1. Only the SCLOCK major segment value is provided - MIMI
currently does not have access to the fine SCLOCK value
hence SCLOCK resolution is limited to +- 1/2 SCLOCK count
2. The SCLOCK is only available from telemetry at the
beginning of each spin. All other published SCLOCKS are
derived from the spin starting SCLOCK, the spin numbers
(for the current and next available spins), and the spin
period.
3. SCLOCK values are assumed to drive the value of the
ephemeris times and not vice-versa. All effort is made to
validate the published ephemeris times but since updates to
the Cassini SCLOCK kernel in SPICE can occur the values of
ephemeris time are only as accurate as the currently
published Cassini SCLOCK SPICE kernel.
Spacecraft staring mode where staring = 0 when spinning and 1
otherwise
LEMMS Channel count rate data organized based upon the current set
of priority channels The set of priority channels changes from
time to time during the mission. The specific channels for any
particular data file are identified by the headers of that data
file.
LEMMS Center look angle in Degrees, which provides the angle
between the pointing of the low energy telescope of the LEMMS
instrument with respect to the -Z axis. The LEMMS instrument
rotates around the -Y axis.
LEMMS Pulse Height Analysis Data
--------------------------------
Fields include:
a purpose identifier where science data records are identified
with purpose = sci
starting and ending ephemeris times
Spin, sector, subsector
SCLOCK and spin period that are used to derive the starting
ephemeris time
Notes regarding the SCLOCK value:
1. Only the SCLOCK major segment value is provided - MIMI
currently does not have access to the fine SCLOCK value
hence SCLOCK resolution is limited to +- 1/2 SCLOCK count
2. The SCLOCK is only available from telemetry at the
beginning of each spin. All other published SCLOCKS are
derived from the spin starting SCLOCK, the spin numbers
(for the current and next available spins), and the spin
period.
3. SCLOCK values are assumed to drive the value of the
ephemeris times and not vice-versa. All effort is made to
validate the published ephemeris times but since updates to
the Cassini SCLOCK kernel in SPICE can occur the values of
ephemeris time are only as accurate as the currently
published Cassini SCLOCK SPICE kernel.
Spacecraft staring mode where staring = 0 when spinning and 1
otherwise
LEMMS Detector Channel count rate data is an array of counts for
each of the three low energy telescope solid state detectors. Each
field contains the counts observed within each of the 64 energy bins
for each of the detectors (A, E1, and F1) accumulated over the
specific time interval. The Detector energy bins are
quasi-logarithmically spaced. See the MIMI_CALIBRATION calibration
file for spacing deltas and min and max energies.
LEMMS Center look angle in Degrees, which provides the angle between
the pointing of the low energy telescope of the LEMMS instrument
with respect to the -Z axis. The LEMMS instrument rotates around
the -Y axis.
Ancillary Data
==============
Included in the Cassini MIMI bundle are ancillary data files
(urn:nasa:pds:cassini-mimi:data-ancillary) representing the
MIMI Key Parameter (KP) data. The MIMI KP data is a calibrated subset
of the important channels for each of the MIMI detectors. The subset
of channels have been identified to most reasonably show characteristic
energetic particle events during the mission. The KP data is calculated
at an arbitrarily defined 60 second cadence which is different than the
approximate collection times for the instruments as identified below for
standard operations: (It must be realized that the collection times vary
based upon the telemetry rate but nothing more than a factor of 2, 4, or 8.)
Instrument Product Type Approx Collection Time (s)
------------------------------------------------------------
LEMMS Accumulation 5 (each subsector)
LEMMS Fine Rate 0.6 (each microsector)
LEMMS PHA 5 (each subsector)
Data points for each record of the KP data are first Median Quartile
Filtered then averaged (except in the case where the median is zero)
for each sector. The sectored data is then interpolated into the 60
second data cadence of the KP data file. The KP data is then
converted into a flux in units of 1/(cm^2*sr*sec*KeV)
Browse
======
Browse plots for each of the KP data files are produced. There are 7
different browse plots available.
Inst Wild Card File Name Plotted KP data
---------------------------------------------------------------------
LEMMS LEMMS_KP_ELEC_(yyyydoy)_(ver#).JPG KP LEMMS Electron flux
LEMMS LEMMS_KP_ION_(yyyydoy)_(ver#).JPG KP LEMMS Ion flux
Usage Note
----------
The KP browse data and associated browse plots are to be used as an
initial characterization of the particle environment and are NOT to
be used for publications. The data is not at publication quality
and is provided as is.
Coordinate System
=================
The data in this bundle are measurements of count rates based upon
the orientation of the LEMMS instrument (LEMMS Center look direction).
Particle flux effects are then determined by transforming from a
spacecraft centered coordinate system, properly rotated to account for
the appropriate LEMMS telescope and look direction, into whatever
external coordinate (reference system) is most appropriate.
Software
========
There is no sample software provided as of the writing of this catalog
file although the calibration volume does provide algorithms for
conversion of count rates into flux.
