| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This dataset contains version 2.0 of raw calibration images acquired
by the Medium Resolution Visible CCD (MRI) from 04 October 2007 through
28 November 2010 during the EPOCh, 103P/Hartley 2 Encounter, and cruise
phases of the EPOXI mission. This dataset supersedes version 1.0 which
contained raw calibration only through July 2010.
The purpose of these data are to monitor the MRI CCD 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, Achernar, Beta Hyi, Canopus, HD 60753,
HD 79447, NGC 3114, NGC 7027, Vega, sky frames, stim lamp frames,
and dark frames. The Deep Impact calibration pipeline was the
foundation for EPOXI until improvements were implemented for the
Hartley 2 encounter as described in the Hartley 2 calibration summary
report located in the DOCUMENT directory. For a detailed discussion
of how the instruments were calibrated for EPOXI see Klaasen, et al.
(2011, in preparation) [KLAASENETAL2011]. The Deep Impact instrument
calibration is described by Klaasen, et al. (2008)[KLAASENETAL2006]
and Klaasen, et al. (2005) [KLAASENETAL2005].
A list of the calibration activities relevant to this dataset is
provided below and a description of each activity follows. The EPOXI
in-flight calibrations summary chart in the DOCUMENT directory provides
a quick-look at the activities.
------------------------------------------------------------------------
Phase and Exposure ID
Calibration Activity Obs Date/DOY Target Start Stop
---------------------------- -------------- -------- ------- -------
Cruise 1
Instrument Checkout 2007-10-04/277 Sky 1010200 1010215
EPOCh Photometry Test 2007-11-04/308 HD 80607 9400000 9400000
Lunar Calibration 2007-12-29/363 Moon 1000000 1000058
Standard Cruise Cal 2008-01-09/009 Beta Hyi 2000000 2000009
HD 79447 2000010 2000019
47 Tuc 2000020 2000020
Achernar 2000021 2000029
Canopus 2000030 2000042
HD 60753 2002000 2002007
NGC 3114 2002008 2002019
Stim Lamp 2002020 2002029
Dark 2002030 2002039
Vega 2010000 2010008
16 Cyg A 2010009 2010016
NGC 7207 2010017 2010017
Cruise 2
HRII Subframe Gain Cal/Moon 2009-01-26/026 Moon 4000000 4000062
HRII Lunar Radiometry&Flats 2009-06-02/153 Moon 1000000 1000076
HRII Lunar Rad&Antisat Fltr 2009-06-09/160 Moon 1000000 1000012
1000300 1000311
Checkout after HRI Turnoff 2009-09-30/273 Sky 1010200 1010215
HRII Rad Cal #1 (Beta Hyi) 2009-10-13/286 Beta Hyi ExpIDs 2000000
through through 2000005
2009-10-24/297 repeately used
HRII Lunar Flats/Rad Cal#1 2009-12-05/339 Moon 1000000 1000076
HRII Lunar Flats/Rad Cal#2 2009-12-12/346 Moon 1000000 1000076
HRII Lunar S.Pole Rad 2009-12-18/352 Moon 1000000 1000002
Standard Cruise Cal 2010-02-16/047 Beta Hyi 2000000 2000009
HD 79447 2000010 2000019
47 Tuc 2000020 2000020
Achernar 2000021 2000029
Canopus 2000030 2000042
Vega 2010000 2010008
16 Cyg A 2010009 2010016
NGC 7027 2010017 2010017
HD 60753 2002000 2002007
NGC 3114 2002008 2002019
Stim Lamp 2002020 2002031
Dark 2002032 2002039
HRII Rad Cal #2 (Beta Hyi) 2010-05-03/123 Beta Hyi ExpIDs 2000000
through through 2000005
2010-05-17/137 repeatedly used
MRI Dosido Fast Slew Test 2010-07-12/193 Dark ExpIDs 2100100
through 2100110
repeatedly used
Hartley 2 Encounter
Standard Cruise Cal 2010-09-28/271 Vega 2010000 2010008
(pre-encounter) to 16 Cyg A 2010009 2010016
2010-09-29/272 NGC 7027 2010017 2010017
Beta Hyi 2000000 2000009
HD 79447 2000010 2000019
47 Tuc 2000020 2000020
Achernar 2000021 2000029
Canopus 2000030 2000042
HD 60753 2002000 2002007
NGC 3114 2002008 2002019
Dark 2002020 2002029
Stim Lamp 2002030 2002039
Darks for E-34Days to 2010-10-01/274 Dark Various ExpIDs
E+12Days *to*2010-11-16/320
Standard Cruise Cal 2010-11-27/331 Vega 2010000 2010008
(post-encounter) to 16 Cyg A 2010009 2010016
2010-11-28/332 NGC 7027 2010017 2010017
Beta Hyi 2000000 2000009
HD 79447 2000010 2000019
47 Tuc 2000020 2000020
Achernar 2000021 2000029
Canopus 2000030 2000042
HD 60753 2002000 2002007
NGC 3114 2002008 2002019
Dark 2002020 2002029
Stim Lamp 2002030 2002039
------------------------------------------------------------------------
Instrument Checkout: On 4 October 2007, the three science instruments
were turned on for the first time in more than two years. Sky
frames acquired by the MRI CCD confirmed the mechanical components
such as the shutter and filter wheel were functioning. The
instrument exhibited nominal behavior of background levels.
