Data Set Overview : This dataset contains calibrated images of comet 9P/Tempel 1 acquired by the Deep Impact Target Sensor (ITS) after the impactor was released from the flyby spacecraft on 03 July 2005.  Version 3.0 was calibrated by the EPOXI mission pipeline and includes corrected observation times and a revision to how the camera's compressed zero-DN lookup table entry is decoded. The EPOXI pipeline corrected the interpretation of microsecond counter of the spacecraft clocks which introduced maximum errors of about 40 milliseconds in the earlier Versions 2.0 and 1.0 of this dataset that were produced by the Deep Impact pipeline. The EPOXI pipeline was also changed to decompress the visual CCD camera's zero-DN lookup table entry to the top of its range, which is 350 DN, and flag the affected pixels as saturated. Finally for Version 3.0, the I-over-F data products archived in Version 2.0 were replaced by multiplicative constants supplied in the headers for converting radiance products to I-over-F, and the EPOXI convention for constructing PRODUCT_IDs and data file names was used. For more information see the EPOXI Calibration Pipeline Summary document in this dataset and Klaasen, et al. (2013) [KLAASENETAL2011].  A summary of the comet observations in this dataset 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  The 9P/Tempel 1 data are described in 'Deep Impact: The Anticipated Flight Data' by Klaasen, et al. (2005) [KLAASENETAL2005]. Initial results from the encounter and impact were presented in 'Deep Impact: Excavating Comet Tempel 1' by by A'Hearn, et al. (2005) [AHEARNETAL2005A].   Required Reading --------------- The documents listed below are essential for the understanding and interpretation of this dataset. Although a copy of each document is provided in the DOCUMENT directory of this dataset, the most recent version is archived in the Deep Impact and EPOXI documentation set, DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V4.0, available online at http://pds.nasa.gov.  EPOXI_SIS.PDF - The Archive Volume and Data Product Software Interface Specifications document (SIS) describes the EPOXI datasets including this Deep Impact dataset recalibrated by the EPOXI pipeline, the science data products, and defines keywords in the PDS labels.  EPOXI_CAL_PIPELINE_SUMM.PDF - The EPOXI Calibration Pipeline Summary provides an overview of the final version of the calibration pipeline that generated the data products in this dataset. For a thorough discussion of the pipeline, see 'EPOXI Instrument Calibration' by Klaasen, et al. (2013) [KLAASENETAL2011].  CALIBRATION_PAPER_DRAFT.PDF - This incomplete draft of 'Deep Impact Instrument Calibration' by Klaasen, et al. (2008) [KLAASENETAL2006] explains how the instruments were calibrated for the Deep Impact mission. It also describes the Deep Impact calibration pipeline, which was the basis for the EPOXI calibration pipeline.  INSTRUMENTS_HAMPTON.PDF - The Deep Impact instruments paper by Hampton, et al. (2005) [HAMPTONETAL2005] provides very detailed descriptions of the instruments.  ITS_ENCOUNTER_DATA_SUMMARY.PDF - This log provides notes and data quality recorded by the science team for each ITS image, beginning about 22 hours before impact.  ITS_3_4_DI_TEMPEL1.TAB - This ASCII table provides image parameters such as the mid-obs Julian date, exposure time, image mode, filter, mission activity type, and description or purpose for each observation (i.e., data product) in this dataset. This file is very useful for determining which data files to work with.   Related Data Sets ----------------- The following PDS datasets are related to this one and may be useful for research:  DII-CAL-ITS-2-GROUND-TV3-V1.0 - Raw ITS pre-flight thermal-vacuum calibration images  DII-CAL-ITS-2-9P-CRUISE-V1.0 - Raw ITS cruise calibration images  DII-C-ITS-2-9P-ENCOUNTER-V1.0 - Raw ITS images of comet Tempel 1  DI-C-SPICE-6-V1.0 - Deep Impact SPICE kernels  DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V4.0 - Deep Impact and EPOXI documentation set   Processing : The calibrated two-dimensional FITS CCD images and PDS labels in this dataset were generated in late 2013 by the EPOXI data pipeline, maintained by the project's Science Data Center (SDC) at Cornell University. Known limitations and deficiencies of the pipeline and the resulting data are discussed in the EPOXI Calibration Pipeline Summary document in this dataset and by Klaasen, et al. (2013) [KLAASENETAL2011] and in 'Deep Impact Instrument Calibration' by Klaasen, et al. (2008) [KLAASENETAL2006].  