| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains raw science calibration images acquired by the
Deep Impact Medium Resolution Instrument Visible CCD (MRI) during
the cruise phase of the mission to comet 9P/Tempel 1. The data set
does not contain images of the comet.
The science calibrations images are described in the 'Deep Impact
In-Flight Calibration Summary' document and are also discussed in the
'Deep Impact: Anticipated Flight Data' paper by Klaasen, et al. (2005)
[KLAASENETAL2005]. Calibration targets included the Earth, Moon,
Jupiter, 16 Cyg A, Achernar, Beta Hyi, Canopus, Vega, HD 60753, HD
79447, IC 2391, M11, NGC 3114, NGC 3532, an internal calibration
(stimulator) lamp, sky, and dark frames. For a detailed discussion of
the instrument was calibrated, see 'Deep Impact Instrument
Calibration' by Klaasen, et al. (2006) [KLAASENETAL2006].
A list of the images for science calibrations in the data set is
provided here:
Mid-Obs Exposure IDs
Date DOY Minimum Maximum Mission Activity
---------- --- ------- ------- --------------------------
2005-01-14 014 1000000 1000005 Checkout
2005-01-15 015 1000006 1010215 Checkout
2005-01-16 016 1100000 1100051 Moon/Earth Science Cal
2005-01-25 025 1200000 1200009 MRI Stray Light/MRI Turn-off Anomaly
2005-01-26 026 1200000 1200000 MRI Stray Light/MRI Turn-off Anomaly
2005-01-28 028 1200000 1200022 MRI Stray Light Test
2005-01-29 029 1200023 1200092 MRI Stray Light Test
2005-01-30 030 1500000 1500016 Lunar Science Cal
2005-02-04 035 1500000 1500016 Lunar Science Cal rerun
2005-02-06 037 1200000 1300015 Flyby Autonav Test
2005-02-15 046 1700000 1700000 MRI Focus Test
2005-02-21 052 1700000 1700000 MRI Focus Test
2005-03-03 062 2100040 2100048 MRI Stray Light/Geometry
2005-03-24 083 9000878 9001043 Encounter Validation Test
2005-04-05 095 2000000 2010025 April Science Cal
2005-04-06 096 2020000 2030026 April Science Cal
2005-04-07 097 2040000 2040047 April Science Cal
2005-04-08 098 2050000 2070020 April Science Cal
2005-04-27 117 1800000 1800009 MRI Stray Light Test
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]
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
AIDC_FLIGHT_HRIV_MRI_ITS.* : Description of the data set and
definitions of label keywords
Related Data Sets
-----------------
The following PDS data sets are related to this one:
DIF-CAL-MRI-2-9P-ENCOUNTER-V1.0 : Raw MRI encounter data
DIF-C-MRI-3/4-9P-ENCOUNTER-V1.0 : Reduced MRI encounter data
DIF-CAL-HRII/HRIV/MRI-2-GROUND-TV4-V1.0 : MRI pre-flight calib data
DI-C-SPICE-6-V1.0 : SPICE kernels
Processing
==========
The uncompressed and compressed FITS images in this data set were
created by the Deep Impact Science Data Center (SDC) at Cornell
University and were assembled from raw telemetry packets sent down by
the flyby spacecraft. Information from the embedded spacecraft header
(the first 100 bytes of an uncompressed or 50 bytes of a compressed
image) 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 image quality
map is described in the calibration pipeline section of the 'Deep
Impact Instrument Calibration' paper by Klaasen, et al. (2006)
[KLAASENETAL2006]. The SDC did not apply any type of correction or
decompression algorithm to the raw data.
Applied Coherent Technology Corporation in Herndon, VA, produced the
PDS data labels by extracting parameters from the FITS headers.
Data
====
CCD Images
----------
The two-dimensional, visible CCD images in this data set are in
FITS format. The primary data array contains the CCD image and
is followed by an image extension that contains a pixel-by-pixel
quality map. Each FITS file is accompanied by a detached PDS label.
Compression
-----------
This data set contains compressed and uncompressed raw FITS images,
that is, data as they were received on the ground. Data compression
was performed on board the spacecraft using a set of four lossy
lookup tables. A compressed FITS image consisted of 14-bit values
compressed and stored as a one-byte pixel. An uncompressed FITS
image consisted of 14-bit pixels stored as two bytes. The
COMPRESSED_IMAGE_VALUE in the data label indicates if an raw image
is compressed or uncompressed. The COMPRESSOR_ID identifies the
lookup table that was used to compress an image.
The calibration pipeline decompressed raw images. For information
about data compression, refer to 'An Overview of the Instrument
Suite for the Deep Impact Mission' by Hampton, et al. (2005)
[HAMPTONETAL2005] or the instrument calibration paper by Klaasen,
et al. (2006) [KLAASENETAL2006].
Target Name and Description
---------------------------
The TARGET_NAME keyword in the data labels was set to the intended
target, 'Calibration'. The TARGET_DESC keyword provides the name
of the specific calibration target, such as 'Dark'.
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 image labels:
SAMPLE_DISPLAY_DIRECTION = 'RIGHT'
LINE_DISPLAY_DIRECTION = 'UP'
This topic is discussed in detail in the 'Quadrant Nomenclature'
section of the 'Deep Impact Instrument Calibration' document.
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.
File Naming Convention
----------------------
The naming convention for the data labels and FITS files is
MVcccccccccc_eeeeeee_nnn.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 corresponding 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
MV0173709840_9000022_001.FIT and MV0173709840_9000022_002.FIT.
Parameters
==========
Data Units
----------
Raw image data are in units of raw data numbers.
Imaging Modes and Filters
------------------------
For descriptions of the imaging modes and filters, please see
the Deep Impact instrument paper by Hampton, et al. (2005)
[HAMPTONETAL2005].
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.
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 estimated impact time at the flyby spacecraft of UTC
05:44:35.821 on 4 Jul 2005.
Geometry-Related Keywords
-------------------------
The SDC attempted to calculate geometric parameters relating to
the target only when it was within several fields of view of the
instrument boresight. When these parameters could not be
calculated, the corresponding keywords in the PDS data labels were
set to a value of unknown (UNK). Also, geometry-related keywords
for calibration targets such as Canopus were set to UNK.
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. The Deep Impact
project generated self-consistent SPICE kernels, outside of NAIF, to
help account for the discrepancy. The November 2005 version of
these kernels was used to calculate the image times and geometric
information in PDS data labels. After further analysis of the
timing problem in early 2006, improved self-consistent SPICE kernels
were generated by the Deep Impact project. These kernels are
included in the DI SPICE data set. For more information about
this discrepancy, please see the spacecraft clock correlation
document included on the Deep Impact document volume.
Ancillary Data
==============
Geometric parameters included in the data labels were computed using
the November 2005 version of the SPICE data. These were the best
available data at the time of image creation. Since image creation,
some SPICE data have been improved, and these are 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. Geometric parameters were based on
the best available SPICE data when the FITS image was created.
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.
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