| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains Raw data taken by New Horizons
Alice Ultraviolet Imaging Spectrograph
instrument during the PLUTO mission phase.
PERSI-Alice (P-ALICE; also ALICE) is a spectrograph on the New Horizons
spacecraft that is sensitive to extreme and far UltraViolet (UV) light
(520-1870 Angstroms). The ALICE instrument comprises a telescopic optics
section and a spectrograph section that includes a diffraction grating
and a photosensitive two-dimensional (2-D) detector. The optics and
diffraction grating physical arrangement configure one detector
dimension as a spatial dimension and the other as spectral. ALICE has
two separate entrance apertures that feed light to the telescope section
of the instrument: the AirGlow Channel (AGC) aperture; the Solar
Occultation Channel (SOCC) aperture. Both apertures pass light to the
detector through a lollipop-shaped slit comprising two contiguous
sections: a narrow, rectangular slit with a Field Of View (FOV) of 0.1
by 4.0 degrees; a fat, square slit with FOV 2.0 x 2.0 degrees. ALICE has
two data-taking modes: PixelList mode records each detector/photon
event location (pixel i.e. spectral and spatial), interleaved with time
sequence events (hacks), allowing sub-second resolution of the photon
events; histogram mode summarizes the per-pixel photon event counts into
a 2-D histogram over all detector pixels, collected over an extended
time which can range from a few seconds to several days. From both
modes, the common data product is the histogram (derived on the ground
in the PixelList case), which is functionally equivalent to a
spectral-by-spatial spectrogram (2-D image); other data products are
also provided and described in this data set.
During the Pluto Charon Encounter 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); a Transition sub-phase
closing out the encounter mission phase and ending in late October,
2016. For this final ALICE delivery for the Pluto mission phase, this
data set includes Approach, CORE, Departure, and Transition sequences'
data that was downlinked through late October, 2016.
The first Pluto dataset delivery for the P-Alice instrument covers the
data on the ground between 1/15/2015 and 7/31/2015. It includes
functional testing and preliminary observations made during approach,
as well as a selected few observations from the few days up to the
Pluto encounter closest approach. Rho_Leo and Alice_Func are instrument
functional and calibration tests. PC_AIRGLOW is an observation that was
repeated regularly over the 2 months leading up to the CORE sequence.
The VISUV_MAP, Multi_Map, Airglow_Appr, and Airglow_Held observations
are part of the prime science data sets that meet specific objectives
of the mission.
*--- Alice_Rho_Leo
This observation points the P-Alice airglow boresight to the sky
location of Rho Leo to meet the following objectives:
1) Quick flux sensitivity verification,
2) Airglow pointing verification,
3) Detector PHD determination.
There are the two observations included:
Unsaturated PHD observation, a single 30 second Histogram, and a
Rho-Leo observation, another single 300 second Histogram.
*--- Alice_Func_080
This observation is the standard functional wake up Check (HK-TM,
Modes, Checksums and Selftest) with the following objectives:
1) Verify some very basic operations after the instrument has been
deactivated for some period of time (>month),
2) Verify unchanged code (PROM and EEPROM),
3) Verify successful parameter load and values,
4) Verify successful completion of internal selftest,
5) Verify unchanged behavior of the pixelhack problem
6) Perform a standard door performance test run
*--- PC_AIRGLOW 2.1-1.4
This set of observations is the P-Alice airglow observation of Pluto in
histogram mode. Each observation includes 6, 600 second histograms with
Pluto and Charon in the long and narrow portion of the slit. If
you visualize the slit as being the shape of a lollipop, the long
and narrow portion of the slit would correspond to the stick of the
lollipop. This region is known as the 'slot'.
They meet a goal to determine the time variability of Pluto's surface
and atmosphere, and the airglow variability over several rotations. The
long-time base of this observation is to look for variability in
Pluto's atmosphere or excitation mechanisms. Deep histograms are
obtained roughly daily over a few set intervals on approach to document
and study the variability of atmospheric airglow emissions from H, O,
and N atoms/ions, N2 and CO band emissions, and to search for other
emissions such as from S, Ar, and Ne atoms. Pluto will not be resolved,
but it is possible that extended emission in the system could be seen,
though model brightness estimates indicate this is unlikely. Models
predict emission brightnesses of 0.01 to a few Rayleighs.