For each CCD image, the pipeline generates two types of calibrated products:  - Uncleaned radiance data provided in units of Watts/(meter**2 steradian micron) and identified by the mnemonic 'RADREV'. The RADREV data are considered to be reversible because the calibration steps can be backed out to return to the original, raw data numbers. A RADREV image can be converted to unitless I-over-F by multiplying by the value assigned to the DATA_TO_IOVERF_MULTIPLIER keyword in the PDS label. Alternatively, a RADREV image can be converted from radiance units to calibrated data numbers by multiplying by the value assigned to the DATA_TO_DN_MULTIPLIER in the PDS label.  - Irreversibly cleaned radiance data provided in units of Watts/(meter**2 steradian micron) and identified by the mnemonic 'RAD'. The RAD data are considered to be irreversible because the calibration steps, such as smoothing over bad pixels, cannot easily be backed out to return to the original, raw data numbers. A RAD image can be converted to unitless I-over-F by multiplying by the value assigned to the DATA_TO_IOVERF_MULTIPLIER keyword in the PDS label. Alternatively, a RAD image can be converted from radiance units to calibrated data numbers by multiplying by the value assigned to the DATA_TO_DN_MULTIPLIER in the PDS label (though interpolated pixels will not be real data). Please note that values in the overclock rows and columns bordering the active CCD area are set to 0 in the RAD product.  The calibration pipeline performed the following processes, in the order listed, on the raw FITS data to produce the RADREV and RAD products found in this dataset (the process uses the image mode and filter to select the appropriate set of calibration files):  - Decompression of compressed raw images (compression was performed on board the spacecraft and the resulting data were downlinked) - Correction for bias - Subtraction of a dark frame - Removal of horizontal, instrumental striping; this step was *not* applied to the calibrated images in this dataset because the science team determined this step degraded the images; to indicate destriping was not performed, RMSTRIPE is set to F (false) in the FITS headers and all values in the DESTRIPE extension are set to 0 - Removal of electronic cross-talk - Application of a normalized flat field - Removal of CCD transfer smear - Conversion of data numbers to units of radiance for an absolute, radiometric calibration that is reversible (RADREV) - Interpolation over bad and missing pixels identified in the RADREV data to make a partially cleaned, irreversible, radiometric calibration with units of radiance (RAD); Steps for despiking (i.e., cosmic ray removal) and denoising the data which are part of the RAD stream were not performed because the existing routines are not robust - Calculation of multiplicative factors to convert a RADREV or RAD image to I-over-F  As part of the calibration process, the pipeline updated the pixel-by-pixel image quality map, the first FITS extension, to identify:  - 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, and - Pixels considered to be anomalous as indicated by bad pixel maps (missing pixels were identified when the raw FITS files were created).  The pipeline also created a FITS image extension to capture the signal-to-noise ratio map and another extension to capture the values used to remove horizontal striping. The calibration steps and files applied to each raw image are listed in the PROCESSING_HISTORY_TEXT keyword in the PDS data label.   Data :  FITS Images and PDS Labels -------------------------- Each calibrated image is stored as FITS. The primary data unit contains the two-dimensional CCD image which is followed by two image extensions that are two-dimensional pixel-by-pixel maps providing additional information about the CCD image:  - The first extension uses one byte consisting of eight, single-bit flags to describe the quality of each pixel in the primary image. The PDS data label defines the purpose of each single-bit flag.  - The second extension provides a signal-to-noise ratio for each pixel in the primary image.  - The third extension contains the two columns of DN values that were subtracted from every non-overclock column in the left and right halves of the primary image array by the stripe removal process. However for all images in this dataset, all values in the DESTRIPE extension are set to 0 because this step was not applied.  Each FITS file is accompanied by a detached PDS data label. The EPOXI SIS document provides definitions for the keywords found in a data label and provides more information about the FITS primary image and the extensions. Many values in a data label were extracted from FITS image header keywords which are defined in the document EPOXI_FITS_KEYWORD_DESC.ASC found in the Deep Impact and EPOXI documentation dataset, DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V4.0.   