| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This dataset contains raw clear-filter images of comet 103/P Hartley 2
acquired by the High Resolution Visible CCD (HRIV) from 05 September
through 26 November 2010 during the Hartley 2 encounter phase of the
EPOXI mission. Four color-filter sets (350-950 nm) were acquired
during the hour about closest approach. Initial results based on
these data are discussed by A'Hearn, et al. (2011) [AHEARNETAL2011].
The following list summarizes the comet observations in this dataset.
Descriptive text for each activity is included below. Additionally,
the HRIV Hartley 2 Flyby (E-18 hours to E+2 days) Log in the DOCUMENT
directory provides the imaging sequence and notes about image quality
that were recorded by the science team as the data arrived on the
ground.
--------------------------------------------------------------------------
Mid-Obs Exposure IDs Mission Activity
Date/DOY Min Max (E = Encounter)
-------------- ------- ------- ----------------------------------------
2010-09-05/248 4000000 4000009 Approach imaging E-60 to E-50 days;
to Rotation sampling every 6 hours;
2010-09-06/249 HRIV powered off after the first day*
2010-09-20/263 4000000 4000023 Approach imaging E-50 to E-40 days;
to HRIV turned on 5th day of this period;*
2010-09-25/268 Rotation sampling every 2 hours;
ExpIDs repeated daily;
2010-10-01/274 4000001 4000383 Approach imaging E-34 to E-8 days;
to Rotation sampling every 5 min;
2010-10-27/300 ExpIDs repeated daily**
2010-10-27/300 4000001 4000023 Approach imaging E-8 days to E-18 hours;
to Rotation sampling every hour;
2010-11-03/307 ExpIDs repeated daily***
2010-11-03/307 4000001 4000605 Flyby imaging E-18 to E-3 hours;
to Imaging every hour;
2010-11-04/308 ExpIDs are not repeated
2010-11-04/308 5000000 5007093 Flyby imaging E-2 to E+1.5 hours;
Imaging every 15 minutes to nearly
continuous at closest approach;
4 color filter sets;
ExpIDs are not repeated
2010-11-04/308 4000800 4009800 Flyby imaging E+2 hours to E+2 days;
to Imaging every hour;
2010-11-06/310 ExpIDs are not repeated
2010-11-06/310 4100000 4500002 Departure imaging E+2 to E+12 days;
to Rotation sampling every hour;
2010-11-16/320 ExpIDs repeated daily
2010-11-16/320 4100000 4500011 Departure imaging E+12 to E+21 days;
to Rotation sampling every 30 min;
2010-11-26/330 ExpIDs repeated daily
------------------------------------------------------------------------
* The HRIV instrument was turned off from 06 through 19 September
because of thermal issues with the baseplate of one of the
traveling wave tubes. No HRIV data were acquired during this
period.
** Data acquired on 06 Oct were never downlinked due to a pointing
problem with the Deep Space Network (DSN).
*** First cycle of 28 Oct, only six hourly scans were taken before the
sequence stopped and restarted at 'dosido' section for 7 hourly
scans. Therefore the middle 11 scans were not acquired on
purpose. Some frames in a scan may be missing because they were
scheduled for transmission after the HGA was turned off, i.e. loss
of signal. Any data the DSN received after this were considered
extra credit.
Hartley 2 Approach Imaging, E-60 to E-50 Days (VIS only): The MRI and
HRIV visible CCDs began imaging 103P/Hartley 2 every six hours on 05
September 2010, 60 days before the encounter (E-60 days) encounter
and continued for 10 days. However due to thermal issues with a
traveling wave tube amplifier the entire HRI system including the
HRIV CCD was turned off on 06 September until 20 September. MRI
continued its imaging sequence as planned through E-50 days. The
comet was observed for 16 hours at a time with 8 hours devoted to
downlinking the data.