*--- PC_PIXELLIST
Functional test of P-Alice, with a few minutes of data using Pixel
list.
*--- UNOCC_SUN
Unocculted sun observation.
A series of different exposures, 1 histogram for each, at 1, 10, 100,
and 1000 seconds. This is a histogram instead of PixelList, but
otherwise, it uses the same orientation, observation setup, and same
instrument parameters (voltage, etc) as P_OCC.
*--- PC_VISUV_MAP
PEAL_01_PC_VISUV_MAP_B_12 is a 40 minute P-Alice Histogram on Pluto and
Charon in the P-Alice box, taken 15 days before closest approach. For
these types of observations taken less than 10 days before closest
approach, Pluto and Charon are targeted in the slot. The goal is: Color
and Composition of Non-Encounter Hemispheres of Pluto & Charon. The
scientific motivation is to document the rotational disk-integrated UV
lightcurves of Pluto and Charon, primarily for surface composition, and
to search for spectral features indicative of surface materials such as
H2O-ice. It is expected that only the longer wavelengths will have
small enough opacity to see Pluto's surface, based on current
(1992-2007) gaseous CH4 observations.
*--- PC_Multi_Map_A/B
Multi_Map_A5 has 4, 600 second P-Alice Airglow histograms with Pluto in
the box, similar to PC_VISUV_MAP. These observations are all multiple
300 second Airglow histograms, similar to PC_VISUV_MAP. For the
Multi_Map_B observations, Pluto is aligned in the center of the slot.
All of the PC_Multi_Map observations have the same goals as
PC_VISUV_MAP.
*--- PC_Airglow_Appr
There were 5 total of these observations, with Appr_3 and Appr_4 being
the last 2, taken a few hours before closest approach.
PC_Airglow_Appr_3 has 10, 300 second histograms, and PC_Airglow_Appr_4
has 18, 150 second histograms. They meet a number of primary mission
goals. In addition to the goals for PC_VISUV_MAP and PC_Multi_Map,
these measurements also can be used for Pluto/Charon Hemisphere Surface
Composition Maps, to determine Pluto's Atmospheric Composition (N2, CO,
CH4, Ar), and the secondary goal of searching for emissions from minor
species (e.g., H, or perhaps C) in the airglow spectra.
The observations provide the best practical S/N on the airglow and
information on its spatial distribution with both dayglow and
nightglow. Airglow observations from Pluto are very weak, but are
expected to provide the primary means for detecting certain minor
atmospheric species, including Ar and CO. Typical expected limb
brightnesses are a few Rayleighs or less, with the exception of H Lyman
alpha, which is expected to be 50-100 Rayleighs (note that this should
be darker than the background interplanetary signal from H Lyman alpha,
which should be ~100-200 Rayleighs). Most of these emissions are
excited by photoelectron impact (peaking in emission rate at ~1000 km
altitude), and modeling the observed emissions will yield density
estimates for the parent species. It is important to note that N+
emissions result from dissociation/ionization/excitation of N2, and
provide no information regarding Pluto's ionosphere.
The observations can also be used to generate Pluto- and
Charon-resolved UV surface maps. P-Alice is used for surface
composition studies of the sunlit face of Pluto, mostly looking for
H2O, and the instrument is used as a backup for LEISA composition
mapping. Water ice and certain other frosts have FUV absorption bands
that could be detected by making albedo maps. These observations can
also provide the disk-integrated rotationally resolved UV light curves
of Pluto and Charon, in support of surface composition studies.
Any additional Alice airglow or H Lyman alpha coronal data would be
useful for investigating atmospheric composition. Most of the near
encounter observations are designed for high-resolution surface
studies. Although the Alice instrument has poor spatial resolution, its
time-tagging ability makes it very flexible at taking useful data
whenever there is an opportunity (i.e., whenever MVIC, LEISA, or REX
are making primary observations).
*--- P_Alice_Airglow_Held
These observations are Alice airglow observations of Pluto in held
histogram mode, taken just before closest approach. Held_1 is 180
seconds, and Held_2 is 65 seconds. In addition to the goals from
PC_Airglow_Appr, these observations see the Pluto airglow at the limb.
