| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains Calibrated data taken by New Horizons
Linear Etalon Imaging Spectral Array
instrument during the PLUTO mission phase.
LEISA is an infrared imaging spectrometer. The two-dimensional (2-D)
detector is a 256x256-pixel array. Spectral separation is done with a
wedged optical etalon filter, which comprises high (2.1-2.25 micron) and
low (1.225-2.5 micron) spectral resolution segments. The optics and
filter arrangement configure one detector dimension as spatial at
constant wavelength and the other dimension as both spectral and
spatial. Multiple frames (images) may be taken in sequence, while
scanning the Field Of View (FOV) in the spatial+spectral dimension, such
that each pixel-sized piece of the observed target will be observed at
all wavelengths across multiple frames. The resulting data products in
this data set are three-dimensional image cubes, which dimensions are
spatial, spatial+spectral, and spatial+time and which shall be convolved
into spatial, spatial, and spectral image cubes at a later date.
During the Pluto mission phase starting in January, 2015, there were
several sub-phases: three Approach sub-phases, (AP1, AP2 and AP3); a
CORE sequence for the Pluto flyby on 14.July, 2015 (Day Of Year 195),
sometimes also referred to as NEP (Near-Encounter Phase); three
Departure sub-phases (DP1, DP2, DP3). For this first Ralph-LEISA
delivery for the Pluto mission phase, this data set includes only the
Approach data plus the subset of the CORE sequence data that was
downlinked through the end of July, 2015. The rest of the Pluto data
will be delivered in future versions of this data set according to the
schedule worked out by the Project and NASA.
On Approach during April, May and June of 2015, LEISA operations
included the following: functional testsincluding a scan test; and
observations of Pluto, Charon and the other Plutonian satellites.
This dataset includes the first 3 P-LEISA scans of Pluto taken at 28,
26, and 24 days before the Pluto closest approach, to look for changes
in surface color and composition over multiple rotations. It also
includes three of the PC_VISUV_MAP observations at 18, 17, and 15 days
before encounter, with the same goal as P-LEISA. At 13 days,
PC_LEISA_VAR looks at the IR variability of Pluto and Charon.
The dataset also has a series of PC_MULTI_MAP observations, from 11
days and 2 days before closest approach. The PC_MULTI_MAPs met multiple
objectives as measurements coordinated with the P-Alice, LORRI, and
MVIC instruments. For LEISA, these objectives included determining
Pluto and Charon phase integrals, as LEISA offers another alternative
to visible wavelength imaging to get the angular dependence of
scattering by Pluto. They also are the primary method of performing
global temperature mapping of Pluto's surface ices, based on LEISA
near-IR spectral-imaging. The measurements support further goals for IR
spectroscopic maps of Pluto and Charon, searching for changes over
multiple rotations, looking at the composition of low albedo areas of
Pluto, and investigating the composition of non-encounter hemispheres
of Pluto and Charon. Also, using LEISA to observe various regions of
Pluto at or near the approach and departure asymptote phase angles
supports the determination of the bolometric albedos of various
regions. Finally, LEISA spectral studies of Pluto at multiple phase
angles helps to learn about surface processing and structure in various
regions.
The remainder of the LEISA dataset has 2 observations on the day of
closest approach: (1) P_LEISA_Alice_1a, which is a backup for scans of
whole disk at 7-10 km/pix to get a global infrared spectral map of
Pluto; and (2) C_LEISA_LORRI_1, which gives the Charon resolved IR
surface map and phase integral, and spectral studies of Charon at
multiple phase angles to learn about surface processing and structure
in various regions. Both also fulfill the objectives of the MULTI_MAPs.
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_LEISA_PLUTO.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 1.0 of this data set.
Processing
==========
The data in this data set were created by a software data
processing pipeline on the Science Operation Center (SOC) at
the Southwest Research Institute (SwRI), Department of Space Studies.
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.
Calibration
===========
Detailed information about calibration of LEISA data is available
in the SOC Instrument Interface Control Document (ICD) in the
DOCUMENT section of this data set. The LEISA calibration will only
be briefly summarized here; refer to the ICD for details about
what is summarized here.
