DATA_SET_DESCRIPTION |
Data Set Overview
=================
This dataset contains calibrated 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 4000607 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 to hours 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_3_4_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-2-EPOXI-HARTLEY2-V1.0
- Raw 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 calibrated 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 version of the pipeline used to calibrate these data
was the best available as of June 2011. Known limitations and
deficiencies of the pipeline and the resulting data are discussed in
the EPOXI Hartley 2 Calibration Pipeline Summary document in this
dataset or by Klaasen, et al. (2011, in preparation) [KLAASENETAL2011].
For each CCD image, the pipeline generates two types of calibrated
products:
- Uncleaned radiance data provided in units of
Watts/(meter**2 steradian micron) and identified by the
mnemonic 'RADREV'. The RADREV data are considered to be
reversible because the calibration steps can be backed out to
return to the original, raw data numbers. A RADREV image can
be converted to unitless I-over-F by multiplying by the value
assigned to the DATA_TO_IOVERF_MULTIPLIER keyword in the PDS
label. Alternatively, a RADREV image can be converted from
radiance units to calibrated data numbers by multiplying by the
value assigned to the DATA_TO_DN_MULTIPLIER in the PDS label.
- Irreversibly cleaned radiance data provided in units of
Watts/(meter**2 steradian micron) and identified by the
mnemonic 'RAD'. The RAD data are considered to be
irreversible because the calibration steps, such as smoothing
over bad pixels, cannot easily be backed out to return to the
original, raw data numbers. A RAD image can be converted
to unitless I-over-F by multiplying by the value assigned to
the DATA_TO_IOVERF_MULTIPLIER keyword in the PDS label.
Alternatively, a RAD image can be converted from radiance units to
calibrated data numbers by multiplying by the value assigned to
the DATA_TO_DN_MULTIPLIER in the PDS label (though interpolated
pixels will not be real data). Please note that values in the
overclock rows and columns bordering the active CCD area are
set to 0 in the RAD product.
The calibration pipeline performed the following processes, in the
order listed, on the raw HRIV FITS data to produce the RADREV and
RAD products found in this data set (the process uses the image
mode and filter to select the appropriate set of calibration files):
- Decompression of compressed images
- Correction for bias
- Subtraction of a dark frame
- Removal of horizontal, instrumental striping
- Removal of electronic cross-talk
- Application of a normalized flat field
- Removal of CCD transfer smear
- Conversion of data numbers to units of radiance for an absolute,
radiometric calibration that is reversible (RADREV)
- Interpolation over bad and missing pixels identified in the
RADREV data to make a partially cleaned, irreversible, radiometric
calibration with units of radiance (RAD); Steps for despiking
(i.e., cosmic ray removal) and denoising the data which are part
of the RAD stream were not performed because the existing routines
are not robust
- Calculation of multiplicative factors to convert a RADREV or RAD
image to I-over-F
- The RAD stream has a potential step for deconvolving HRIV images
to correct for the out-of-focus condition for the HRI telescope
but this step was *not* performed
As part of the calibration process, the pipeline updated the
pixel-by-pixel image quality map, the first FITS extension, to identify:
- Pixels where the raw value was saturated,
- Pixels where the analog-to-digital converter was saturated,
- Pixels that were ultra-compressed and thus contain very little
information, and
- Pixels considered to be anomalous as indicated by bad pixel
maps (missing pixels were identified when the raw FITS files
were created).
The pipeline also created a FITS image extension to capture the
signal-to-noise ratio map and another extension to capture the values
used to remove horizontal striping. The calibration steps and files
applied to each raw image are listed in the PROCESSING_HISTORY_TEXT
keyword in the PDS data label.
Data
====
FITS Images and PDS Labels
--------------------------
Each calibrated HRIV image is stored as FITS. The primary data unit
contains the two-dimensional CCD image which is followed by two
image extensions that are two-dimensional pixel-by-pixel maps
providing additional information about the CCD image:
- The first extension uses one byte of eight, bit flags to
describe the quality of each pixel in the primary image.
The PDS data label defines the purpose of each bit.
- The second extension provides a signal-to-noise ratio for
each pixel in the primary image.
- The third extension contains the two columns of DN values that
were subtracted from every non-overclock column in the left
and right halves of the primary image array by the stripe
removal process.
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 and provides more information about the FITS primary
image and the extensions. Many values in a data 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_rr.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), nnn provides the image number
(IMAGE_NUMBER in the data labels) within the exposure ID, and
rr identifies the type of reduction:
RR for RADREV data (reversibly calibrated, radiance units)
R for RAD data (partially cleaned RADREV data, radiance units)
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 1000001, the
first FITS file name would be HV10090513_4000001_001_RR.FIT and the
last would be HV10090513_4000001_006_RR.FIT.
Image Compression
-----------------
All calibrated data products are uncompressed. If an associated raw
data product was compressed on-board the flyby spacecraft (and thus
received on the ground and archived as compressed) then the
calibration pipeline used one of four 8-bit lookup tables to
decompress the raw image. 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
----------
The calibrated RADREV and RAD image data have units of radiance,
W/(m**2 steradian micron).
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.
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