| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains version 1.0 of raw calibration data
acquired by the High Resolution Visible CCD (HRIV) during the
EPOXI mission. The data for this version were collected from
04 October 2007 through 17 December 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 HRIV 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, Achernar, Beta Hyi, Canopus, HD 60753, HD 79447, NGC 3114,
NGC 7027, Vega, sky frames, stim lamp 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].
Additionally HD 80607 was imaged in early November 2007 as a
preliminary photometry check for EPOCh exoplanet transit observations.
A list of the calibration activities relevant to this data set is
provided here and a description of each activity follows.
Phase and Exposure ID
Calibration Activity Obs Date/DOY Target Start Stop
---------------------------- -------------- -------- ------- -------
Cruise 1
Instrument Checkout 2007-10-04/277 Sky 1010000 1010015
EPOCh Photometry Test 2007-11-04/308 HD 80607 9300000 9400000
2007-11-05/309 HD 80607 9300000 9300000
2007-11-08/312 HD 80607 9500000 9500005
2007-11-09/313 HD 80607 9500005 9500006
HRIV Scattered Light Cal 2007-12-17/351 Moon 1000000 1000056
Dark 1000056 1000065
Lunar Calibration 2007-12-29/363 Moon 1000003 1000026
Dark 1000027 1000029
Standard Cruise Cal 2008-01-09/009 Beta Hyi 2000000 2000008
HD 79447 2000009 2000017
Achernar 2000018 2000025
Canopus 2000026 2001269
HD 60753 2002000 2002008
NGC 3114 2002009 2002020
Vega 2010000 2010012
16 Cyg A 2010013 2010021
NGC 7207 2010025 2010029
Dark 2010030 2010039
Stim Lamp 2010040 2010049
EPOCh
Darks/Stims for Transit Obs 2008-01-22/022 Dark 9600000 9600001
*to*2008-08-31/244 Stim Lamp 9600002 9600003
Darks for Earth Obs #1 2008-03-19/079 Dark 1001235 1001241
Darks for Earth Obs #4 2008-05-29/150 Dark 1001235 1001241
Darks for Earth Obs #5 2008-06-05/157 Dark 1001235 1001241
Standard Cruise Cal 2008-06-23/175 Vega 2010003 2010015
16 Cyg A 2010016 2010024
NGC 7207 2010025 2010029
Dark 2010030 2010039
Stim Lamp 2010040 2010049
2008-06-24/176 Beta Hyi 2000000 2000008
HD 79447 2000009 2000017
Achernar 2000018 2000025
Canopus 2000026 2000038
Canopus 2001000 2001269
HD 60753 2002000 2002008
NGC 3114 2002009 2002018
2008-06-25/177 NGC 3114 2002019 2002020
Cruise 2
HRIV PSF Calibration 2008-12-17/352 Canopus 7100000 7100008
Achernar 7100009 7100017
Dark 7100018 7100018
Stim Lamp 7100019 7100020
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 HRIV 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. During these tests, the HRIV instrument observed a
bright (V=9) visual binary star (HD 80607) for 12 continuous hours
to check pointing and photometric stability. The observations were
taken using the 256-by-256 sub-array mode of the HRIV CCD. The
spacecraft successfully captured the star images and held them on
the sub-array for the full duration of the test. However the images
were unexpectedly offset by 29 microradian (12.2 arcsec). This was
due to stellar aberration, which was not included for stellar
observations during the Deep Impact mission. After correcting for
aberration, the spacecraft pointing was within specifications.
HRIV Scattered Light Calibration: On 17 December 2007, a
calibration for scattered light using Earth's moon was performed
for the HRIV instrument. Many of these images were obtained with
the moon outside but near the field of view of the HRIV CCD to
allow analysis of the amount of light that is scattered into the
field of view from bright objects just outside or within the field
of view.
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.
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.
EPOCh Darks/Stims for Transit Obs: Observations of EPOCh transiting
extrasolar planets were bracketed by sets of dark and internal
stimulator lamp frames to aid photometric analysis. These frames,
acquired from 22 January through 31 August 2008, are sub-frame
images (256x256 or 128x128 pixels) with exposure times of 50 or 100
milliseconds. Unique exposure IDs were assigned for these
EPOCh-specific calibrations: 9600000 and 9600001 for the darks and
9600002 and 9600003 for the stim lamp frames.
EPOCh Darks for Earth Obs: At the end of each Earth observation
period, a set of HRIV dark frames was acquired for calibration
purposes and is included in this data set.
Standard Cruise Calibration: A second standard cruise calibration
was performed on 23-25 June 2008 for the HRIV and HRII 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.
HRIV PSF Calibration: On 17 December 2008, additional data were
acquired for improving point spread functions (PSF) for the HRIV
CCD. Analysis of early EPOXI calibration data and EPOCh stellar
observations indicated the PSFs had changed since mid-2005 when the
functions were last generated for Deep Impact. The project plans
to rerun this sequence in 2010 for the Hartley 2 flyby.
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 version.
INSTRUMENTS_HAMPTON.PDF
- The Deep Impact instruments paper by Hampton, et al. (2005)
[HAMPTONETAL2005] provides very detailed descriptions of the
instruments.
HRIV_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-HRIV-2-EPOXI-EARTH-V1.0
DIF-E-HRIV-3/4-EPOXI-EARTH-V1.0
- Raw and calibrated HRIV Earth observations
DIF-C-HRIV-2-EPOXI-HARTLEY2-V1.0
DIF-C-HRIV-3/4-EPOXI-HARTLEY2-V1.0
- Raw and calibrated HRIV 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-HRIV-2-9P-CRUISE-V1.0
DIF-CAL-HRIV-2-9P-ENCOUNTER-V1.0
- Deep Impact raw HRIV calibrations data sets from 2005
DIF-CAL-HRII/HRIV-2-GROUND-TV2-V1.0
DIF-CAL-HRII/HRIV/MRI-2-GROUND-TV4-V1.0
- Deep Impact raw HRIV 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 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 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 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
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 32
frames were commanded for a scan with an exposure ID of 1000000, the
first FITS file name would be HV07122918_1000000_001.FIT and the last
would be HV07122918_1000000_032.FIT.
Image Compression
-----------------
For some HRIV 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. For more information about this topic,
see the image compression section of the Deep Impact instrument
calibration document.
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
Deep Impact instrument calibration document. Also the EPOXI SIS
has a brief discussion of this topic.
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 relative boresight alignments section 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.
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
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 list of the characteristics of the HRIV filters is provided below.
For more information about the filters, see the Deep Impact
instruments document or the Deep Impact instrument calibration
document. Also the EPOXI SIS has a brief discussion of this topic.
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
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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