| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains version 1.0 of raw calibration data
acquired by the High Resolution Infrared Spectrometer (HRII)
during the EPOXI mission. The data for this version were
collected from 04 October 2007 through 08 October 2008, during the
first cruise and EPOCh phases of the mission as well as the early
part of the second cruise phase. Future versions of this data set
will include calibrations acquired during the remaining part of
the second cruise phase and the 103P/Hartley 2 encounter phase of
the EPOXI mission.
The purpose of these data are to monitor the HRII spectrometer and
improve its calibration as needed. Therefore EPOXI calibration
activities for the instrument generally followed those designed for
Deep Impact. For example standard calibration targets continue to
include the Moon, 16 Cyg A, 47 Tuc, Beta Hyi, HD 79447, NGC 7027, Vega,
sky frames, and dark frames. For a detailed discussion of how these
data are used to calibrate the instrument, see the Deep Impact
instrument calibration publication by Klaasen, et al. (2008)
[KLAASENETAL2006]. The calibration observations for EPOXI are based
on those designed for Deep Impact which are discussed by Klaasen,
et al. (2005) [KLAASENETAL2005].
Phase and Exposure ID
Calibration Activity Obs Date/DOY Target Start Stop
---------------------------- -------------- -------- ------- -------
Cruise 1
Instrument Checkout 2007-10-04/277 Sky 1010100 1010107
Instrument Checkout Retest 2007-12-04/338 Sky 1010200 1010208
Lunar Calibration 2007-12-29/363 Moon 1000005 1070000
Standard Cruise Cal 2008-01-09/009 Beta Hyi 2000000 2000001
HD 79447 2000002 2000002
47 Tuc 2000003 2000004
Vega 2010000 2010001
16 Cyg A 2010002 2010003
Dark 2011000 2012010
NGC 7207 2012011 2012012
Dark Retake for Lunar Cal 2008-01-16/016 Dark 1000000 1000054
2008-01-17/017 Dark 1000005 1000154
EPOCh
Darks for Earth Obs #1 2008-03-18/078 Dark 1000000 1000001
2008-03-19/079 Dark 1002024 1002025
Darks for Earth Obs #4 2008-05-28/149 Dark 1000000 1000001
2008-05-29/150 Dark 1002024 1002025
Darks for Earth Obs #5 2008-06-04/156 Dark 1000000 1000001
2008-06-05/157 Dark 1002024 1002025
Standard Cruise Cal 2008-06-23/175 Vega 2010000 2010001
16 Cyg A 2010002 2010003
NGC 7207 2010004 2010005
Dark 2011000 2012020
2008-06-24/176 Beta Hyi 2000000 2000001
HD 79447 2000002 2000002
47 Tuc 2000003 2000004
Cruise 2
HRII Reciprocity Test 2008-09-18/262 Dark 3200000 3200019
HRII Dark Flush Test 2008-09-26/270 Dark 3000001 3000011
HRII Encounter Darks Rerun 2008-10-02/276 Dark 9000030 9020002
HRII Dark Gap Test 2008-10-08/282 Dark 3100000 3100024
Instrument Checkout: On 4 October the three science instruments
were turned on for the first time in more than two years. Sky
frames acquired by the HRII spectrometer confirmed the mechanical
components were functioning. The instrument exhibited nominal
behavior of background levels although several detector pixels had
an odd response when compared to Deep Impact.
Instrument Checkout Retest: On 4 December 2007 a retest of the
October instrument checkout sequence was performed for the three
science instruments. The focus of this retest was to determine if
HRII pixels that had an odd response during checkout had changed
or improved.
Lunar Calibration: On 29 December 2007 as the spacecraft approached
Earth, the three science instruments used the Moon as a target to
acquire data for recalibration purposes. Due to a minor error in
the lunar calibration sequence, a series of HRII dark frames were
not recorded. A retest to acquire the missing HRII darks was
scheduled for 16-17 January 2008.
Standard Cruise Calibration: On 9 January 2008, the first of the
standard cruise calibrations for the three science instruments was
performed. The calibration sequence included observations of
several standard stars, both solar analogs and hot stars with few
absorption lines in their spectra for absolute calibration of all
instruments, a stellar cluster for checking geometric distortion in
the cameras, and a planetary nebula for checking the wavelength
calibration of the spectrometer. This sequence was designed such
that it could be rerun, with few if any changes, after completion
of the EPOCh observations and then again just before and just after
the observing program for comet 103P/Hartley 2.
HRII Dark Retake for Lunar Cal: Due to a minor error in the lunar
calibration sequence that was executed in December, a series of HRII
dark frames was not recorded. However that sequence was successfully
rerun for the HRII spectrometer on 16-17 January 2008.
