DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains Raw data taken by New Horizons
Solar Wind Around Pluto
instrument during the JUPITER mission phase.
SWAP comprises electro-optics and detectors to obtain count rate measurements
of the solar wind; measuring the solar wind before, during and after the Pluto
encounter will allow characterization of the atmospheric escape rate of Pluto.
The SWAP electro-optic elements select the angles and energies of the solar
wind and pickup ions to be measured; ions thus selected are registered with a
coincidence detector system. SWAP measures the energy spectrum of ions in its
environment by varying (also called scanning or sweeping) voltages of the
electro-optics over many steps during a short time period. SWAP can also
immediately follow a sweep of coarse voltage steps with a sweep of finer
steps, centered on the peak measurement of the coarse sweep, to obtain a
higher resolution of that portion of the energy spectrum.
There are three types of SWAP science data: real-time; summary; histogram.
Real-time data, at rates up to 1Hz, provide the most detailed science
measurements since they contain the full count rate distribution as a function
of energy (speed). For science summary and science histogram modes, the full
distribution is not recorded. Instead, parameters are derived from the count
rate distribution stored by SWAP. These derived parameters require less memory
than storing the whole distribution. The science summary and science histogram
modes are primarily used during the cruise phase of the mission. For science
data, the common data product is usually a binary table; for calibrated
real-time data, spectrograms as images are also provided. Typically the tables
have instrument parameters and measurements in the columns and measurement
times in the rows, but the actual format depends on the type of data and the
processing level (raw vs. calibrated). Other tables containing houskeeping and
other parameters are also provided. This data set includes documentation for
all data types and formats.
During the Jupiter mission phase, SWAP made near-continuous
science observations, taking data between 2 and 12 times per hour.
Inbound to Jupiter, real-time science mode data were taken twice
per hour, then 12 measurements were recorded per hour in the
Jupiter tail. The Jupiter tail observations continue until about
100 days after closest approach, which corresponds to about 2200
RJ downstream.
Every observation provided in this data set was taken as a part of a
particular sequence. A list of these sequences has been provided in
file DOCUMENT/SEQ_SWAP_JUPITER.TAB.
N.B. Some sequences provided may have no corresponding observations.
For a list of observations, refer to the data set index table. This
is typically INDEX.TAB initially in the INDEX/ area of the data set.
There is also a file SLIMINDX.TAB in INDEX/ that summarizes key
information relevant to each observation, including which sequence
was in effect and what target was likely intended for the
observation.
Version
=======
This is VERSION 4.0 of this data set.
The pipeline (see Processing below) was re-run on these data for each
version since the first (V1.0). As a result, ancillary information,
such as observational geometry and time (SPICE), may be updated.
This will affect, for example, the calibration of the data if parameters
such as the velocity or orientation of the target relative to the
instrument, or the recorded target itself, have changed.
See the following sections for details of what has changed over each
version since the first (V1.0). Note that even if this is not a
calibrated data set, the calibration changes are listed as the data
will have been re-run and there will be updates to the calibration
files, to the documentation (Science Operations Center - Instrument
Interface Control Document: SOC_INST_ICD) and to the steps required
to calibrate the data.
SWAP updates for JUPITER
Data Sets V4.0
==============
The previous delivery (V3.0) went through peer review with many
Pluto Cruise data sets in December, 2014. When subsequent
versions of the latter were being delivered with additional data
(from August, 2015 through January, 2016) before all of those
liens were resolved, those data sets were left as is, with those
liens folded into the newer data sets. The same path was chosen
for this data set.
The changes for this version were re-running of the ancillary data
in the data product, updated geometry from newer SPICE kernels,
minor editing of the documentation, catalogs, etc., and resolution
of liens from the December, 2014 review, plus those from the May,
2016 review of the Pluto Encounter data sets. No new observations
were added with Version 4.0.
SWAP updates for Data Sets V3.0
===============================
About two-thirds of the products have been redelivered with changed
PRODUCT_IDs and new filenames; the data in those products will not have
changed significantly if at all. A table listing the new names and the
corresponding old names from the previous version has been provided in
the DOCUMENT/ subdirectory of this data set; refer to the PDS label of
that TABLE for more details. These changes are due to modifications
made to the file naming algorithms in the source data processing
pipeline software in the Science Operations Center (SOC).