As with the near-encounter airglow observations, these limb
observations are to ensure we obtain spatially-resolved airglow data.
At the bright limb, Pluto's airglow emissions should be ~10x brighter
due to the extended path length.
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_ALICE_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 3.0 of this data set.
The TARGET_NAME values were expanded and made more consistent across
all instruments with version 3.0 of the data set.
General statement about data set versions after V1.0
----------------------------------------------------
The pipeline (see Processing below) was re-run on these data for each
version since the first (V1.0). That will typically change only the
FITS headers but not the FITS data of raw data sets. In some cases
this may change the calibration because the calculated geometry of an
observation has changed. See data set version-specific sections below
for significant exceptions to this general statement, i.e. changes to
pipeline processing, calibration processing, and data delivered.
An all-instrument Calibration Campaign occurred in July 2016. For all
instruments, calibrations were updated as of April 2017 which changed
the data in the calibrated data sets. Calibration changes are described
in the data set version-specific sections.
Note that even if this is not a calibrated data set, 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.
ALICE updates for Pluto Encounter
Data Sets V3.0
==============
This P3 Pluto Encounter dataset release includes all data from the
previous two Pluto deliveries and adds data that was downlinked from
1/31/2016 through 10/31/2016. This dataset completes delivery of all
data covering the Pluto Encounter and subsequent Calibration Campaign.
It includes the additional observations below for ALICE:
Request ID|Obs. Start Time (S/C UTC)|Downlink Complete (GRT)|Obs. Target
PEAL_01_PC_Multi_Map_A_18 2015-188_15:59:23 2016-105T02:58:06 Pluto and Charon
PEAL_01_PC_Multi_Map_B_2 2015-189_07:59:23 2016-075T20:18:37 Pluto and Charon
PEAL_01_PC_Multi_Map_B_3 2015-189_16:01:23 2016-075T20:24:52 Pluto and Charon
PEAL_01_PC_Multi_Map_B_5 2015-190_02:47:53 2016-105T03:08:57 Pluto and Charon
PEAL_01_PC_Multi_Map_B_6 2015-190_15:50:23 2016-114T20:32:25 Pluto and Charon
PEAL_01_PC_Multi_Map_B_8 2015-191_07:52:23 2016-075T20:31:03 Pluto and Charon
PEAL_01_PC_Multi_Map_B_9 2015-191_15:53:23 2016-114T20:38:16 Pluto and Charon
PEAL_01_PC_Multi_Map_B_11 2015-192_02:51:23 2016-095T04:47:53 Pluto and Charon
PEAL_01_PC_Multi_Map_B_12 2015-192_15:43:33 2016-114T20:44:32 Pluto and Charon
PEAL_01_PC_LYMAP 2015-194_16:22:25 2016-058T00:04:40 Pluto and Charon
PEAL_01_N_Alice_Best 2015-195_06:53:50 2016-171T17:28:59 Nix
PEAL_01_H_LEISA_Best 2015-195_07:22:05 2016-171T17:24:19 Hydra
PEAL_01_C_LORRIDump 2015-195_08:39:07 2016-114T20:45:01 Charon
PEAL_01_P_LEISA_Alice_1a 2015-195_08:41:55 2016-066T07:28:53 Pluto
PEAL_01_P_LEISA_Alice_1b 2015-195_08:55:36 2016-066T09:06:38 Pluto
PEAL_01_C_LEISA_LORRI_1Dump 2015-195_09:25:09 2016-095T04:48:36 Charon
PEAL_01_P_LEISA_Alice_2a 2015-195_09:26:15 2016-066T16:52:12 Pluto
PEAL_01_P_LEISA_Alice_2b 2015-195_09:40:45 2016-066T18:39:22 Pluto
PEAL_01_P_Alice_StarOcc1 2015-195_15:51:51 2016-050T23:04:56 Pluto
PEAL_01_P_O_Ring_Oc2 2015-197_09:36:09 2016-272T03:54:47 Pluto
PEAL_01_O_Ring_OC3 2015-197_21:24:09 2016-189T17:33:00 Pluto
APAL701_Wakeup 2016-188_02:10:41 2016-191T16:01:51 Calibration
TRAL703_01_HV_Dark_Verification 2016-197_09:20:23 2016-206T12:30:56
Calibration
TRAL704_01_Ptn_Verif_RhoLeo 2016-197_12:59:52 2016-227T05:45:18 Rho Leo
TRAL705_01_Airglow_Eff_Area_RhoLeo 2016-197_14:32:56 2016-206T12:33:40 Rho Leo
TRAL705_01_Airglow_Eff_Area_HD93521 2016-197_16:24:56 2016-206T12:36:27
HD93521
TRAL706_01_SOCC_Eff_Area_Spica 2016-197_19:20:56 2016-206T12:38:14 Spica
Also, updates were made to the calibration files, documentation, and
catalog files. The data were re-run through the updated pipeline,
which changed the FITS headers of the raw data set, but not the FITS
data. The updated Effective Area calibration file (pa_aeff_007.tab)
changed the calibrated data.
