Data Set Information
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| DATA_SET_NAME |
DEEP IMPACT 9P/TEMPEL ENCOUNTER - REDUCED HRII SPECTRA V2.0
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| DATA_SET_ID |
DIF-C-HRII-3/4-9P-ENCOUNTER-V2.0
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| NSSDC_DATA_SET_ID |
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| DATA_SET_TERSE_DESCRIPTION |
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| DATA_SET_DESCRIPTION |
Data Set Overview : This data set contains version 2.0 of calibrated spectral images of comet 9P/Tempel 1 acquired by the Deep Impact High Resolution Instrument Infrared Spectrometer (HRII) during the encounter phase of the mission. Version 2.0 includes uncleaned and cleaned radiance data with improved calibration and geometry. The data were collected from 20 June through 6 July 2005. Spectra taken before June 20, 2005, are not included in this data set because the spectrometer was not pointing at the target. A summary of the comet observations in this data set is provided here: Mid-Obs Exposure IDs Date DOY Minimum Maximum Mission Activity ---------- --- ------- ------- -------------------------- 2005-06-20 171 6002005 6002005 Daily comet imaging 2005-06-21 172 6002100 6002105 Daily comet imaging 2005-06-22 173 6002200 6002205 Daily comet imaging 2005-06-23 174 6002300 6002305 Daily comet imaging 2005-06-24 175 6002400 6002405 Daily comet imaging 2005-06-25 176 6002500 6002504 Daily comet imaging 2005-06-26 177 6002600 6002603 Daily comet imaging 2005-06-27 178 8000000 8000004 Continuous comet imaging 2005-06-28 179 8000005 8100004 Continuous comet imaging 2005-06-29 180 8100005 8300000 Continuous comet imaging 2005-06-30 181 8400000 8400005 Continuous comet imaging 2005-07-01 182 8400006 8500009 Continuous comet imaging 2005-07-02 183 8500009 8800003 Continuous comet imaging 2005-07-03 184 9000000 9000021 Continuous comet imaging 2005-07-04 185 9000022 9000029 Continuous comet imaging 9000030 9000039 Pre-impact scans 9000040 9000068 Impact imaging 9010000 9070002 Lookback imaging 2005-07-05 186 9080000 9110002 Lookback imaging 2005-07-06 187 9120000 9150002 Lookback imaging The 9P/Tempel 1 spectra were described in 'Deep Impact: The Anticipated Flight Data' by Klaasen, et al. (2005) [KLAASENTAL2005]. For more details about the spectra taken around impact, refer 1) to the HRII encounter data summary document which provides a log of the exposures taken from 28 hours before impact through lookback and 2) the HRII encounter pointing summary document which describes the pointing and scan direction for exposures taken at encounter. These documents are included on the Deep Impact Documentation volume. Essential Reading ----------------- The following documents, located on the Deep Impact Documentation volume, DIDOC_1000, are essential for the understanding and interpretation of this data set: ANTICIPATED_FLIGHT_DATA.* : Anticipated flight data by Klaasen, et al. (2005) [KLAASENTAL2005] HRII_REDUCED_ENC_INDEX.* : Science-related index table for this data set HRII_ENCOUNTER_DATA_SUMMARY.* : Image log from 28 hours before impact through lookback HRII_ENCOUNTER_POINTING_SUMM.* : Pointing and scan directions for encounter data from June 20 through July 6 HRII_HRIV_CONTEXT_MAPS/* : HRII/HRIV context maps show where the IR slit was located on the closest HRIV CCD frame HRII_CALIBRATION_LIMITATIONS.* : Discusses known deficiencies in the IR calibration process that reduced the spectral images 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_HRII.* : 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-HRII-2-9P-CRUISE-V1.0 : Raw HRII cruise calibrations DIF-C-HRII-2-9P-ENCOUNTER-V1.0 : Raw HRII encounter data DIF-C-HRII/HRIV/MRI-6-TEMPS-V1.0 : Instrument temperature 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 calibrated two-dimensional (wavelength and spatial) FITS image spectra 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), the method for dark subtraction was revised which improved the calibration of the area under the anti-saturation filter by about 10%. New, time-dependent bad pixel maps were utilized, and the geometry was improved because the final kernels from the Deep Impact SPICE archive were used. The pipeline performed the following reduction and calibration steps to produce the two types of spectral images (uncleaned and cleaned radiance) in this data set: - Calibration of temperatures and voltages in the FITS headers - Decompression of compressed images - Linearization of raw data numbers - Subtraction of dark noise - Removal of electronic cross-talk (a unit correction) - 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'); Cosmic rays were not removed because the existing calibration routine was not robust The flat-field correction was not reliable and was not applied during the calibration process. The uncleaned radiance data, designated by the mnemonic 'RADREV', were provided in units of radiance as Watts/(meter**2 steradian micron) and were considered reversible because the calibration steps could be removed to get back to the original, raw data numbers. The irreversibly cleaned radiance data, designated by the mnemonic 'RAD', were provided in units of radiance as Watts/(meter**2 steradian micron). Only the RADREV data were included in version 1.0 of this data set. 