| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains raw spectra for science calibrations acquired
by the Deep Impact High Resolution Instrument Infrared Spectrometer
(HRII) during the cruise phase of the mission to comet 9P/Tempel 1.
The data set does not contain spectra of the comet.
The raw spectra for science calibrations 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, Beta Hyi, Canopus, Sirius, Vega, HD 60753, IC2391, NGC 3114, NGC
6543, sky, and dark frames. For a detailed discussion of how the
instrument was calibrated, see 'Deep Impact Instrument Calibration' by
Klaasen, et al. (2006) [KLAASENETAL2006].
A list of the raw spectra for science calibrations in the data set
is provided here:
Mid-Obs Exposure IDs
Date DOY Minimum Maximum Mission Activity
---------- --- ------- ------- --------------------------
2005-01-15 014 1010100 1010107 Instrument Checkout
2005-01-16 016 1100000 1100049 Moon/Earth Science Cal
2005-01-30 030 1500000 1500019 Lunar Science Cal
2005-02-04 035 1500000 1500019 Lunar Science Cal Rerun
2005-03-24 083 9000056 9000064 Encounter Validation Test
2005-04-05 095 2000000 2010001 April Science Cal
2005-04-06 096 2020000 2030001 April Science Cal
2005-04-07 097 2040000 2040003 April Science Cal
2005-04-08 098 2060000 2070001 April Science Cal
2005-04-27 117 1800000 1800005 IR 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_HRII.* : 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-HRII-2-9P-ENCOUNTER-V1.0 : Raw HRII encounter data
DIF-C-HRII-3/4-9P-ENCOUNTER-V1.0 : Reduced HRII encounter data
DIF-CAL-HRII-2-GROUND-TV1-V1.0 : HRII pre-flight calib data
DIF-CAL-HRII/HRIV-2-GROUND-TV2-V1.0 : HRII pre-flight calib data
DIF-CAL-HRII/HRIV/MRI-2-GROUND-TV4-V1.0 : HRII 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 was 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
====
Spectral Images
---------------
The two-dimensional, infrared spectral images in this data set are
in FITS format. The primary data array contains the spectral
image, with the fastest varying axis corresponding to increasing
wavelengths and the slowest varying axis providing the spatial
dimension. It 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
HIcccccccccc_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
HI0173709840_9000022_001.FIT and HI0173709840_9000022_002.FIT.
For the HRII instrument, multiple images for one exposure ID
indicate a scan of the target.
Parameters
==========
Data Units
----------
Raw image data are in units of raw data numbers.
Imaging Modes
-------------
For a description of the imaging modes, please see the Deep Impact
instrument paper by Hampton, et al. (2005) [HAMPTONETAL2005].
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 have been 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 newer kernels 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 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.
|
| CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview
=========================
As noted above, the 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. For more information about this discrepancy, please
see the spacecraft clock correlation document included on the Deep
Impact document volume.
The FITS files in this data set were reviewed internally by the Deep
Impact project and were used extensively by the science team to
calibrate the instruments.
Review
======
This data set passed a PDS peer review that took place on April 5,
2006. Reviewers stated these data should be archived pending
resolution of the liens produced during the review.
Data Coverage and Quality
=========================
All expected data were received on the ground and are included in
this data set.
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 notes about image quality map in the
PDS data label or to the 'Deep Impact Instrument Calibration' paper.
Limitations
===========
HRI Telescope Focus
-------------------
Early images of stars using the HRI visible CCD indicated the HRI
telescope was out of focus. However, this focus problem did not
affect the HRII instrument. For more details, please see the
instrument calibration paper by Klaasen et al. (2006)
[KLAASENETAL2006].
Displaying Images
-----------------
Flight software overwrote the first 50 uncompressed (or 100
compressed) pixels of first quadrant read out from the instrument
with an image header. These original header pixels were included in
the raw FITS images. Since the values in these pixels vary
dramatically, it recommended that the values of the MINIMUM and
MAXIMUM keywords in the PDS 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 reference rows
and columns located around the edge of the spectral image. The
location of the header pixels in a displayed FITS image depends on
the readout order of the instrument, as discussed in the quadrant
nomenclature section of the 'Deep Impact Instrument Calibration'
paper.
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