Data Set Information
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| DATA_SET_NAME |
DEEP IMPACT 9P/TEMPEL ENCOUNTER - REDUCED HRII SPECTRA V1.0
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| DATA_SET_ID |
DIF-C-HRII-3/4-9P-ENCOUNTER-V1.0
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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 reduced 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. Spectra taken before June 20, 2005, are not included in this data set because the spectrometer was not pointing at the target. The 9P/Tempel 1 spectra are described in 'Deep Impact: The Anticipated Flight Data' by Klaasen, et al. (2005) [KLAASENTAL2005]. For more details about the spectra taken around impact, refer to the HRII encounter data summary document which provides a log of the exposures taken from 28 hours before impact through lookback. Also, refer to the HRII encounter pointing summary document which describes the pointing and scan direction for exposures taken at encounter. A list of the reduced spectra in this data sets 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 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_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_CALIBRATION_LIMITATIONS.* : Discusses known deficiencies in the IR calibration process that reduced the spectral images CALIBRATION_DOC.* : Instrument calibration by Klaasen, et al. (2006) [KLAASENETAL2006] CALIBRATION_SOFTWARE/AADICAL.LBL: Calibration pipeline IDL software provided as documentation INFLIGHT_CALIBRATION_SUMMARY.* : Summary of in-flight calibrations 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 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-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 reduced, two-dimensional FITS 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. The pipeline performed the following reduction steps to produce the spectra in this data set: - Calibration of temperatures and voltages in the FITS headers - Decompression of compressed images - Correction for uneven bit weighting due to analog-to-digital (ADC) conversion (a unit correction) - Linearization of raw data numbers - Subtraction of dark noise - Removal of electronic cross-talk removal (a unit correction) - Normalization of quadrant gains (a unit correction) - Application of a flat field (a unit correction) - Conversion of data numbers to units of radiance for an absolute, radiometric calibration The resulting spectra were provided in physical units of radiance, Watts/(meter**2 steradian micron). These spectra, designated by the pneumonic ''RADREV'', were not cleaned and are considered reversible because the calibration steps can be removed to get back to the original, raw data numbers. The data were not cleaned for cosmic rays because the automated routine could not handle all cases as of this archive. 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 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 spectral image are listed in the PROCESSING_HISTORY_TEXT keyword in the PDS data label. The reduced spectra were the best available data as of November 2005. There are known deficiencies for these spectra which are discussed in the HRII calibration limitations document. For a detailed discussion of the calibration pipeline used to reduce these data, see the instrument calibration document by Klaasen, et al. (2006) [KLAASENETAL2006]. 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 (1.05 to 4.8 microns) and the slowest varying axis providing the spatial dimension. Each FITS file includes four image extensions that are pixel-by-pixel maps providing 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 labels define the purpose of each bit. - The second extension provides the spectral registration or wavelength for each pixel in the primary image. Each image requires a specific wavelength map because the wavelength changed with temperature. - The third extension provided the spectral resolution or bandwidth for each pixel in the primary image. Each image requires a specific spectral resolution map because the bandwidth changed with temperature. - The fourth extension provides a signal-to-noise ratio for each pixel in the primary image. Each spectral image 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. Compression ----------- The calibration pipeline used one of four lossy lookup tables to decompress raw spectral 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 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. 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. 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. 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. File Naming Convention ---------------------- The naming convention for the data labels and FITS files is HIcccccccccc_iiiiiii_nnn_RR.LBL or FIT where cccccccccc is the spacecraft clock count at the mid-point of the observation and iiiiiii 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 reduction level, RADREV: reversible data in units of radiance. Parameters : Data Units ---------- Reduced ''RADREV'' data are in units of radiance, W/(m**2 steradian micron). The data are reversible and are not cleaned. 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, as published by A'Hearn, et al. (2005) [AHEARNETAL2005A]. 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). Geometric parameters were computed using the best SPICE kernels available at the time of calibration and the results were stored in the FITS header. For impact images, geometric parameters such as the target-to-spacecraft distance were computed with respect to the impact site, not the center of the comet. 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. 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. The improved kernels were 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. The SPICE kernels used to calculated the geometric parameters are provided by the SPICE_FILE_NAME keyword in the PDS data labels. The kernels are listed in the order they were loaded into memory for processing. 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 kernels were improved, and these were 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 |
2005-12-31T00:00:00.000Z
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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 : 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 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 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 : There are no gaps in this data set. All raw, Tempel 1 spectral images 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. For example, the dark subtraction process was not robust. A better method was implemented in early 2006, after these data were delivered to SBN for a peer review, which improved the calibration of the anti-saturation filter by about 10%. The project plans to archive these improved data into PDS as version 2.0 of this data set. This and other deficiencies are described in the HRII calibration limitations document. Given the known deficiencies of the reduced spectra in this data set, the most reliably calibrated pixels are those outside the anti-saturation filter from 2.0 to 4.8 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 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 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 Deep Impact instrument calibration document.
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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 V1.0, DIF-C-HRII-3/4-9P-ENCOUNTER-V1.0, NASA Planetary Data System, 2005.
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| ABSTRACT_TEXT |
This data set contains reduced spectral images of 9P/Tempel 1 acquired by the Deep Impact High Resolution Instrument Infrared Spectrometer during the encounter phase of the mission.
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| PRODUCER_FULL_NAME |
STEPHANIE MCLAUGHLIN
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| SEARCH/ACCESS DATA |
SBN Comet Website
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