As of V3.0, targets for some stars and radio sources have been updated
so that the TARGET_NAME keyword in the label is accurate and more
descriptive than only STAR or CALIBRATION. However the user should
confirm that targets from the data FITS files, if applicable for a
given instrument, match the label name, as there are a few instances
where the FITS keywords for TARGET, SPCCBTNM, and PNTMTHD are not
accurate. The simplest way to check is to instead look at the RA
and Dec in the keywords SPCBRRA and SPCBRDEC in the FITS file.
This issue mostly only occurs with star targets.
ALICE updates for Pluto Encounter
Data Sets V2.0
==============
This P2 Pluto Encounter dataset release provides updates to the Pluto
dataset between P1 (data on the ground by 7/31/2015) and P2 (data on
the ground by 1/31/2016). All liens from the initial Pluto delivery
have also now been resolved. For ALICE it contains only data from the
Pluto Encounter period. Of note, the Pluto and Charon occultations are
now included and can be found in the PEAL_01_Pocc, PEAL_01_PoccEgress,
and PEAL_01_Cocc observations. The start and stop MET's for these
observations are below (Name, Start MET, Stop MET)
PEAL_01_Pocc 299,182,045 299,184,153
PEAL_01_PoccEgress 299,184,311 299,186,689
PEAL_01_Cocc 299,187,716 299,191,645
The dataset includes the observations below in addition to those from
the initial Pluto delivery:
Obs. Name (Request ID), Obs Date, Downlink Start, Downlink End, Obs. Target
PEAL_01_Cocc 2015-07-14 2015/263 2015/346 Charon Occultation
PEAL_01_C_LEISA_HiResDump 2015-07-14 2015/292 2015/292 Charon observation
PEAL_01_O_UnOccSun 2015-07-14 2015/264 2015/264 Unocculted Sun Histograms
PEAL_01_O_UnOccSun_B 2015-07-15 2015/335 2015/335 Unocculted Sun Histograms
PEAL_01_PCNH_Multilong_1d1 2015-07-13 2015/292 2015/292 Pluto, Ch, Nix, Hyd
PEAL_01_PC_Airglow_Appr_1a 2015-07-13 2015/292 2015/292 Pluto and Charon obs
PEAL_01_PC_Airglow_Appr_1b 2015-07-14 2015/292 2015/292 Pluto and Charon obs
PEAL_01_PC_Airglow_Appr_2 2015-07-14 2015/292 2015/292 Pluto and Charon obs
PEAL_01_PC_Airglow_Fill_0 2015-07-13 2015/292 2015/292 Pluto and Charon obs
PEAL_01_PC_Airglow_Fill_2 2015-07-13 2015/292 2015/292 Pluto and Charon obs
PEAL_01_PC_Airglow_Fill_DOY174 2015-06-23 2015/247 2015/247 Pluto, Charon obs
PEAL_01_PC_Multi_Map_A_3 2015-07-02 2015/229 2015/229 Pluto and Charon obs
PEAL_01_PC_Multi_Map_A_7 2015-07-03 2015/226 2015/226 Pluto and Charon obs
PEAL_01_PC_VISUV_MAP_B_3 2015-06-26 2015/246 2015/246 Pluto and Charon obs
PEAL_01_PC_VISUV_MAP_B_6 2015-06-27 2015/244 2015/244 Pluto and Charon obs
PEAL_01_PC_VISUV_MAP_B_9 2015-06-28 2015/244 2015/244 Pluto and Charon obs
PEAL_01_Pocc 2015-07-14 2015/269 2015/272 Pluto Occultation
PEAL_01_PoccEgress 2015-07-14 2015/267 2015/275 Pluto Occultation
PEAL_01_P_Airglow_Dep_1 2015-07-14 2015/292 2015/292 Pluto observation
PEAL_01_P_Airglow_Dep_2 2015-07-15 2015/292 2015/292 Pluto observation
PEAL_01_P_Airglow_Dep_A_1 2015-07-16 2015/292 2015/292 Pluto observation
PEAL_01_P_Airglow_Dep_A_2 2015-07-17 2015/292 2015/292 Pluto observation