EPOCh Earth Obs Darks: At the beginning and end of each EPOCh Earth
observation period, HRII dark frames were acquired for calibration
purposes and included in this data set.
Standard Cruise Calibration: A second standard cruise calibration
was performed on 23-25 June 2008 for the HRII and HRIV instruments.
The sequence was very similar to that used for the calibration
performed on 9 January 2008, except the MRI instrument was turned
off because of thermal and telecommunication concerns.
HRII Reciprocity Test: On 18 September 2008, an HRII reciprocity
test was performed to determine the background signal level of the
READ and RESET frames of the IR spectrometer as a function of the
past history of integration delay times and the timing gap between
sets of frames using the diagnostic imaging mode (number 6). The
ultimate objective of this test along with the HRII Dark Flush, HRII
Dark Gap, and HRII Subframe Gain tests performed over the next four
months is to develop a more accurate model of the variation in the
background level of the IR spectrometer. Data from the HRII
Subframe Gain test performed in late January 2008 will be included
in version 2.0 of this data set.
HRII Dark Flush Test: On 26 September 2008, an HRII dark frame
flush test was performed to determine the type of IR spectrometer
instrument operation needed to remove all traces of the residual
(previous) image.
HRII Encounter Darks Rerun: On 02 October 2008 a set of HRII dark
frames for several exposure IDs from the Deep Impact Tempel 1
encounter sequence was acquired. The exposures were those acquired
from about 19 minutes before the impact with Tempel 1 through the
first few hours of lookback imaging.
HRII Dark Gap Test: On 10 October 2008, an HRII dark gap test was
performed to characterize the change in the residual image and the
dark level in the IR spectrometer as a function of wait time and
number of readouts after acquiring data in the subframe imaging
modes (numbers 2 and 3).
Required Reading
---------------
The following documents are essential for the understanding and
interpretation of this data set. Please note the most recent
version of these documents, including other formats such as ASCII
text, can be found in the Deep Impact and EPOXI documentation data
set, DI-C-HRII-HRIV-MRI-ITS-6-DOC-SET-V2.0.
EPOXI_SIS.PDF
- The Archive Volume and Data Product Software Interface
Specifications document (SIS) describes the the data set, the
science data products, and defines keywords in the PDS labels.
CALIBRATION_PAPER_DRAFT.PDF
- The Deep Impact instrument calibration paper by Klaasen, et al.
(2008) [KLAASENETAL2006] describes how the instruments were
calibrated for Deep Impact and similarly for EPOXI and explains
the calibration process used for both missions. The published
version should be available online in the Review of Scientific
Instruments by the American Institute of Physics. The EPOXI
archive provides only an incomplete draft.
INSTRUMENTS_HAMPTON.PDF
- The Deep Impact instruments paper by Hampton, et al. (2005)
[HAMPTONETAL2005] provides very detailed descriptions of the
instruments.
HRII_2_EPOXI_CALIBRATIONS.TAB
- This ASCII table provides image parameters such as the mid-obs
Julian date, exposure time, mission activity type, and
description or purpose for each observation (i.e., data product)
in this data set. This file is very useful for determining which
data files to work with.
Related Data Sets
-----------------
The following PDS data sets are related to this one and may be useful
for calibration purposes:
DIF-E-HRII-2-EPOXI-EARTH-V1.0
DIF-E-HRII-3/4-EPOXI-EARTH-V1.0
- Raw and calibrated HRII Earth observations
DIF-C-HRII-2-EPOXI-HARTLEY2-V1.0
DIF-C-HRII-3/4-EPOXI-HARTLEY2-V1.0
- Raw and calibrated HRII comet Hartley 2 observations (to be
delivered in 2011)
DI-C-HRII-HRIV-MRI-ITS-6-DOC-SET-V2.0
- Deep Impact and EPOXI documentation set
DIF-C/E/X-SPICE-6-V1.0
- EPOXI SPICE kernels
DIF-CAL-HRII/HRIV/MRI-6-EPOXI-TEMPS-V1.0
- HRII, HRIV, and MRI instrument thermal telemetry data for EPOXI
which may be useful for determining how temperature fluctuations
affect the science instruments, in particular the IR spectrometer
DIF-CAL-HRII-2-9P-CRUISE-V1.0
DIF-CAL-HRII-2-9P-ENCOUNTER-V1.0
- Deep Impact raw HRII calibrations data sets from 2005
DIF-CAL-HRII-2-GROUND-TV1-V1.0
DIF-CAL-HRII/HRIV-2-GROUND-TV2-V1.0
DIF-CAL-HRII/HRIV/MRI-2-GROUND-TV4-V1.0
- Deep Impact raw HRII pre-launch calibrations from 2002 and 2003
Processing
==========
The raw two-dimensional (wavelength and spatial/along-slit) FITS
spectral images and PDS labels in this data set were generated by the
Deep Impact/EPOXI data pipeline, maintained by the project's Science
Data Center (SDC) at Cornell University. The FITS data were assembled
from raw telemetry packets sent down by the flyby spacecraft.
