| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains version 2.0 of calibrated images of comet
9P/Tempel 1 acquired by the Deep Impact High Resolution Instrument
Visible CCD (HRIV) during the encounter phase of the mission.
Version 2.0 includes uncleaned radiance, cleaned radiance, and
I-over-F data with improved geometry. The data were collected from
1 May through 4 July 2005.
A summary of the comet observations in this data set is provided here:
Mid-Obs Exposure IDs
Date DOY Minimum Maximum Mission Activity
---------- --- ------- ------- --------------------------
2005-05-01 121 5000100 5000108 Daily Comet Imaging
2005-05-07 127 5000700 5000716 Daily Comet Imaging
2005-05-08 128 5000800 5000835 Daily Comet Imaging
2005-05-15 135 5001500 5001543 Daily Comet Imaging
2005-05-16 136 5001600 5001653 Daily Comet Imaging
2005-05-17 137 5001700 5001753 Daily Comet Imaging
2005-05-18 138 5001800 5001853 Daily Comet Imaging
2005-05-19 139 5001900 5001953 Daily Comet Imaging
2005-05-25 145 5002500 5002553 Daily Comet Imaging
2005-05-26 146 5002600 5002644 Daily Comet Imaging
2005-05-27 147 5002700 5002743 Daily Comet Imaging
2005-05-28 148 5002800 5002833 Daily Comet Imaging
2005-05-29 149 5002900 5002952 Daily Comet Imaging
2005-05-30 150 5003000 5003052 Daily Comet Imaging
2005-05-31 151 5003100 5003116 Daily Comet Imaging
2005-06-03 154 6000300 6000353 Daily Comet Imaging
2005-06-04 155 6000400 6000453 Daily Comet Imaging
2005-06-05 156 6000500 6000517 Daily Comet Imaging
2005-06-10 161 6001000 6001026 Daily Comet Imaging
2005-06-11 162 6001100 6001135 Daily Comet Imaging
2005-06-12 163 6001200 6001217 Daily Comet Imaging
2005-06-13 164 6001300 6001344 Daily Comet Imaging
2005-06-14 165 6001400 6001435 Daily Comet Imaging
2005-06-15 166 6001500 6001553 Daily Comet Imaging
2005-06-16 167 6001600 6001626 Daily Comet Imaging
2005-06-17 168 6001700 6001744 Daily Comet Imaging
2005-06-18 169 6001800 6001835 Daily Comet Imaging
2005-06-19 170 6001900 6001953 Daily Comet Imaging
2005-06-20 171 6002000 6002053 Daily Comet Imaging
2005-06-21 172 6002100 6002153 Daily Comet Imaging
2005-06-22 173 6002200 6002253 Daily Comet Imaging
2005-06-23 174 6002300 6002353 Daily Comet Imaging
2005-06-24 175 6002400 6002453 Daily Comet Imaging
2005-06-25 176 6002500 6002544 Daily Comet Imaging
2005-06-26 177 6002600 6002635 Daily Comet Imaging
2005-06-27 178 8000000 8000053 Daily Comet Imaging
2005-06-28 179 8000045 8100044 Daily Comet Imaging
2005-06-29 180 8100045 8300008 Daily Comet Imaging
2005-06-30 181 8400000 8400053 Daily Comet Imaging
2005-07-01 182 8400054 8500089 Daily Comet Imaging
2005-07-02 183 8500090 8500107 Daily Comet Imaging
8600000 8600062 Continuous Comet Imaging
2005-07-03 184 9000000 9000320 Continuous Comet Imaging
2005-07-04 185 9000322 9000908 Continuous Comet Imaging
9000909 9001051 Impact Imaging
9010000 9070016 Lookback Imaging
The 9P/Tempel 1 data are described in 'Deep Impact: The Anticipated
Flight Data' by Klaasen, et al. (2005) [KLAASENTAL2005]. For more
details about the images taken around impact, refer to the HRIV
encounter data summary document which provides a log of the exposures
taken from 28 hours before impact through lookback. Both of these
documents are included on the Deep Impact Documentation volume.