EPOCh Photometry Test: On 4-9 November 2007, EPOCh photometry tests
were performed for the HRIV instrument to check pointing and
photometric stability. One MRI frame of the target, HD 80607, was
acquired.
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 (radiometry and scattered
light).
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. Good radiometry,
geometric, and linearity data were obtained.
HRII Subframe Gain Calibration: On 26 January 2009, an HRII subframe
gain calibration was conducted to observe differences in the IR
spectrometer signal response rates when observing an external
radiance source to differentiate between gain and offset effects
when using the various subframe modes. The test was performed by
scanning the spectrometer across the moon (cross slit) at multiple
speeds with various subframe modes while the HRI telescope barrel
was warm. MRI frames were acquired to provide context for the
IR scans.
HRII Lunar Radiometry and Flats: On 1-2 June 2009, the HRII
spectrometer acquired a series of north/south scans (cross slit)
of the moon for lunar radiometry and east/west scans along IR slit
for flats. These data were the best obtained to date for the
purpose of generating flat fields for the IR spectrometer. MRI
frames were acquired to provide context for the IR scans.
HRII Lunar Radiometry and Antisat Filter: On 9 June 2009, the HRII
spectrometer imaged the moon using north/south scans (cross slit)
to better characterize the effects of the anti-saturation filter
in the IR spectra. MRI frames were acquired to provide context
for the IR scans.
Checkout after HRI Turnoff: Before repeating the Earth South Pole
observation, a standard imaging checkout of the HRII, HRIV, and MRI
instruments was performed after HRI was powered up on 30 September
2009. The data included HRII spectra of the sky.
HRII Radiometric Cal #1 (Beta Hyi): From 13 October to 24 October
2009, the HRII spectrometer repeatedly scanned the star Beta Hyi to
improve the radiometric calibration for that instrument. MRI
frames were acquired to provide context for the IR scans.
HRII Lunar Flats/Radiometric Cal #1 and #2: On 05 and 12 December
2009 as the spacecraft approached Earth, the IR spectrometer made
north/south scans of the moon for radiometry and east/west scans
along the slit for lunar flats and a radiometric calibration.
MRI frames were acquired to provide context for the IR scans.
HRII Lunar South Pole Radiometry: On 18 December 2009, about 10
days before the distant flyby of Earth the IR spectrometer made
north/south scans of the lunar south pole for radiometric analysis.
MRI frames were acquired to provide context for the IR scans.
Standard Cruise Calibration: A full, standard cruise calibration
for HRII, HRIV, and MRI was completed on 16 February 2010. The
sequence was very similar to that used for the standard cruise
calibrations in 2008.
HRII Radiometric Cal #2 (Beta Hyi): From 03-17 May 2010, the HRII
spectrometer repeatedly scanned the star Beta Hyi to improve the
radiometric calibration for that instrument. MRI frames were
acquired to provide context for the IR scans.