Also, new versions of the SWAP spectrogram sample plots have been
generated and provided with this data set.
SWAP updates for Data Sets V2.0
===============================
New columns in REAL_TIME data extension
---------------------------------------
Added the center energy for given RPA and ESA voltages to the
REAL_TIME data extension. The column names are ENERGY_0 and
ENERGY_1 in eV and correspond to the 1st and 2nd measurement
in a given packet (row).
Calibration corrections
-----------------------
Corrected the background subtraction. Corrected a rounding
error in the time used to calculate the spin angles in the SPICE
extension and fixed a small offset in the times for the spectrogram
in the TIME_LABEL_SPECT extension.
Miscellaneous calibration corrections
-------------------------------------
Added 1-day and 10-day plots under the documents directory
in a folder called data_summary plots.
Processing
==========
The data in this data set were created by a software data
processing pipeline on the Science Operations Center (SOC) at
the Southwest Research Institute (SwRI), Department of Space Operations.
This SOC pipeline assembled data as FITS files from raw telemetry
packets sent down by the spacecraft and populated the data labels
with housekeeping and engineering values, and computed geometry
parameters using SPICE kernels. The pipeline did not resample
the data.
Data
====
The observations in this data set are stored in data files using
standard Flexible Image Transport System (FITS) format. Each FITS
file has a corresponding detached PDS label file, named according
to a common convention. The FITS files may have image and/or table
extensions. See the PDS label plus the DOCUMENT files for a
description of these extensions and their contents.
This Data section comprises the following sub-topics:
- Filename/Product IDs
- Instrument description
- Other sources of information useful in interpreting these Data
- Visit Description, Visit Number, and Target in the Data Labels
Filename/Product IDs
--------------------
The filenames and product IDs of observations adhere to a
common convention e.g.
SWA_0123456789_0X584_ENG.FIT
^^^ ^^^^^^^^^^ ^^^^^ ^^^\__/
| | | | ^^
| | | | |
| | | | +--File type (includes dot)
| | | | - .FIT for FITS file
| | | | - .LBL for PDS label
| | | | - not part of product ID
| | | |
| | | +--ENG for CODMAC Level 2 data
| | | SCI for CODMAC Level 3 data
| | |
| | +--Application ID (ApID) of the telemetry data
| | packet from which the data come
| | N.B. ApIDs are case-insensitive
| |
| +--MET (Mission Event Time) i.e. Spacecraft Clock
|
+--Instrument designator
Note that, depending on the observation, the MET in the data filename
and in the Product ID may be similar to the Mission Event Time (MET)
of the actual observation acquisition, but should not be used as an
analog for the acquisition time. The MET is the time that the data are
transferred from the instrument to spacecraft memory and is therefore
not a reliable indicator of the actual observation time. The PDS label
and the index tables are better sources to use for the actual timing of
any observation. The specific keywords and index table column names for
which to look are
* START_TIME
* STOP_TIME
* SPACECRAFT_CLOCK_START_COUNT
* SPACECRAFT_CLOCK_STOP_COUNT
Instrument Instrument designators ApIDs **
=========== ================================== =============
SWAP SWA 0X584 - 0X587 *
* Not all values in this range are in this data set
** ApIDs are case insensitive
There are other ApIDs that contain housekeeping values and
other values. See SOC Instrument ICD (/DOCUMENT/SOC_INST_ICD.*)
for more details.
Here is a summary of the types of files generated by each ApID
(N.B. ApIDs are case-insensitive) along with the instrument
designator that go with each ApID:
ApIDs Data product description/Prefix(es)
===== ===================================
0x584 - SWAP Science Real-Time/SWA
0x585 - SWAP Science Summary/SWA *
0x586 - SWAP Science Histogram Header/SWA
0x587 - SWAP Science Histogram Data/SWA
* Level 3 NH SWAP data sets produced after April, 2016 do not have 0x585
(Science Summary data); in-flight and in practice, 0x585 data are used
only for health and safety and not for science.
Instrument description
----------------------
Refer to the following files for a description of this instrument.