Hartley 2 Approach Imaging, E-50 to E-40 Days (VIS only): From 15 to
25 September 2010, the imaging cadence for MRI increased to every
two hours. On 20 September the HRIV CCD was turned on, and it begin
imaging 103P/Hartley 2 once every two hours for the duration of the
period. The comet was observed for 16 hours at a time with 8 hours
devoted to downlinking the data.
Hartley 2 Approach Imaging, E-34 to E-8 Days (Start HRII): From 01
to 28 October 2010, MRI and HRIV imaged 103P/Hartley 2 about
every 5 minutes while the HRII spectrometer scanned for outbursts
once every 30 minutes. The instruments observed the comet for 16
hours per day allowing for 8 hours of downlinking; the same sequence
was repeated daily yielding one full cycle per day. Data from the
6th cycle on 06 October 2010 (DOY 279) were never downlinked because
of a pointing problem with the Deep Space Network. Those data had
to be erased on board the spacecraft to make room for the next daily
cycle and could not be recovered.
Hartley 2 Approach Imaging, E-8 Days to E-18 Hours: From 28 October
to 03 November 2010, the MRI and HRIV imaged 103P/Hartley 2
continuously and HRII scanned the comet about every hour for 16
hours per day allowing for 8 hours of downlinking punctuated by
hourly maneuvers, called dosido, to observe the comet. During this
imaging phase there was only a single downlink of all images with
zero margin; thus some images were occasionally lost as expected.
The first cycle (DOY 300/301) was abbreviated such that the first
comet-imaging session was only 6-hours long, followed by the
standard 8-hour dosido.
Hartley 2 Encounter Imaging, E-18 hours to E+2 Days: From 03 to 06
November 2010, the HRII, HRIV, and MRI performed high resolution
encounter imaging of 103P/Hartley2. The HRIV and MRI instruments
began sampling about once every two hours until one hour before
encounter when the cadence changed to once every 15 minutes. At E-30
minutes the instruments began continuously imaging of the comet. At
E+30 minutes simultaneous observing and data playback began with
samples being taken every 30 minutes. During the encounter imaging
period, HRII infrared scans occurred every two hours until four hours
prior to encounter when the cadence increased to hourly then more
frequently one hour before closest approach. About one hour after
closest approach, regular infrared sampling at 30-minute intervals
resumed.
On 04 November near closest approach, HRIV obtained two, contiguous,
full color sets (350-950 nm) of images of the nucleus with a scale
< 50 m/pixel (the exposure IDs are provided):
5002031 - 5002038 (E-10 min, Full Frame/Mode 1, at ~15 m/pixel)
5006048 - 5006054 (E+09 min, Full Frame/Mode 1, at ~14 m/pixel)
Also on 04 November, HRIV obtained broadband, clear-filter images of
the nucleus with a scale < 10 m/pixel:
5004005 (E-3 min, Full Frame/Mode 1, at ~5 m/pixel)
5004008 (E-2.5 min, Full Frame/Mode 1, at ~4 m/pixel)
5004009 (E-2.5 min, Full Frame/Mode 1, at ~4 m/pixel)
5006011 (E+3 min, Full Frame/Mode 1, at ~4 m/pixel)
5006012 (E+3 min, Full Frame/Mode 1, at ~4 m/pixel)
5006015 (E+3.5 min, Full Frame/Mode 1, at ~5 m/pixel)
Please note the comet is in fewer HRIV frames than expected at
closest approach because there was an error in how the spacecraft was
commanded to point during closest approach. However this unexpected
offset enabled serendipitous imaging of cometary debris near the
nucleus.
Hartley 2 Departure Imaging, E+2 to E+12 Days: From 06 to 16 November
2010, the HRII spectrometer scanned 103P/Hartley 2 every ~15 minutes
while the MRI CCD imaged the comet every 2 minutes and HRIV once
every hour.
Hartley 2 Departure Imaging, E+12 to E+21 Days: From 16 to 26 November
2010, the HRII spectrometer scanned 103P/Hartley 2 every 30 minutes,
and HRIV performed rotation sampling at the same cadence. MRI
performed rotation sampling every 30 minutes and imaging using gas
filters every two to four hours.