Information from the embedded spacecraft header (the first 100 bytes of
quadrant A image data) was extracted and stored in the primary FITS
header. Geometric parameters were computed using the best available
SPICE kernels and the results were also stored in the FITS header. If
telemetry packets were missing, the corresponding pixels were flagged
as missing in the quality map included as a FITS image extension. The
quadrant nomenclature and the image quality map are described in the
Deep Impact instrument calibration document and the EPOXI SIS document
included in this data set. The SDC did not apply any type of
correction or decompression algorithm to the raw data.
Data
====
FITS Images and PDS Labels
--------------------------
Each raw spectral image is stored as FITS. The primary data unit
contains the two-dimensional spectral image, with the fastest
varying axis corresponding to increasing wavelengths from about
1.05 to 4.8 microns and the slowest varying axis corresponding to
the spatial or along-slit dimension. The primary array is
followed by one image extension that contains a two-dimensional
pixel-by-pixel quality map. This extension uses one byte of eight
bit flags to indicate the quality of each pixel in the primary
image. The data label provides a short description of each bit.
For more information about the FITS primary image and its
extension or for examples of how to access and use the quality
flags, refer to the EPOXI SIS document or the Deep Impact
instrument calibration document.
Each FITS file is accompanied by a detached PDS data label. The
EPOXI SIS document provides definitions for the keywords found in a
data label.
File Naming Convention
----------------------
The naming convention for the raw data labels and FITS files is
HIyymmddhh_eeeeeee_nnn.LBL or FIT where 'HI' identifies the HRII
instrument, yymmddhh provides the UTC year, month, day, and hour at
the mid-point of the observation, eeeeeee is the exposure ID
(OBSERVATION_ID in data labels), and nnn provides the image number
(IMAGE_NUMBER in the data labels) within the exposure ID.
Up to 999 individual images can be commanded for one exposure ID.
Spectral scans often had 32 or more frames for one specific exposure.
Therefore, nnn in the file name provides the sequentially increasing
frame number within an exposure ID and corresponds to IMAGE_NUMBER in
the data labels. For example, if 32 frames were commanded for a scan
with an exposure ID of 1000001, the first FITS file name would be
HI08060416_1000001_001.FIT and the last would be
HI08060416_1000001_032.FIT.
Image Compression
-----------------
Although raw data numbers for HRII frames could be compressed on
board the flyby spacecraft by use of a lookup table then downlinked,
processed, and archived in the same format, all calibration-related
spectra acquired during the time period covered by this data set
were never compressed. A compressed image is identified by the
value 'COMPRESSED' in the COMPRESSED_IMAGE_VALUE keyword in the data
labels or the COMPRESS keyword in the FITS headers. For more
information about this topic, see the image compression section of
the Deep Impact instrument calibration documents.
Image Orientation
-----------------
A true-sky 'as seen by the observer' view is achieved by displaying
the image using the standard FITS convention: the fastest-varying
axis (samples or wavelength) increasing to the right in the display
window and the slowest-varying axis (lines or spatial/along-slit)
increasing to the top. This convention is identified in the data
labels: the SAMPLE_DISPLAY_DIRECTION keyword is set to RIGHT and
LINE_DISPLAY_DIRECTION to UP.
The direction to celestial north, ecliptic north, and the Sun is
provided in data labels by CELESTIAL_NORTH_CLOCK_ANGLE,
ECLIPTIC_NORTH_CLOCK_ANGLE, and SUN_DIRECTION_CLOCK_ANGLE keywords
and are measured clockwise from the top of the image when is
displayed in the correct orientation as defined by
SAMPLE_DISPLAY_DIRECTION and LINE_DISPLAY_DIRECTION. Please note
the aspect of the North celestial pole in an image can be computed
by adding 90 degrees to the boresight declination given by
DECLINATION in the data labels.
For a comparison of the orientation FITS image data from the three
science instruments, see the quadrant nomenclature section of the
Deep Impact instrument calibration document. Also the EPOXI SIS
has a brief discussion of this topic.
IR Slit Location
----------------
For a comparison of the relative locations of the IR slit with
respect to the fields of view of the Medium Resolution Instrument
Visible CCD (MRI) and the High Resolution Instrument Visible CCD
(HRIV), see the relative boresight alignments section of the
Deep Impact instrument calibration document.