The calibration of MVIC images comprises the following steps:
1) Remove electronics-induced and flat-field signal
2) Apply calibration offset and gain
3) Adjust for integration time, filter width, and pixel solid angle
4) Correct for gain
In addition, the calibration procedure calculates various quantities
such as error (see note below) and a data quality flag for each pixel
and includes those results in the calibrated data product as additional
PDS OBJECTs (FITS extensions) appended to the main OBJECT with the data
image. The quality flag PDS OBJECT is an image of values of the same
size as the main IMAGE product, with each quality flag pixel mapped to
the corresponding pixel in the main product. A quality flag value of
zero indicates a valid pixel; a non-zero value indicates an invalid
pixel.
Note that for windowed products, all pixels in an image are not
returned in the downlink telemetry. In the raw data, the pipeline
sets such pixels to zero DN (Data Number); the calibration processes
those zero-DN pixels as if they were real raw values may result in a
confusing result with the majority of the displayed image appearing as
an inverse of the calibration (calibration of zero values); therefore
the windowed status of the image, as recorded in the value for the NOTE
keyword of the PDS label should be considered when looking at these
data.
Calibration and data characteristics
------------------------------------
i) Error estimates are all zero. As of late 2014, the code to calculate
the values for the Error estimates extension has not been deployed to
the SOC, and placeholder code sets all pixel error estimates to zero.
When the updated code is deployed to the SOC, some reprocessed
observations may be delivered to PDS (e.g. Jupiter encounter data);
note that observations from the Launch and Pluto Cruise mission
phases have little if any science utility, so there is no incentive
to reprocess those data just to provide error estimates.
ii) Fixed-pattern noise. There is usually fixed-pattern noise (FPN) in
the data that cannot be removed by the flat-field correction. Users
need to generate an average of a few run-up frames containing
background sky and the FPN, and subtract that average from every
frame with a target source present. The number of frames to use
will vary by observation, so this operation is not part of the
automated pipeline.
iii) Scattered light. Although some observations have been taken to
characterize scattered light, no photometric modeling of the stray
light has been made or applied to the data. Those observations have
only been used to optimize the planned imaging at Pluto encounter to
minimize the effect of stray light.
Ongoing in-flight calibration observations will be analyzed to
assess the long term stability of the calibration.
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.
LSB_0123456789_0X53C_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
| |
| +--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
=========== ================================== =============
LEISA LSB, LRW 0X53C - 0X54E *
* Not all values in this range are in this data set
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 meanings of each instrument designator:
Instr
Dsgn. Description
===== ===========
LSB LEISA, Read minus Reset data
LRW LEISA, Raw Read and Reset data
See SOC Instrument ICD (/DOCUMENT/SOC_INST_ICD.*) for details
Here is a summary of the types of files generated by each ApID
along with the instrument designator that go with each ApID:
ApIDs Data product description/Prefix(es)
===== ===================================
0x53c - LEISA Lossless (CDH 1)/LRW,LSB
0x54b - LEISA Lossless (CDH 2)/LRW,LSB
0x53d - LEISA Packetized (CDH 1)/LRW,LSB
0x54c - LEISA Packetized (CDH 2)/LRW,LSB
0x53e - LEISA Lossy (CDH 1)/LRW,LSB
0x54d - LEISA Lossy (CDH 2)/LRW,LSB
Instrument description
----------------------
Refer to the following files for a description of this instrument.
CATALOG
LEISA.CAT
DOCUMENTS
RALPH_SSR.*
SOC_INST_ICD.*
NH_RALPH_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
RALPH Field Of View definitions:
/DOCUMENT/NH_FOV.*
/DOCUMENT/NH_RALPH_V###_TI.TXT
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. The PDS
standards 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.
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-PLUTO-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_LEISA_PLUTO.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; that is,
some sequences may have failed to execute due to spacecraft events
(e.g. safing) and there will be observations associated with those
sequences. No attempt has been made during the preparation of this
data set to identify if any, or how many, such empty sequences there
are, so it is up to the user to compare the times of the sequences
to the times of the available observations from the INDEX/INDEX.TAB
table 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) over this dataset
is 65.184s.
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 RALPH Principal Investigator:
Alan Stern, Southwest Research Institute
S. Alan Stern
Southwest Research Institute
Department of Space Studies
1050 Walnut Street, Suite 400
Boulder, CO 80302
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-P-LEISA-2-PLUTO-V1.0,
may not have corresponding data products in the calibrated data set,
NH-P-LEISA-3-PLUTO-V1.0.
Data coverage and quality
=========================
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
TBD.
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