Essential Reading
-----------------
The following documents, located on the Deep Impact Documentation
volume, DIDOC_0001, are essential for the understanding and
interpretation of this data set:
ANTICIPATED_FLIGHT_DATA.* : Anticipated flight data by Klaasen,
et al. (2005) [KLAASENTAL2005]
HRIV_REDUCED_ENC_INDEX.* : Science-related index table for
this data set
HRIV_ENCOUNTER_DATA_SUMMARY.* : Image log from 28 hours before
impact through lookback
INFLIGHT_CALIBRATION_SUMMARY.* : Summary of in-flight calibrations
CALIBRATION_DOC.* : Instrument calibration by Klaasen,
et al. (2006) [KLAASENETAL2006]
INSTRUMENTS_HAMPTON.* : Instrument paper by Hampton, et al.
(2005) [HAMPTONETAL2005]
MISSION_OVERVIEW_AHEARN.* : Mission overview by A'Hearn, et al.
(2005) [AHEARNETAL2005B]
SCLK_CORRELATION.* : Discussion of the discrepancy
between the spacecraft clocks and
UTC
AICD_FLIGHT_HRIV_MRI_ITS.* : Description of the data set and
definitions of label keywords
Initial results from the encounter and impact were presented in
'Deep Impact: Excavating Comet Tempel 1' by by A'Hearn, et al.
(2005) [AHEARNETAL2005A].
Related Data Sets
-----------------
The following PDS data sets are related to this one:
DIF-CAL-HRIV-2-9P-CRUISE-V1.0 : Raw HRIV cruise calibrations
DIF-C-HRIV-3/4-9P-ENCOUNTER-V2.0 : Raw HRIV encounter data
DIF-C-HRII/HRIV/MRI-6-TEMPS-V1.0 : Instrument temperature data
DIF-CAL-HRII/HRIV-2-GROUND-TV2-V1.0 : HRIV pre-flight calib data
DIF-CAL-HRII/HRIV/MRI-2-GROUND-TV4-V1.0 : HRIV pre-flight calib data
DI-C-SPICE-6-V1.0 : SPICE kernels
Processing
==========
The calibrated two-dimensional FITS images in this data set were
generated by the Deep Impact calibration pipeline, maintained by the
project's Science Data Center (SDC) at Cornell University. For
these data (version 2.0), geometric parameters were computed using
the final kernels found in the PDS SPICE archive for Deep Impact.
The pipeline performed the following reduction steps to produce the
images in this data set:
- Decompression of compressed images
- Subtraction of a dark frame
- 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 ('RADREV')
- Interpolation over bad and missing pixels for partially cleaned,
radiometric calibration ('RAD')
- Conversion of cleaned radiance images ('RAD') to I-over-F
images ('IF')
The uncleaned radiance data, designated by the mnemonic 'RADREV',
were provided in units of radiance as Watts/(meter**2 steradian
micron). These data were considered reversible because the
calibration steps could be removed to get back to the original, raw
data numbers. Only the RADREV data were included in version 1.0 of
this data set.
The irreversibly cleaned radiance data, designated by the mnemonic
'RAD', were provided in units of radiance, Watts/(meter**2 steradian
micron). Cosmic rays were not removed because the existing
calibration routine was not robust. Also, the RAD images
were not deconvolved (which corrects for the out-of-focus problem
with the HRIV telescope).
Finally, each cleaned radiance (RAD) image was divided by the solar
spectrum at the target body's distance from the sun then multiplied
by pi to produce a unitless I/F (I-over-F) image. These data were
designated by the mnemonic 'IF'. Cosmic rays were not removed
from these data, and the images were not deconvolved.
During the calibration process, the pipeline updated the
pixel-by-pixel image quality map, the first FITS extension,
to identify the following types of pixels:
- 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
- Pixels considered bad 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 for a signal-to-noise
ratio map. The calibration steps and files used to reduce each raw
image are listed in the PROCESSING_HISTORY_TEXT keyword in the PDS
data label for that image. For a detailed discussion of the
calibration pipeline and the resulting data, see the instrument
calibration document by Klaasen, et al. (2006) [KLAASENETAL2006]
included on the Deep Impact Documentation volume.