Timing for Spectra
------------------
It is important to note that the readout order of the IR detector
affects the timing of the spectra. When a HRII spectral image is
displayed using the true-sky convention, the wavelength increases
horizontally to the right and the spatial or along-slit direction
is vertical. In this orientation, the IR detector was read out
from the left and right edges and toward the center and starting
with the first row at the bottom and ending with the last row at
the top of the display. Since the detector is reset and read out
on a pixel-by-pixel basis, the read out order affects the time at
which each pixel is exposed, although each pixel has the same
exposure duration. Additionally, the end of the spectrometer slit
that always points roughly towards the sun is the first line to be
readout and the last line to be read out is furthest from the sun,
assuming the spacecraft is in its usual orientation with the solar
pointing roughly toward the sun. For more information about the
timing of the spectra, see the IR focal plane and quadrant
nomenclature sections of the Deep Impact instrument calibration
document.
Parameters
==========
Data Units
----------
Raw image data are in units of raw data numbers.
Target Name and Description
---------------------------
The TARGET_NAME keyword in the data labels is set to the intended
target, 'CALIBRATION', for each observation in this data set. The
TARGET_DESC keyword provides the name of the specific calibration
target, such as 'DARK' or 'VEGA'.
Imaging Modes
-------------
For a thorough description of the imaging modes, please see the
Deep Impact instruments document or the Deep Impact instrument
calibration document. Also the EPOXI SIS has a brief discussion of
this topic. A summary of the imaging modes is provided here. In
the table below, X-Size is the spectral dimension and Y-Size is the
spatial dimension.
X-Size Y-Size Bin
Mode Name (pix) (pix) Type Comments
---- ------ ------ ----- ----- ---------------------------------
1 BINFF 512 256 2x2 Binned full frame
2 BINSF1 512 126 2x2 Binned sub-frame
3 BINSF2 512 64 2x2 Binned sub-frame
4 UBFF 1024 512 1x1 Unbinned full frame
5 ALTFF 512 256 2x2 Alternate mode 1 (min. exposure
time is 1/2 of mode 1)
6 DIAG 1024 512 1x1 Diagnostic, one reset frame
followed by a separate read frame
7 MEMCK 1024 512 1x1 Memory Check
Time- and Geometry-Related Keywords
-----------------------------------
All time-related keywords in the data labels, except
EARTH_OBSERVER_MID_TIME, are based on the clock on board the flyby
spacecraft. EARTH_OBSERVER_MID_TIME provides the UTC when an
Earth-based observer should have been able to see an event recorded
by the instrument.
The SDC pipeline was not able to automatically determine the proper
geometric information for the target of choice in some cases. When
these parameters could not be computed, the corresponding keywords
in the data labels are set to a value of unknown, 'UNK'. Also if
GEOMETRY_QUALITY_FLAG is set to 'BAD' or GEOMETRY_TYPE is set to
'PREDICTED' in the PDS labels, then this indicates the geometry
values may not be accurate and should be used with caution. The
value 'N/A' is used for some geometry-related keywords in the data
labels because these parameters are not applicable for certain
calibration targets.
Observational geometry parameters provided in the data labels were
computed at the epoch specified by the mid-obs UTC, IMAGE_MID_TIME,
in the data labels. The exceptions are the target-to-sun values
that were calculated for the time when the light arrived at the
target and the earth-observer-to-target values that were calculated
for the time when the light left the target.
The flyby spacecraft clock SPICE kernels (SCLK) used to convert to
UTC and to calculate geometry-related parameters for this data set
have a known accuracy of no better than 0.5 seconds. However as
this data set was being produced, the mission operations team
figured out how to correct raw clock correlation data for the
flyby spacecraft to allow timing fits that are accurate to at
least the sub-second level. The project plans to generate a
complete, corrected set of correlations since launch. This will
ultimately result in a future version of a SCLK kernel that will
retroactively change correlation for **all** Deep Impact and EPOXI
data. When this kernel is available, it will be added to the
SPICE data sets for the two missions and posted on the NAIF/SPICE
web site at http://naif.jpl.nasa.gov/naif/.
Ancillary Data
==============
The geometric parameters included in the data labels and FITS headers
were computed using the best available SPICE kernels at the time the
data products were generated. NAIF used these kernels to produce the
EPOXI SPICE data set, DIF-C/E/X-SPICE-6-V1.0.
Coordinate System
=================
Earth Mean Equator and Vernal Equinox of J2000 (EME J2000) is the
inertial reference system used to specify observational geometry
parameters in the data labels.
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.
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