PEAL_01_P_Airglow_Dep_A_3 2015-07-18 2015/292 2015/292 Pluto observation
PEAL_01_P_Airglow_Dep_A_4 2015-07-19 2015/292 2015/292 Pluto observation
PEAL_01_P_Color_2 2015-07-14 2015/253 2015/253 Pluto observation
PEAL_01_P_LEISA_HiResDump 2015-07-14 2015/292 2015/292 Pluto observation
PEAL_01_P_LORRIDump 2015-07-14 2015/292 2015/292 Pluto observation
PEAL_01_P_LORRI_Alice_Dep_1 2015-07-14 2015/292 2015/292 Pluto observation
PEAL_01_P_LORRI_Alice_Dep_2 2015-07-14 2015/292 2015/292 Pluto observation
PEAL_01_P_LORRI_Alice_Dep_3 2015-07-15 2015/292 2015/292 Pluto observation
PEAL_01_P_LORRI_Alice_Dep_4 2015-07-15 2015/292 2015/292 Pluto observation
PEAL_01_X_PLASMAROLL_3 2015-07-14 2015/264 2015/264 Airglow Histogram
PEAL_02_PC_Airglow_Fill_2 2015-07-13 2015/292 2015/292 Pluto and Charon obs
PEAL_03_PC_Airglow_Fill_2 2015-07-13 2015/292 2015/292 Pluto and Charon obs
PEAL_04_PC_Airglow_Fill_2 2015-07-13 2015/292 2015/292 Pluto and Charon obs
PEAL_05_PC_Airglow_Fill_2 2015-07-13 2015/292 2015/292 Pluto and Charon obs
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.
ALI_0123456789_0X4B0_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 **
=========== ================================== =============
ALICE ALI 0X4B0 - 0X4B7 *
* 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)
===== ===================================
0x4b0 - ALICE PixelList Lossless (CDH 1)/ALI
0x4b1 - ALICE PixelList Packetized (CDH 1)/ALI
0x4b4 - ALICE PixelList Lossless (CDH 2)/ALI
0x4b5 - ALICE PixelList Packetized (CDH 2)/ALI
0x4b2 - ALICE Histogram Lossless (CDH 1)/ALI
0x4b3 - ALICE Histogram Packetized (CDH 1)/ALI
0x4b6 - ALICE Histogram Lossless (CDH 2)/ALI
0x4b7 - ALICE Histogram Packetized (CDH 2)/ALI
Notes:
------
1) CDH 1 and CDH 2 refer to the spacecraft redundant Command and Data
Handling systems in general, and here specifically to their
respective Solid State Recorders (SSRs) 1 and 2, where ALICE data
be stored and prepared for downlink. ALICE can send data to SSR
1 or to SSR 2, or, for mission-critical data, to both redundantly.
ALICE shares its channel to the SSRs with the Long-Range
Reconaissance Imager (LORRI), so both instruments cannot store
data simultaneously. ALICE has the capability to store histogram
data to instrument-internal storage, and to transfer it to the
SSR(s) later; such an operation is called a Held Histogram, and
it allows ALICE to take data at the same time that LORRI is taking
and writing data to the SSR(s).
2) Packetized and Lossless refer to the method used on-board to
convert raw, high-speed instrument data on the SSR to low-speed
data ready for downlink. The conversion process is generally
referred to as compression, even though Packetized conversion does
not reduce the data volume In practice, PixelList data always
use Packetized compression. Histogram data may use Packetized or
Lossless compression. Depending on the actual data contents,
Lossless compression reduces data volume by 60 to 90% or more;
for nominal science data a factor of 3 or more is normal.