MRI Dosido Fast Slew Test: On 12 July 2010, the MRI Dosido fast slew
sequence involved a test of the observing strategy planned from 8
days to 1 day before the Hartley 2 encounter that included periods
during which the spacecraft attitude was maneuvered once per hour
between the Earth downlink attitude and the comet viewing attitude.
The spacecraft was slewed at a high rate between these two
attitudes, and the Deep Space Network was required to lockup on the
downlink quickly every hour. MRI images of random space were taken
each hour at the comet viewing attitude as they will be during the
actual encounter sequence in early November 2010.
Pre-Encounter Standard Cruise Calibration: A full, standard cruise
calibration for HRII, HRIV, and MRI was performed on 28-29
September 2010. The sequence was very similar to that used
earlier in 2010.
Darks for E-34 Days to E+12 Days: The imaging sequences that were
executed from 01 October through 16 November 2010 for the encounter
of Hartley 2 included MRI dark frames for background and stripe
removal analyses.
Post-Encounter Standard Cruise Calibration: A full post-encounter
standard cruise calibration for HRII, HRIV, and MRI was performed
on 27-28 November 2010. The sequence was nearly identical to the
pre-encounter calibration performed in September.
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.
EPOXI_INFLIGHT_CAL_SUMMARY.PDF
- The EPOXI In-Flight Calibrations Summary provides an overview of
the instrument calibrations performed during the entire EPOXI
mission.
INSTRUMENTS_HAMPTON.PDF
- The Deep Impact instruments paper by Hampton, et al. (2005)
[HAMPTONETAL2005] provides very detailed descriptions of the
instruments.
MRI_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 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-E-MRI-2-EPOXI-EARTH-V1.0
DIF-E-MRI-3/4-EPOXI-EARTH-V1.0
- Raw and calibrated MRI Earth observations, used mainly for
context purposes.
DIF-M-MRI-2-EPOXI-MARS-V1.0
DIF-M-MRI-3/4-EPOXI-MARS-V1.0
- Raw and calibrated MRI Mars observations, used mainly for
context purposes.
DIF-C-MRI-2-EPOXI-HARTLEY2-V1.0
DIF-C-MRI-3/4-EPOXI-HARTLEY2-V1.0
- Raw and calibrated MRI comet Hartley 2 observations
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]
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-MRI-2-9P-CRUISE-V1.0
DIF-CAL-MRI-2-9P-ENCOUNTER-V1.0
- Deep Impact raw MRI calibrations datasets from 2005
DIF-CAL-HRII/HRIV/MRI-2-GROUND-TV4-V1.0
- Deep Impact raw MRI pre-launch calibrations from 2002 and 2003
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 MRI 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
MVyymmddhh_eeeeeee_nnn.LBL or FIT where 'MV' identifies the MRI
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 32
frames were commanded for a scan with an exposure ID of 1000000, the
first FITS file name would be MV07122918_1000000_001.FIT and the last
would be MV07122918_1000000_032.FIT.
Image Compression
-----------------
For some MRI calibration 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) increasing to the right in the display
window and the slowest-varying axis (lines)
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 MRI to the High Resolution Instrument Visible CCD
(HRIV) 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.
Target Name and Description
---------------------------
The TARGET_NAME keyword in the data labels is set to the intended
target, 'CALIBRATION', for each observation in this dataset. The
TARGET_DESC keyword provides the name of the specific calibration
target, such as 'DARK' or 'VEGA'.
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 For context; not band limited
2 C2 514 11.8 For C2 in coma
3 GREEN_CONT 526 5.6 For dust in coma
4 RED 750 100 For context
5 IR 950 100 For context; longpass
6 CLEAR6 600 >700 For context; not band limited
7 CN 387 6.2 For CN in coma
8 VIOLET_CONT 345 6.8 For dust in coma
9 OH 309 6.2 For OH in coma
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. NAIF used these kernels to produce 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 by the science teams to improve
the calibration of instrument.
Review
======
This dataset, Version 2.0, was peer reviewed and certified for
scientific use on 15 August 2011. It supersedes Version 1.0
which contained data only from October 2007 through July 2010.
Data Coverage and Quality
=========================
There are no unexpected gaps in this dataset. All calibration
observations received on the ground were processed and included in this
dataset.
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.
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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