Applied Coherent Technology Corporation in Herndon, VA, produced the
PDS data labels by extracting parameters from the FITS headers.
Data
====
File Naming Convention
----------------------
The naming convention for the data labels and FITS files is
HVcccccccccc_eeeeeee_nnn_rr.LBL or FIT where cccccccccc is the
spacecraft clock count at the mid-point of the observation, eeeeeee
is the exposure ID (OBSERVATION_ID in data labels). Up to 999
individual images could be commanded for one exposure ID.
Therefore, nnn in the file name provides the sequentially increasing
image number within an exposure ID and corresponds to IMAGE_NUMBER
in the data labels. For example, if two images were commanded for
exposure ID 9000022, the two FITS files names would be
HV0173709840_9000022_001_RR.FIT and HV0173709840_9000022_002_RR.FIT.
Finally, rr identifies the type of reduction:
RR for RADREV data (radiance units, reversible)
R for RAD data (radiance units, partially cleaned)
I for IF data (unitless I-over-F, partially cleaned)
CCD Images
----------
The two-dimensional, CCD images in this data set are in FITS format.
The primary data array contains the image, followed by two image
extensions that are pixel-by-pixel maps which provide additional
information about the primary 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.
Each image FITS file is accompanied by a detached PDS label. For
more information about the FITS primary image and extensions, refer
to the instrument calibration document included on the Deep Impact
Documentation volume.
Imaging Modes
-------------
A summary of the imaging modes is provided below. All image modes
are unbinned. For a thorough description of the modes, please see
the Deep Impact instrument paper by Hampton, et al. (2005)
[HAMPTONETAL2005] included on the Deep Impact Documentation
volume.
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
Most image modes had 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.
Filters
-------
A list of the characteristics of the HRIV filters is provided
below. For more information about the filters, refer to the Deep
Impact instrument paper by Hampton, et al. (2005)
[HAMPTONETAL2005] and the instrument calibration document included
on the Deep Impact Documentation volume.
Filter Center Width
Name (nm) (nm) Comments
---------- ----- ----- -------------------------------
CLEAR1 650 >700 Uncoated and not band limited
BLUE 450 100
GREEN 550 100
VIOLET 350 100 Shortpass coating
IR 950 100 Longpass
CLEAR6 650 >700 Uncoated and not band limited
RED 750 100
NIR 850 100
ORANGE 650 100
Compression
-----------
All data files in this data set were uncompressed. If the
associated raw data file 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 lossy
lookup tables to decompress raw image. For information about data
compression, see the Deep Impact instruments document by Hampton,
et al. (2005) [HAMPTONETAL2005] or the instrument calibration
paper by Klaasen, et al. (2006) [KLAASENETAL2006] included on the
Deep Impact Documentation volume.
The calibration pipeline used one of four lossy lookup tables to
decompress raw images that were compressed onboard the spacecraft.
For information about data compression, see the Deep Impact
instruments document by Hampton, et al. (2005) [HAMPTONETAL2005] or
the instrument calibration paper by Klaasen, et al. (2006)
[KLAASENETAL2006].
True-Sky 'As Seen By Observer' Display
----------------------------------------
A true-sky 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 increasing to the top. This convention is also
defined in the data labels:
SAMPLE_DISPLAY_DIRECTION = 'RIGHT'
LINE_DISPLAY_DIRECTION = 'UP'
The direction to Celestial North and Ecliptic North, measured
clockwise from the top of the displayed image, is provided in PDS
labels by CELESTIAL_NORTH_CLOCK_ANGLE and
SOLAR_NORTH_POLE_CLOCK_ANGLE, both of which assume the correct
display defined by SAMPLE_DISPLAY_DIRECTION and
LINE_DISPLAY_DIRECTION.