Lossless compression is used whenever possible to reduce downlink
data volume. There is no difference, between Packetized and
Lossless compression, in the resultant FITS files after processing
by the Science Operations Center (SOC) data pipeline.
Instrument description
----------------------
Refer to the following files for a description of this instrument.
CATALOG
ALICE.CAT
DOCUMENTS
ALICE_SSR.*
SOC_INST_ICD.*
NH_ALICE_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
ALICE Field Of View definitions:
/DOCUMENT/NH_FOV.*
/DOCUMENT/NH_ALICE_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. 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.
These two keywords are especially useful for STAR targets as often
stars are used as part of instrument calibrations, and are
included as part of the sequencing description which is captured
in these keywords.
Specifically for ALICE observations, any observation that has an
observation description or sequence ID that includes the words dump
or held will usually have N/A as its target, but that indicates the
observation was actually taken as part of an earlier sequence and held
held locally in instrument memory (i.e. a Held Histogram; see the
Notes in the Data section below), and the Dump sequence represents the
commands that transferred the instrument data onto the spacecraft
Solid-State Recorders (SSRs). In the cases of Held Histograms, the
user should check the previous sequence in the sequence list. For
other cases note that if the characters _P_, _C_, or _PC_ are in the
sequence ID, then the intended target was likely Pluto, Charon, or
Pluto and Charon together, respectively.
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_ALICE_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. 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 occurred
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 documentation, 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 ALICE Principal Investigator:
Alan Stern, Southwest Research Institute
S. Alan Stern
Southwest Research Institute (SwRI)
Department of Space Studies
1050 Walnut Street, Suite 400
Boulder, CO 80302
USA
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| 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-ALICE-2-PLUTO-V3.0,
may not have corresponding data products in the calibrated data set,
NH-P-ALICE-3-PLUTO-V3.0.
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_ALICE_PLUTO.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.
The lollipop-shaped fuzz in images of some ALICE spectra, seen as high
signal levels at the box end of the slit around Hydrogen Lyman-alpha (H
Lya) wavelengths, is due to a characteristic of the detector and
aperture. To make the Micro Channel Plate (MCP) more sensitive to UV
light, it was coated with potassium bromide (KBr) photocathodes from
520 to 1180 Angstrom and with cesium iodide (CsI) photocathodes from
1250 to 1870 Angstrom. A vertical strip - a spectral band of 70
Angstrom centered at ~1216 Angstrom - of the MCP was masked and left
uncoated to reduce the sensitivity of the detector to H Lya
radiation. In the slit portion of the aperture (0.1deg wide x 4deg
high), the diffraction grating keeps the strong H Lya line within that
uncoated band. However, in the 2x2 degree box portion of the aperture
designed to capture the Sun during occultations, the H Lya spreads out
beyond the uncoated 70-Angstrom band over another ~55 Angstroms of more
sensitive photocathode-coated detector on either side. The quantum
efficiencies of the photocathode- coated surfaces are about an order of
magnitude more sensitive to sensitive to H Lya wavelengths than the
bare, uncoated MCP glass, which gives rise to high signal levels from
the box area of the slit i.e. the lollipop fuzz.
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
===============================================================
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 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.
Finally, note that, within the FITS headers of the data products,
the sequence tables, and other NH Project-internal documents used
in this data set and/or inserted into the data set catalog,
informal names are often used for targets instead of the canonical
names required for the TARGET_NAME keyword. For example, during
the Pluto mission phase, instead of the TARGET_NAME '15810 ARAWN
(1994 JR1)' there might be found any of the following: 1994JR1;
1994 JR1; JR1. For all values where the PDS keyword TARGET_NAME
is used (e.g. in PDS labels and in index tables), the canonical,
PDS-approved names are used (if not, please bring this to the
attention of PDS so it can be rectified). However, within the
context of this data set, these project abbreviations are not
ambiguous (e.g. there is only one NH target with 'JR1' in its
name), so there has been, and will be, no attempt to expand such
abbreviations where they occur outside formal PDS keyword values.
Review
======
This dataset was peer reviewed and certified for scientific use on
June 19, 2017.
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