CATALOG
SWAP.CAT
DOCUMENTS
SWAP_SSR.*
SOC_INST_ICD.*
NH_SWAP_V###_TI.TXT (### is a version number)
Other sources of information useful in interpreting these Data
--------------------------------------------------------------
Refer to the following files for more information about these data
NH Trajectory tables:
/DOCUMENT/NH_MISSION_TRAJECTORY.* - Heliocentric
/DOCUMENT/NH_TRAJECTORY.* - Jupiter-centric
SWAP Field Of View definitions:
/DOCUMENT/NH_FOV.*
/DOCUMENT/NH_SWAP_V###_TI.TXT
SWAP Data summary plots:
/DOCUMENT/DATA_SUMMARY_PLOTS/SWAP_###DAY_YYYYMMDDHH_#.*
Visit Description, Visit Number, and Target in the Data Labels
---------------------------------------------------------------
The observation sequences were defined in Science Activity Planning
(SAP) documents, and grouped by Visit Description and Visit Number.
The SAPs are spreadsheets with one Visit Description & Number per row.
A nominal target is also included on each row and included in the data
labels, but does not always match with the TARGET_NAME field's value in
the data labels. In some cases, the target was designated as RA,DEC
pointing values in the form ``RADEC=123.45,-12.34'' indicating Right
Ascension and Declination, in degrees, of the target from the
spacecraft in the Earth Equatorial J2000 inertial reference frame.
This indicates either that the target was either a star, or that the
target's ephemeris was not loaded into the spacecraft's attitude and
control system which in turn meant the spacecraft could not be pointed
at the target by a body identifier and an inertial pointing value had
to be specified as Right Ascension and Declination values. PDS-SBN
practices do not allow putting a value like RADEC=... in the PDS
TARGET_NAME keyword's value. In those cases the PDS TARGET_NAME value
is set to CALIBRATION. TARGET_NAME may be N/A (Not Available or Not
Applicable) for a few observations in this data set; typically that
means the observation is a functional test so N/A is an appropriate
entry for those targets, but the PDS user should also check the
NEWHORIZONS:OBSERVATION_DESC and NEWHORIZONS:SEQUENCE_ID keywords in
the PDS label, plus the provided sequence list (see Ancillary Data
below) to assess the possibility that there was an intended target.
Ancillary Data
==============
The geometry items included in the data labels were computed
using the SPICE kernels archived in the New Horizons SPICE
data set, NH-X-SPICE-6-JUPITER-V1.0.
Every observation provided in this data set was taken as a part of a
particular sequence. A list of these sequences has been provided in
file DOCUMENT/SEQ_SWAP_JUPITER.TAB. In addition, the
sequence identifier (ID) and description are included in the PDS label
for every observation. N.B. While every observation has an associated
sequence, every sequence may not have associated observations. Some
sequences may have failed to execute due to spacecraft events (e.g.
safing). No attempt has been made during the preparation of this data
set to identify such empty sequences, so it is up to the user to
compare the times of the sequences to the times of the available
observations from INDEX/INDEX.TAB to identify such sequences.
Time
====
There are several time systems, or units, in use in this dataset:
New Horizons spacecraft MET (Mission Event Time or Mission Elapsed
Time), UTC (Coordinated Universal Time), and TDB Barycentric
Dynamical Time.
This section will give a summary description of the relationship
between these time systems. For a complete explanation of these
time systems the reader is referred to the documentation
distributed with the Navigation and Ancillary Information
Facility (NAIF) SPICE toolkit from the PDS NAIF node, (see
http://naif.jpl.nasa.gov/).
The most common time unit associated with the data is the spacecraft
MET. MET is a 32-bit counter on the New Horizons spacecraft that
runs at a rate of about one increment per second starting from a
value of zero at
19.January, 2006 18:08:02 UTC
or
JD2453755.256337 TDB.
The leapsecond adjustment (DELTA_ET = ET - UTC) was 65.184s at
NH launch, and the first three additional leapseconds occured
in at the ends of December, 2009, June, 2012 and June, 2015.
Refer to the NH SPICE data set, NH-J/P/SS-SPICE-6-V1.0, and the
SPICE toolkit docmentation, for more details about leapseconds.
The data labels for any given product in this dataset usually
contain at least one pair of common UTC and MET representations
of the time at the middle of the observation. Other portions
of the products, for example tables of data taken over periods
of up to a day or more, will only have the MET time associated
with a given row of the table.