Required Reading
---------------
The documents listed below are essential for the understanding and
interpretation of this dataset. Although a copy of each document is
provided in the DOCUMENT directory of this dataset, the most recent
version is archived in the Deep Impact and EPOXI documentation set,
DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V3.0, available online at
http://pds.nasa.gov.
EPOXI_SIS.PDF
- The Archive Volume and Data Product Software Interface
Specifications document (SIS) describes the EPOXI datasets, the
science data products, and defines keywords in the PDS labels.
HARTLEY2_CAL_PIPELINE_SUMM.PDF
- The EPOXI Hartley 2 Calibration Pipeline Summary provides an
overview the calibration pipeline as of June 2011 used for
processing data acquired during the Hartley 2 Encounter.
The document also discusses known limitations of the calibration
pipeline with respect to the HRII, HRIV, and MRI instruments.
For a thorough discussion of the pipeline refer to EPOXI
Instrument Calibration by Klaasen, et. al. (2011, in
preparation) [KLAASENETAL2011].
INSTRUMENTS_HAMPTON.PDF
- The Deep Impact instruments paper by Hampton, et al. (2005)
[HAMPTONETAL2005] provides very detailed descriptions of the
instruments.
HRIV_HARTLEY2_FLYBY_LOG.PDF
- This log provides notes recorded by the science team as each
Flyby exposure (scan) acquired from E-18 to E+48 hours was
received on the ground. Annotations include data quality and
a list of frames within each scan that appeared to contain the
comet.
HRIV_2_EPOXI_HARTLEY2.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 dataset. This file is very useful for determining which
data files to work with.
Related Data Sets
-----------------
The following PDS datasets are related to this one and may be useful
for calibration purposes:
DIF-C-HRIV-3/4-EPOXI-HARTLEY2-V1.0
- Calibrated HRIV images of comet Hartley 2
DIF-CAL-HRIV-2-EPOXI-CALIBRATIONS-V2.0
- Raw HRIV in-flight calibrations from 2007 to 2011
DIF-C-HRII-2-EPOXI-HARTLEY2-V1.0
DIF-C-HRII-3/4-EPOXI-HARTLEY2-V1.0
- Raw and calibrated HRII spectral images of Hartley 2
DIF-C-MRI-2-EPOXI-HARTLEY2-V1.0
DIF-C-MRI-3/4-EPOXI-HARTLEY2-V1.0
- Raw and calibrated MRI images of comet Hartley 2
DIF-C/E/X-SPICE-6-V1.0
- EPOXI SPICE kernels
DIF-CAL-HRII/HRIV/MRI-6-EPOXI-TEMPS-V2.0
- 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
DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V3.0
- Deep Impact and EPOXI documentation set including a draft of the
Deep Impact instrument calibration paper by Klaasen, et al. (2008)
[KLAASENETAL2006]
Processing
==========
The raw two-dimensional FITS CCD 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 EPOXI SIS document. The SDC
did not apply any type of correction or decompression algorithm to the
raw data.
Data
====
FITS Images and PDS Labels
--------------------------
Each raw HRIV image is stored as FITS. The primary data unit contains
the two-dimensional CCD image. It 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.
Each FITS file is accompanied by a detached PDS data label. The
EPOXI SIS document provides definitions for the keywords found in
a PDS data label. Many values in a label were extracted from
FITS image header keywords which are defined in the document
EPOXI_FITS_KEYWORD_DESC.ASC found in the Deep Impact and EPOXI
documentation dataset, DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V3.0.
File Naming Convention
----------------------
The naming convention for the raw data labels and FITS files is
HVyymmddhh_eeeeeee_nnn.LBL or FIT where 'HV' identifies the HRIV
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 or frames can be commanded for one
exposure ID. 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 6
frames were commanded for a scan with an exposure ID of 4000001, the
first FITS file name would be HV10090513_4000001_001.FIT and the last
would be HV10090513_4000001_006.FIT.