Using this convention for Tempel 1 approach images, ecliptic East is
toward the top, ecliptic North is toward the right, and the Sun is
down. After impact, the Flyby spacecraft came out of shield mode
and turned around to lookback at the comet. For lookback images,
ecliptic East is toward the top, ecliptic North is toward the left,
and the Sun is down.
For a comparison of the orientation of HRIV flight images with those
from ground-based calibrations as well as those from the Medium
Resolution Instrument CCD (MRI) and the Impactor Targeting Sensor
CCD (ITS), see the quadrant nomenclature section of the instrument
calibration document.
It is important to note that, in published results about the
encounter, the project elected to rotate HRIV images such that
ecliptic East is to the left, ecliptic North is up, and the Sun is
to the right for approach images. This is equivalent to rotating an
image counter-clockwise by 90 degrees with respect to the convention
provided above. Published lookback images were rotated clockwise by
90 degrees with with respect to the convention provided above such
that ecliptic East to the right, ecliptic North up, and the Sun to
the left.
Parameters
==========
Data Units
----------
Reduced RADREV and RAD data are in units of radiance,
W/(m**2 steradian micron). I/F data are unitless.
Time-Related Keywords
---------------------
All time-related keywords in the data labels, except
EARTH_RECEIVED_TIME, are based on the clock on board the flyby
spacecraft. EARTH_RECEIVED_TIME provides the UTC when an
Earth-based observer should be able to see an event recorded by
the instrument.
The TIME_FROM_IMPACT_VALUE keyword in the data labels was based
on the best estimate of the time of impact based on the clock
onboard the flyby spacecraft was UTC 05:44:34.265 on 4 Jul 2005.
The analysis that lead to this estimate is discussed in the
spacecraft clock correlation document included on the Deep Impact
documentation volume.
Geometry-Related Keywords
-------------------------
The SOLAR_NORTH_POLE_CLOCK_ANGLE in the data labels specified the
the direction of ecliptic north as projected onto the image plane.
It is measured from the 'upward' direction, clockwise to the
direction toward ecliptic north when the image is displayed as
defined by the SAMPLE_DISPLAY_DIRECTION and LINE_DISPLAY_DIRECTION
keywords.
The SDC pipeline was not able to automatically determine the
proper geometric information for the target of choice in many
cases. When these parameters could not be computed, the
corresponding keywords in the PDS data labels were set to a
value of unknown (UNK). Geometry-related keywords for most
calibration targets were set to UNK.
Geometric parameters provided in the data labels were computed at
the epoch specified by MID_IMAGE_TIME, except for the target-to-sun
and earth-observer-to-target parameters. Target-to-sun values were
calculated for the time when the light left the sun while
earth-observer-to-target were calculated for the time when the light
left the target.
Geometry-related parameters in the PDS data labels are uncertain at
a level of a few seconds because of a known 2-second discrepancy
between the clocks on board the flyby and impactor spacecraft and
between in-situ data and ground-based observations. After a
detailed analysis of the timing problem in early 2006, improved
self-consistent SPICE kernels were generated by the Deep Impact
project to correlate the spacecraft clocks; there is still a
1-2 second uncertainty between the in-situ data and the ground-
based observations and an uncertainty of about one half of a
second between the clocks on the flyby and impactor spacecraft.
These improved kernels were included in the DI SPICE data set
and were used to calculate the geometric parameters in the PDS
data labels. For more information about this discrepancy, please
see the spacecraft clock correlation report provided on the DI
documentation volume, DIDOC_0001.
The SPICE kernels used to calculated the geometric parameters are
provided by the SPICE_FILE_NAME keyword in the PDS data labels. The
kernels were listed in the order they were loaded into memory for
processing.
Ancillary Data
==============
Geometric parameters included in the data labels were computed using
the final version of the kernel files archived in the Deep Impact
SPICE data set.
Coordinate System
=================
Earth Mean Equator and Vernal Equinox of J2000 (EME J2000) was the
inertial reference system used to specify observational geometry
parameters in the data labels.
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