For the data user's use in interpreting these times, a reasonable
approximation (+/- 1s) of the conversion between Julian Day (TDB)
and MET is as follows:
JD TDB = 2453755.256337 + ( MET / 86399.9998693 )
For more accurate calculations the reader is referred to the
NAIF/SPICE documentation as mentioned above.
Reference Frame
===============
Geometric Parameter Reference Frame
-----------------------------------
Earth Mean Equator and Vernal Equinox of J2000 (EMEJ2000) is the
inertial reference frame used to specify observational geometry items
provided in the data labels. Geometric parameters are based on best
available SPICE data at time of data creation.
Epoch of Geometric Parameters
-----------------------------
All geometric parameters provided in the data labels were computed at
the epoch midway between the START_TIME and STOP_TIME label fields.
Software
========
The observations in this data set are in standard FITS format
with PDS labels, and can be viewed by a number of PDS-provided
and commercial programs. For this reason no special software is
provided with this data set.
Contact Information
===================
For any questions regarding the data format of the archive,
contact
New Horizons SWAP Principal Investigator:
David McComas, Princeton University
David McComas
Princeton University
Princeton Plasma Physics Laboratory
Peyton Hall
Princeton, NJ 08544
USA
|
CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview
=========================
During the processing of the data in preparation for
delivery with this volume, the packet data associated with each
observation were used only if they passed a rigorous verification
process including standard checksums.
In addition, raw (Level 2) observation data for which adequate
contemporary housekeeping and other ancillary data are not available
may not be reduced to calibrated (Level 3) data. This issue is raised
here to explain why some data products in the raw data set,
NH-J-SWAP-2-JUPITER-V4.0,
may not have corresponding data products in the calibrated data set,
NH-J-SWAP-3-JUPITER-V4.0.
Data coverage and quality
=========================
Every observation provided in this data set was taken as a part of a
particular sequence. A list of these sequences has been provided in
file DOCUMENT/SEQ_SWAP_JUPITER.TAB. N.B. Some sequences
provided may have zero corresponding observations.
Refer to the Confidence Level Overview section above for a summary
of steps taken to assure data quality.
Observation descriptions in this data set catalog
=================================================
Some users will expect to find descriptions of the observations
in this data set here, in this Confidence Level Note. This data
set follows the more common convention of placing those
descriptions under the Data Set Description (above, if the user is
reading this in the DATASET.CAT file) of this data set catalog.
Caveat about TARGET_NAME in PDS labels and observational intent
===============================================================
A fundamental truth of managing data from some spacecraft missions
is that the intent of any observation is not suitable for insertion
into the command stream sent to the spacecraft to execute that
observation. As a result, re-attaching that intent to the data
that are later downlinked is problematic at best. For New Horizons
that task is made even more difficult as the only meta-data that
come down with the observation is the unpredictable time of the
observation. The task is made yet even more difficult because
uplink personnel, who generate the command sequences and initially
know the intent of each observation, are perpetually under
deadlines imposed by orbital mechanics and can rarely be spared for
the time-intensive task of resolving this issue.
To make a long story short, the downlink team on New Horizons has
created an automated system to take various uplink products, decode
things like Chebyshev polynomials in command sequences representing
celestial body ephemerides for use on the spacecraft to control
pointing, and infer from those data what the most likely intended
target was at any time during the mission. This works well during
flyby encounters and less so during cruise phases and hibernation.
The point to be made is that the user of these PDS data needs to
be cautious when using the TARGET_NAME and other target-related
parameters stored in this data set. This is less an issue for the
plasma and particle instruments, more so for pointing instruments.
To this end, the heliocentric ephemeris of the spacecraft, the
spacecraft-relative ephemeris of the inferred target, and the
inertial attitude of the instrument reference frame are provided
with all data, in the J2000 inertial reference frame, so the user
can check where that target is in the Field Of View (FOV) of the
instrument. Furthermore, for pointing instruments with one or more
spatial components to their detectors, a table has been provided
in the DOCUMENT/ area with XY (two-dimensional) positions of each
inferred target in the primary data products. If those values are
several thousand pixels off of a detector array, it is a strong
indication that the actual target of that observation is something
other than the inferred target, or no target at all e.g. dark sky.
Review
======
This dataset was peer reviewed and certified for scientific use on
2017-03-19.
|