File Naming Convention ---------------------- The naming convention for the data labels and FITS files is IVyymmddhh_eeeeeee_nnn_rr.LBL or FIT where 'IV' identifies the ITS instrument, yymmddhh provides the UTC year, month, day, and hour at the mid-point of the observation, eeeeeee is the exposure ID (OBSERVATION_ID in data labels), nnn provides the image number (IMAGE_NUMBER in the data labels) within the exposure ID, and rr identifies the type of reduction:  RR for RADREV data (reversibly calibrated, radiance units) R for RAD data (partially cleaned RADREV data, radiance units)  Up to 999 individual images or frames can be commanded for one exposure ID. 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 this dataset, all frames numbers (nnn) are 001 because only one frame was commanded for each exposure ID.  This convention is the one used by the EPOXI pipeline to construct data product file names and PRODUCT_IDs. To translate between the EPOXI and Deep Impact conventions, refer to the ITS_TRANSLATE_PRODUCT_ID.LBL and ITS_TRANSLATE_PRODUCT_ID.TAB files located in the DOCUMENT directory of this dataset.   Image Compression ----------------- All calibrated data products are uncompressed. If an associated raw data product was compressed on board the impactor spacecraft (and thus received on the ground and archived as compressed) then the calibration pipeline used one of four 8-bit lookup tables to decompress the raw image. For more information, see the EPOXI Calibration Pipeline Summary document as well as Hampton, et al. (2005) [HAMPTONETAL2005], Klaasen, et al. (2008) [KLAASENETAL2006] and Klaasen, et al. (2013) [KLAASENETAL2011].   Image Orientation ----------------- A true-sky 'as seen by the observer' view is achieved by displaying the image using the standard FITS convention: the fastest-varying axis (samples or wavelength) increasing to the right in the display window and the slowest-varying axis (lines or spatial/along-slit) increasing to the top. This convention is identified in the data labels: the SAMPLE_DISPLAY_DIRECTION keyword is set to RIGHT and LINE_DISPLAY_DIRECTION to UP.  The direction to celestial north, ecliptic north, and the Sun is provided in data labels by CELESTIAL_NORTH_CLOCK_ANGLE, ECLIPTIC_NORTH_CLOCK_ANGLE, and SUN_DIRECTION_CLOCK_ANGLE keywords and are measured clockwise from the top of the image when it is displayed in the correct orientation as defined by SAMPLE_DISPLAY_DIRECTION and LINE_DISPLAY_DIRECTION. Please note the aspect of the North celestial pole in an image can be computed by adding 90 degrees to the boresight declination given by DECLINATION in the data labels.  Using this convention for ITS 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 when displaying ITS images of Tempel 1 in published papers.  For a comparison of the orientation of ITS in-flight images with those from ground-based calibrations and from the High and Medium Resolution Instrument CCDs (HRIV and MRI, respectively), see the quadrant nomenclature section in Klaasen, et al. (2008) [KLAASENETAL2006].   Parameters :  Data Units ---------- The calibrated RADREV and RAD image data have units of radiance, W/(m**2 steradian micron).   Imaging Modes ------------- A summary of the imaging modes is provided below. For more information see Hampton, et al. (2005) [HAMPTONETAL2005], Klaasen, et al. (2008) [KLAASENETAL2006] and Klaasen, et al. (2013) [KLAASENETAL2011]. All modes are unbinned.  X-Size Y-Size Mode Name (pix) (pix) Comments ---- ------ ------ ------ --------------------------------------- 1 FF 1024 1024 Full frame, shuttered 2 SF1 512 512 Sub-frame, shuttered 3 SF2S 256 256 Sub-frame, shuttered 4 SF2NS 256 256 Sub-frame, not shuttered 5 SF3S 128 128 Sub-frame, shuttered 6 SF3NS 128 128 Sub-frame, not shuttered 7 SF4O 64 64 Sub-frame, not shuttered 8 SF4NO 64 64 Sub-frame, not shuttered, no overclocks 9 FFD 1024 1024 Full-frame diagnostic, shuttered   Time- and Geometry-Related Keywords ----------------------------------- All time-related keywords in the data labels, except EARTH_OBSERVER_MID_TIME, are based on the clock on board the impactor spacecraft. EARTH_OBSERVER_MID_TIME provides the UTC when an Earth-based observer should have been able to see an event recorded by the instrument.  The SDC pipeline was not able to automatically determine the proper geometric information for the target of choice in some cases. When these parameters could not be computed, the corresponding keywords in the data labels are set to a value of unknown, 'UNK'. Also if GEOMETRY_QUALITY_FLAG is set to 'BAD' or GEOMETRY_TYPE is set to 'PREDICTED' in the PDS labels, then this indicates the geometry values may not be accurate and should be used with caution. The value 'N/A' is used for some geometry-related keywords in the data labels because these parameters are not applicable.  