Image Compression
-----------------
For some HRIV frames the raw data numbers were compressed on board
the flyby spacecraft by use of a lookup table then downlinked,
processed, and archived in the same format. 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. See the EPOXI SIS and EPOXI Hartley 2 Calibration Pipeline
Summary documents as well as Klaasen, et al. (2008) [KLAASENETAL2006]
for more information.
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
the EPOXI SIS document.
Instrument Alignment
--------------------
For a comparison of the field of view and the relative boresight
alignment of HRIV to the Medium Resolution Instrument Visible CCD
(MRI) and the slit of the High Resolution IR Imaging Spectrometer
(HRII), see the instrument alignment section of the EPOXI SIS
document or Klaasen, et al. (2011) [KLAASENETAL2011].
Parameters
==========
Data Units
----------
Raw image data are in units of raw data numbers.
Imaging Modes
-------------
A summary of the imaging modes is provided here. For more
information see the EPOXI SIS and EPOXI Hartley 2 Calibration
Pipeline Summary documents, Hampton, et al. (2005) [HAMPTONETAL2005]
and Klaasen, et al. (2011) [KLAASENETAL2011].
X-Size Y-Size
Mode Name (pix) (pix) Comments
---- ------ ------ ------ ---------------------------------------
1 FF 1024 1024 Full frame, shuttered
2 SF1 512 512 Sub-frame, shuttered
3 SF2S 256 256 Sub-frame, shuttered
4 SF2NS 256 256 Sub-frame, not shuttered
5 SF3S 128 128 Sub-frame, shuttered
6 SF3NS 128 128 Sub-frame, not shuttered
7 SF4O 64 64 Sub-frame, not shuttered
8 SF4NO 64 64 Sub-frame, not shuttered, no overclocks
9 FFD 1024 1024 Full-frame diagnostic, shuttered
All modes are unbinned. Most image modes have a set of bias
overclock rows and columns, located around the edges of the image
array. All overclock pixels were excluded from the calculation of
the values for MINIMUM, MAXIMUM, MEDIAN, and STANDARD_DEVIATION in
the data labels. These overclock areas described in the Deep
Impact instruments document and the Deep Impact instrument
calibration document.
Filters
-------
A summary of the MRI filters is provided here. For more information
see the EPOXI SIS and EPOXI Hartley 2 Calibration Pipeline Summary
documents, Hampton, et al. (2005) [HAMPTONETAL2005] and Klaasen, et
al. (2011) [KLAASENETAL2011].
Filter Center Width
# Name (nm) (nm) Comments
- ---------- ----- ----- -------------------------------
1 CLEAR1 650 >700 Not band limited
2 BLUE 450 100
3 GREEN 550 100
4 VIOLET 350 100 Shortpass coating
5 IR 950 100 Longpass
6 CLEAR6 650 >700 Not band limited
7 RED 750 100
8 NIR 850 100
9 ORANGE 650 100
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
evaluated at the time light left the target that reached the
spacecraft at mid-obs time and the earth-observer-to-target values
evaluated at the time the light that left the target, which reached
the spacecraft at mid-obs time, reached Earth.
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. The kernels are archived in the
EPOXI SPICE dataset, 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 dataset 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
dataset.
|
| CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview
=========================
The FITS files in this dataset were reviewed internally by the EPOXI
project and were used extensively to verify the calibration of the
instrument.
Review
======
This dataset was peer reviewed and certified for scientific use on
15 August 2011.
Data Coverage and Quality
=========================
There are no unexpected gaps in this dataset, except those that
occurred 06-19 September and on 06 and 28 October 2011 as noted in the
dataset overview. All science frames received on the ground were
processed and included in this dataset.
Some frames (exposures IDs) in this dataset are repeatedly smeared
because the spacecraft was in motion due to an HRII spectrometer
scan.