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 FITS image extensions for a spectral registration (wavelength) map, a spectral resolution (bandwidth) map, and 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]. The reduced spectra were the best available data as of September 2006. There are known deficiencies for these spectra which are discussed in the HRII calibration limitations document 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 HIcccccccccc_eeeeeee_nnn_rr.LBL or FIT where cccccccccc is the spacecraft clock count at the mid-point of the observation and eeeeeee is the exposure ID (OBSERVATION_ID in data labels). Up to 999 individual images could be commanded for one exposure ID. Spectral scans often had 32 or more frames for one specific exposure. 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 9009001, the first FITS file name would be HIcccccccccc_9009001_001_RR.FIT and the last would be HIcccccccccc_9009001_032_RR.FIT. Finally, rr identifies the type of reduction: RR for RADREV data (radiance units, reversible) R for RAD data (radiance units, partially cleaned) Spectral Images --------------- The infrared spectral data were stored as FITS. The primary data array contains the two-dimensional spectral image, with the fastest varying axis corresponding to increasing wavelengths from 1.05 to 4.8 microns and the slowest varying axis corresponding to the spatial dimension. Each FITS file includes four image extensions that are two-dimensional pixel-by-pixel maps the provide additional information about the spectral (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 labels define the purpose of each bit. - The second extension provides the spectral registration or wavelength for each pixel in the primary image. This extension was required because the wavelength for each pixel changed as the temperature of the instrument increased or decreased. - The third extension provides the spectral bandwidth for each pixel in the primary image. This extension was required because the bandwidth for each pixel changed as the temperature of the instrument increased or decreased. - The fourth extension provides a signal-to-noise ratio for each pixel in the primary image. Each FITS file is accompanied by a detached PDS label. For more information about the FITS primary image and the 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. 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 Bin Mode Name (pix) (pix) Type Comments ---- ------ ------ ------ ----- ------------------------------- 1 BINFF 512 256 2x2 Binned full frame 2 BINSF1 512 126 2x2 Binned sub-frame 3 BINSF2 512 64 2x2 Binned sub-frame 4 UBFF 1024 512 1x1 Unbinned full frame 5 ALTFF 512 256 2x2 Alternate mode 1 (min. exposure time is 1/2 of mode 1) In this table, X-Size is the spectral dimension and Y-Size is the spatial dimension. 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. 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 PDS 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 to display an approach image of Tempel 1, 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 North is toward the left, and the Sun is down. Spectral Scans -------------- Nearly all exposures of Tempel 1 during encounter were scans across the nucleus or the coma, and these are identified in the HRII encounter pointing summary document. To make scans, the spacecraft was slewed while the IR detector recorded data. To work with spectral scans, it is recommended that all frames for one exposure ID be stacked into a three-dimensional cube. Then, a spatial-spatial map can be produced for a specific wavelength by selecting the appropriate spectral column from the image cube. Spectral wavelengths are provided by the second FITS extension, the spectral registration (wavelength) map. Several exposures from encounter were stares, where the spectrometer was pointed at a specific target location for the duration of the exposure. Exposure IDs that were stares are also identified in the HRII encounter pointing summary document included on the Deep Impact Documentation volume. IR Slit Location ---------------- For a comparison of the relative locations of the IR slit with respect to the fields of view of the Medium Resolution Instrument CCD (MRI) and the High Resolution Instrument CCD (HRI), see the relative boresight alignments section of the instrument calibration document. To visually inspect where the IR slit was estimated to be on the nucleus of Tempel 1 during impact and lookback, see the HRII/HRIV context maps included on the Deep Impact Documentation volume. Timing for Spectra ------------------ It is important to note that the readout order of the