Data Set Overview : This data set contains reduced images of comet 9P/Tempel 1 acquired by the Deep Impact Impactor Target Sensor Visible CCD (ITS) after the impactor was released from the flyby spacecraft on July 3, 2005 UT.  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 ITS encounter data summary document which provides a log of the exposures beginning about 22 hours before impact.  A list of the comet observations in this data set is provided here:  Mid-Obs Exposure IDs Date DOY Minimum Maximum Mission Activity ---------- --- ------- ------- --------------------------------- 2005-07-03 184 9000026 9000043 Release, Continuous Comet Imaging 2005-07-03 184 9000060 9000128 Continuous Comet Imaging 2005-07-04 185 9000130 9000710 Continuous Comet Imaging, Impact   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] ITS_ENCOUNTER_DATA_SUMMARY.* : Image log beginning about 22 hours before impact 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  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:  DII-CAL-ITS-2-9P-CRUISE-V1.0 : Raw ITS cruise calibrations DII-C-ITS-2-9P-ENCOUNTER-V1.0 : Raw ITS encounter data DII-CAL-ITS-2-GROUND-TV3-V1.0 : ITS ground calibrations DI-C-SPICE-6-V1.0 : SPICE kernels   Processing : The reduced, 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. The pipeline performed the following reduction steps to produce the images 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) - Subtraction of a dark frame - Removal of electronic cross-talk removal - Application of a flat field - Normalization of quadrant gains - Removal of CCD transfer smear - Conversion of data numbers to units of radiance for an absolute, radiometric calibration  The resulting data were provided in physical units of radiance, Watts/(meter**2 steradian micron). These data, 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.  During the calibration process, the pipeline updated the pixel-by-pixel image quality map, the first FITS extension, so the following types of pixels could be identified:  - 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 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].  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, 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.   Compression ----------- 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 left, ecliptic North is up, and the Sun is to the right. This was also the convention used then displaying ITS images of Tempel 1 in published papers.  For a comparison of the orientation of ITS flight images with those from ground-based calibrations as well as those from the High and Medium Resolution Instrument CCDs (HRIV and MRI, respectively), see the quadrant nomenclature section of the 'Deep Impact Instrument Calibration' document.   File Naming Convention ---------------------- The naming convention for the image labels and FITS files is IVcccccccccc_iiiiiii_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 9009001, the two FITS files names would be IVcccccccccc_9009001_001_RR.FIT and IVcccccccccc_9009001_002_RR.FIT. Finally, RR identifies the reduction level, RADREV: reversible data in units of radiance (RADREV). This reduction level is described in the instrument calibration document.   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].  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 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.

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.   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 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 :  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 overclock rows and columns located around the edge of the image. The location of the header bytes in a FITS image depends on the readout order of the instrument, as discussed in the quadrant nomenclature section of the instrument calibration document.