Horizontal striping through some images indicates missing data. The
image quality map extension identifies where pixels are missing. If
the second most-significant bit of a pixel in the image quality map is
turned on, then data for the corresponding image pixel is missing. For
more information, refer to the EPOXI SIS document.
Limitations
===========
Timing
------
The flyby spacecraft clock SPICE kernels (SCLK) used to convert to
UTC and to calculate geometry-related parameters for this dataset
have a known accuracy of no better than 0.5 seconds. However the
latest SCLK (science version 84) applied to the Hartley 2 encounter
data is good to within 0.01 seconds for converting the spacecraft
timestamps to ephemeris time for observations acquired around
closest approach. Please note that the SCLK (version 65) used to
compute UTC values and geometry for calibration data acquired from
January 2009 through July 2010 has known discontinuities of up to a
second. Those discontinuities have been corrected in the latest
SCLK, science version 84, applied to Hartley data.
The mission operations team has figured out how to correct raw clock
correlation data for the Deep Impact flyby spacecraft to allow
timing fits that are accurate to well under the sub-second level as
evidenced by the 0.01-second accuracy around the time the Hartley 2
encounter. The EPOXI project plans to use this method to generate a
complete and highly accurate set of UTC correlations for the flyby
spacecraft since the launch, resulting 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 datasets for the two missions and posted on the
NAIF/SPICE web site at http://naif.jpl.nasa.gov/naif/. The EPOXI
project will provide more precise times for archived data as time
and funding permit.
HRI Telescope Focus
-------------------
Images of stars acquired early during the Deep Impact mission in
2005 indicated the HRI telescope was out of focus. In-flight
bakeouts during late February and early March 2005 reduced the
defocus from about 1.0 cm to about 0.6 cm, resulting in a decrease
in the width of stars from about 12 pixels to 9 pixels. For more
details, please see the Deep Impact instrument calibration paper by
Klaasen, et al. (2008) [KLAASENETAL2006] and the Deep Impact image
restoration paper by Lindler, et al. (2007) [LINDLERETAL2007].
CCD Horizontal Gap
------------------
Calibration analysis combining Deep Impact and early EPOXI data
determined the two halves of the HRIV CCD - the boundary being the
two horizontal central lines 511 and 512 (zero based) - while
physically consistent across the boundary, are 1/6 of a pixel
smaller vertically than a normal row. Therefore, reconstructed
images, which have uniform row spacing, have a 1/3-pixel extension
introduced at the center of the array. Thus for two features on
either side of the midpoint line, the vertical component of the
actual angular separation between those features is one-third of a
pixel less than their measured difference in vertical pixels in the
image. As for all geometric distortions, correction of this
distortion will require resampling of the image and an attendant
loss in spatial resolution. The standard pipeline process does
not perform this correction so as to preserve the best spatial
resolution.
The two 1/6-pixel narrower central rows collect only 5/6 of the
charge of a normal row. This effect is corrected by the flat-field
division for calibrated science images so that the pixels in these
rows have the correct scene radiance assigned to them. However,
point-source or disk-integrated photometric measurements using
aperture photometry areas that include these central rows will be
slightly distorted unless special adjustments are made. For
example, the aperture photometry process for comet 9P/Tempel 1 added
an extra 1/6-pixel worth of signal to the to the pixels in each of
these two rows in the reconstructed, calibrated images as described
in Appendix A of Belton, et al., (2011) [BELTONETAL2011].
Displaying Images
-----------------
Flight software writes an image header over the first 100 bytes of
quadrant A. These image header pixels were included in the raw
FITS images. Since the values in these pixels vary dramatically,
it is recommended that the values of the MINIMUM and MAXIMUM
keywords in the data label (or the MINPVAL and MAXPVAL in the FITS
header) be used to scale an image for display because these values
exclude the header bytes as well as the overclock rows and columns
located around the edge of the CCD image. For more information,
see the quadrant nomenclature section of the EPOXI SIS document.
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