Media/Format
============
These data are supplied to the Planetary Data System via electronic
means and are then broken into segments based upon the media currently
prescribed by PDS.
Confidence Level Overview
=========================
These data contain all calibrated data for the LEMMS Detector as
part of the Cassini MIMI instrument for the interval described above.
Every effort has been made to ensure that all data returned to APL
from the spacecraft is included and that the calibrated browse data
products are accurate.
The LEMMS C0 channel (and less so for the C1 channel) has occasional
exceptionally high rates (spectral indexes exceeding 6) that are due
either to direct solar exposure and/or to specular reflection from
various parts of the spacecraft. This was first identified during the
Earth - Jupiter Cruise phase of the mission. Priority channels were
reorganized during this time but with the unexpected result that the
C1 channel was being corrupted without the ability to identify the
source of the corruption at a high time resolution which the priority
channels provide. Just prior to SOI the priority channels were again
re-established to include the C0 channel for the specific purpose of
enabling the data user to develop algorithms to eliminate those data
values that include this contamination.
The low energy A (A0 - A4) channels are subject to contamination by
electrons.
As of January 2005, the LEMMS detector no longer has the ability to
rotate. Various attempts to correct this anomaly have been tried with
the result of moving the fixed position to other nearby pointing
directions but these attempts have failed in their ability to restart
full motion of the detector.
Review
======
The MIMI LEMMS data was reviewed internally by the Cassini MIMI
team prior to release to the PDS. The bundle has also been peer
reviewed by the PDS-PPI Node.
Data Coverage and Quality
=========================
All data in the stated interval are included, to the best of our
knowledge and attempts to determine completeness. In general, the
instrument was operated only briefly during early tour for the
following intervals:
1. Antenna deployment 1997-10-25T00:00 - 1997-10-26T05:30
2. Venus 1 flyby 1998-04-26T12:54 - 1998-05-08T19:21
3. Instrument Checkout 1998-12-30T09:10 - 1999-01-19T05:40
4. Venus 2 flyby 1999-06-24T09:08 - 1999-06-24T21:20
5. Earth flyby 1999-08-13T17:39 - 1999-09-14T22:20
Only data for interval 5 is provided to PDS due to technical issues in
processing.
Beginning in February of 2000 the instrument was operated more-or-less
continuously with small daily runs of approximately 8 hours.
Intermittent data collection occurred during 2002 and 2003 with
multiple day gaps in the data
Large Data Gaps:
1. Cruise 2000-066 - 2000-155
2. Cruise 2000-210 - 2000-246
3. Cruise 2000-311 - 2000-320
4. Cruise 2000-322 - 2000-333
5. Post Jupiter Cruise 2003-018 - 2003-104
6. Post SOI 2004-187 - 2004-193 - Spacecraft safing
shut off
7. Saturn 2012-293 - 2012-303 - propellant gauging test
Those days for which the instrument did not collect data either due to
the instrument being off or due to communication issues, the collections
will not contain any files.
Limitations
===========
As noted above the A0 and C0 channels (and somewhat less so the C1, A1
and additional C and A channels) have occasional significant
corruption of the count rate due to direct solar pointing and/or due
to specular reflection of UV from various parts of the spacecraft.
There has as yet been no systematic algorithm developed to capture
when these events occur either by the spectral power of the data or
else by the pointing excepting in the situation when the LEMMS
instrument itself is directly pointed into the Sun. This last
situation can be easily identified by using the SPICE routines.
The KP browse data and associated browse plots are to be used as an
initial characterization of the particle environment and are NOT to be
used for publications. The data is not at publication quality and is
provided as is.
References:
===========
Krimigis, S.M., D.G. Mitchell, D.C. Hamilton, S. Livi, J. Dandouras,
S. Jaskulek, T.P. Armstrong, J.D. Boldt, A.F. Cheng, G. Gloeckler,
J.R. Hayes, K.C. Hsieh, W.-H. Ip, E.P. Keath, E. Kirsch, N. Krupp,
L.J. Lanzerotti, R. Lundgren, B.H. Mauk, R.W. McEntire, E.C. Roelof,
C.E. Schlemm, B.E. Tossman, B. Wilken, and D.J. Williams, Magnetosphere
Imaging Instrument (MIMI) on the Cassini Mission to Saturn/Titan,
Space Sci Rev. 114, 233-329, 2004.
(https://doi.org/10.1007/s11214-004-1410-8)
Kusterer, M.B., L.M. Burke, Level 1A File Layouts, Cassini/MIMI
Data Analysis Center Level 1A File Layouts, The Johns Hopkins
University Applied Physics Laboratory Document, Revision 18,
December 2003.
Manweiler, J.W., W.A. Rasmuss, and S. Joy, MIMI Standard Data
Products and Archive Volume Software Interface Specification,
v2.1, JPL Document D-31634, Cassini document IO-AR-006, 2005.
J.D. Vandegriff, R. DiFabio, D. Hamilton, M.B. Kusterer,
J. Manweiler, D.G. Mitchell, C. Paranicas, E. Roussos,
Cassini/MIMI Instrument Data User Guide
|