Observational geometry parameters provided in the data labels were computed at the epoch specified by the mid-obs UTC, IMAGE_MID_TIME, in the data labels. The exceptions are the target-to-sun values evaluated at the time light left the target that reached the spacecraft at mid-obs time, and the earth-observer-to-target values evaluated at the time the light that left the target, which reached the spacecraft at mid-obs time, reached Earth.   Ancillary Data : The timing and geometric parameters included in the data labels and FITS headers were computed using the final version of the kernel files archived in the Deep Impact SPICE dataset DI-C-SPICE-6-V1.0.   Coordinate System : Earth Mean Equator and Vernal Equinox of J2000 (EME J2000) is the inertial reference system used to specify observational geometry parameters in the data labels.   Software : The observations in this dataset are in standard FITS format with PDS labels, and can be viewed by a number of PDS-provided and commercial programs. For this reason no special software is provided with this dataset.

Confidence Level Overview : The data files in this data set were reviewed internally by the EPOXI project.   Review : This dataset was peer reviewed and certified for scientific use on 21 March 2014.   Data Coverage and Quality : There are no unexpected gaps in this dataset. All observations received on the ground were processed and included in this dataset.  Any dark horizontal patches or stripes through some images indicate 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 EPOXI SIS document.   Limitations :  Timing ------ 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, see the Deep Impact Spacecraft Clock Correlation report, SCLK_CORRELATION.ASC, provided on the Deep Impact and EPOXI documentation dataset, DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V4.0.  The EPOXI project plans to generate a complete and highly accurate set of UTC correlations since launch. This will ultimately result in a future version of a SCLK that will retroactively change correlation for **all** Deep Impact and EPOXI data. When this kernel is available, it will be added to the SPICE data sets for the two missions and posted on the NAIF/SPICE web site at http://naif.jpl.nasa.gov/naif/.   CCD Horizontal Gap ------------------ Calibration analysis combining Deep Impact and early EPOXI data determined the two halves of the visible CCDs - the boundary being the two horizontal central lines 511 and 512 (zero based) - while physically consistent across the boundary, are 1/6 of a pixel smaller vertically than a normal row. Therefore, reconstructed images, which have uniform row spacing, have a 1/3-pixel extension introduced at the center of the array. Thus for two features on either side of the midpoint line, the vertical component of the actual angular separation between those features is one-third of a pixel less than their measured difference in vertical pixels in the image. As for all geometric distortions, correction of this distortion will require resampling of the image and an attendant loss in spatial resolution. The standard pipeline process does not perform this correction so as to preserve the best spatial resolution.  The two 1/6-pixel narrower central rows collect only 5/6 of the charge of a normal row. This effect is corrected by the flat-field division for calibrated science images so that the pixels in these rows have the correct scene radiance assigned to them. However, point-source or disk-integrated photometric measurements using aperture photometry areas that include these central rows will be slightly distorted unless special adjustments are made. For example, the aperture photometry process for comet 9P/Tempel 1 added an extra 1/6-pixel worth of signal to the to the pixels in each of these two rows in the reconstructed, calibrated images as described in Appendix A of Belton, et al. (2011) [BELTONETAL2011].   Displaying Images ----------------- Flight software writes an image header over the first 100 bytes of quadrant A. These image header pixels were included in the calibrated FITS images. Since the values in these pixels vary dramatically, it is recommended that the values of the EPOXI:MINIMUM and EPOXI:MAXIMUM keywords in the 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 CCD image. For more information, see the quadrant nomenclature section of the EPOXI SIS document.