IR detector affects the timing of the spectra. When a HRII spectral image is displayed using the true-sky convention, the wavelength increases horizontally to the right and the spatial or along-slit direction is vertical. In this orientation, the IR detector was read out from the left and right edges and toward the center and starting with the first row at the bottom and ending with the last row at the top of the display. Since the detector was reset and read out on a pixel-by-pixel basis, the read out order affects the time at which each pixel was exposed, although each pixel had the same exposure duration. For more information about the timing of the spectra, see the IR focal plane and quadrant nomenclature sections of the instrument calibration document. Parameters : Data Units ---------- Reduced RADREV and RAD data are in units of radiance, W/(m**2 steradian micron). 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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| DATA_SET_RELEASE_DATE |
2006-12-22T00:00:00.000Z
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| START_TIME |
2005-06-20T09:08:55.414Z
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| STOP_TIME |
2005-07-06T06:17:45.267Z
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| MISSION_NAME |
DEEP IMPACT
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| MISSION_START_DATE |
2005-01-12T12:00:00.000Z
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| MISSION_STOP_DATE |
2005-07-13T12:00:00.000Z
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| TARGET_NAME |
9P/TEMPEL 1 (1867 G1)
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| TARGET_TYPE |
COMET
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| INSTRUMENT_HOST_ID |
DIF
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| INSTRUMENT_NAME |
DEEP IMPACT HIGH RESOLUTION INSTRUMENT - IR SPECTROMETER
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| INSTRUMENT_ID |
HRII
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| INSTRUMENT_TYPE |
INFRARED SPECTROMETER
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| NODE_NAME |
Small Bodies
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| ARCHIVE_STATUS |
SUPERSEDED
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| CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview : This data set, version 2.0, replaces version 1.0 that was delivered to PDS in December 2005. 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 report included on the Deep Impact Documentation volume. The FITS files in this data set were reviewed internally by the Deep Impact project and were used extensively by the science team. Review : This data set was peer-reviewed in April 2007 and was accepted for the PDS archive pending resolution of liens (completed in July 2007). Data Coverage and Quality : There are no gaps in this data set. All raw spectral images of Tempel 1 that were received on the ground were successfully reduced and 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 instrument calibration document. Limitations : Known Deficiencies for the IR Calibration ----------------------------------------- There are known deficiencies with the version of the IR calibration pipeline that reduced these data. The deficiencies are discussed in the HRII calibration limitations document included on the Deep Impact Documentation volume. Given these deficiencies, the most reliably calibrated pixels are outside the anti-saturation filter and between 2.0 and 4.6 microns. 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 significantly affect the HRII instrument. For more details, please see the instrument calibration paper by Klaasen, et al. (2006) [KLAASENETAL2006] included on the Deep Impact Documentation volume. 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 header pixels were included in the reduced FITS images. Since the values in these pixels vary dramatically, it is 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 instrument calibration paper included on the Deep Impact Documentation volume.
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| CITATION_DESCRIPTION |
McLaughlin, S. A., B. Carcich, T. McCarthy, M. Desnoyer, and K.P. Klaasen, DEEP IMPACT 9P/TEMPEL ENCOUNTER - REDUCED HRII SPECTRA V2.0, DIF-C-HRII-3/4-9P-ENCOUNTER-V2.0, NASA Planetary Data System, 2006.
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| ABSTRACT_TEXT |
This data set contains version 2.0 of calibrated spectral images of comet 9P/Tempel 1 acquired by the Deep Impact High Resolution Instrument Infrared Spectrometer during the encounter phase of the mission. Version 2.0 includes uncleaned and cleaned radiance data with improved calibration and geometry. The data were collected from 20 June through 6 July 2005.
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| PRODUCER_FULL_NAME |
STEPHANIE MCLAUGHLIN
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| SEARCH/ACCESS DATA |
SBN Comet Website
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