Data Set Overview : This dataset contains calibrated images of comet 103/P Hartley 2 acquired by the Medium Resolution Visible CCD (MRI) from 05 September through 26 November 2010 during the Hartley 2 encounter phase of the EPOXI mission. Clear-filter and CN images of the comet were acquired throughout this phase; OH, C2, and dust continuum images were only acquired for several days spanning closest approach. Initial results based on these data are discussed by A'Hearn, et al. (2011) [AHEARNETAL2011].  The following list summarizes the comet observations in this dataset. Descriptive text for each activity is included below. Additionally, the MRI Hartley 2 Flyby (E-18 hours to E+2 days) Log in the DOCUMENT directory provides the imaging sequence and notes about image quality that were recorded by the science team as the data arrived on the ground.  -------------------------------------------------------------------------- Mid-Obs Exposure IDs Mission Activity Date/DOY Min Max (E : Encounter) -------------- ------- ------- ---------------------------------------- 2010-09-05/248 4000000 4000018 Approach imaging E-60 to E-50 days; to Rotation sampling every 6 hrs in Clear1 2010-09-15/258 and CN filters; ExpIDs repeated daily  2010-09-15/258 4000000 4000047 Approach imaging E-50 to E-40 days; to Rotation sampling every 2 hrs in Clear1 2010-09-25/269 and CN filters; ExpIDs repeated daily  2010-10-01/274 4000000 4000463 Approach imaging E-34 to E-8 days; to Clear1 rotation sampling every 5 min; 2010-10-27/300 CN filter ~every hour; Clear1 context frames for HRII scans; ExpIDs repeated daily*  2010-10-27/300 4000000 4000470 Approach imaging E-8 days to E-18 hours; to 5000000 5000074 Clear1 continuous rotation sampling for 2010-11-03/307 6000000 6000011 16 hours then once every hour; 5 CN frames daily, 4 OH frames daily, and 2 Dust frames daily; ExpIDs repeated daily**  2010-11-03/307 4000100 4000637 Flyby imaging E-18 to E-3 hours; to Clear1 rotation sampling every 30 min; 2010-11-04/308 CN, OH, C2 filters every hour plus occasional dust continuum ExpIDs are not repeated  2010-11-04/308 5000000 5008001 Flyby imaging E-2 to E+1.5 hours; Clear1 imaging every 15 min to nearly continuous at closest approach; CH, OH, C2, IR, Red, and dust continuum imaging 2 full color filter sets with 2 additional sets of Red and IR ExpIDs are not repeated  2010-11-04/308 4000800 4010103 Flyby imaging E+2 hours to E+2 days to Clear1 rotation sampling every 30 min; 2010-11-06/310 CN, OH, C2 filters every hour plus occasional dust continuum Clear1 context frames for HRII scans; ExpIDs are not repeated  2010-11-06/310 4100000 4500184 Departure imaging E+2 to E+12 days; to Clear1 continuous rotation sampling; 2010-11-16/320 5 CN and OH frames daily; Clear1 context frames for HRII scans; ExpIDs repeated daily  2010-11-16/320 4100000 4500018 Departure imaging E+12 to E+21 days; to Clear1 rotation sampling every 30 min; 2010-11-26/330 5 CN frames daily; Clear1 context frames for HRII scans; ExpIDs repeated daily -------------------------------------------------------------------------- * Data acquired on 06 Oct were never downlinked due to a pointing problem with the Deep Space Network (DSN). ** First cycle of 28 Oct, only six hourly scans were taken before the sequence stopped and restarted at 'dosido' section for 7 hourly scans. Therefore the middle 11 scans were not acquired on purpose. Some frames in a scan may be missing because they were scheduled for transmission after the HGA was turned off, i.e. loss of signal. Any data the DSN received after this were considered extra credit.  Hartley 2 Approach Imaging, E-60 to E-50 Days (VIS only): The MRI and HRIV visible CCDs began imaging 103P/Hartley 2 every six hours on 05 September 2010, 60 days before the encounter (E-60 days) encounter and continued for 10 days. However due to thermal issues with a traveling wave tube amplifier the entire HRI system including the HRIV CCD was turned off on 06 September until 20 September. MRI continued its imaging sequence as planned through E-50 days. The comet was observed for 16 hours at a time with 8 hours devoted to downlinking the data.  Hartley 2 Approach Imaging, E-50 to E-40 Days (VIS only): From 15 to 25 September 2010, the imaging cadence for MRI increased to every two hours. On 20 September the HRIV CCD was turned on, and it begin imaging 103P/Hartley 2 once every two hours for the duration of the period. The comet was observed for 16 hours at a time with 8 hours devoted to downlinking the data.  Hartley 2 Approach Imaging, E-34 to E-8 Days (Start HRII): From 01 to 28 October 2010, MRI and HRIV imaged 103P/Hartley 2 about every 5 minutes while the HRII spectrometer scanned for outbursts once every 30 minutes. The instruments observed the comet for 16 hours per day allowing for 8 hours of downlinking; the same sequence was repeated daily yielding one full cycle per day. Data from the 6th cycle on 06 October 2010 (DOY 279) were never downlinked because of a pointing problem with the Deep Space Network. Those data had to be erased on board the spacecraft to make room for the next daily cycle and could not be recovered.  Hartley 2 Approach Imaging, E-8 Days to E-18 Hours: From 28 October to 03 November 2010, the MRI and HRIV imaged 103P/Hartley 2 continuously and HRII scanned the comet about every hour for 16 hours per day allowing for 8 hours of downlinking punctuated by hourly maneuvers, called dosido, to observe the comet. During this imaging phase there was only a single downlink of all images with zero margin; thus some images were occasionally lost as expected. The first cycle (DOY 300/301) was abbreviated such that the first comet-imaging session was only 6-hours long, followed by the standard 8-hour dosido.  Hartley 2 Encounter Imaging, E-18 hours to E+2 Days: From 03 to 06 November 2010, the HRII, HRIV, and MRI performed high resolution encounter imaging of 103P/Hartley2. The HRIV and MRI instruments began sampling about once every two hours until one hour before encounter when the cadence changed to once every 15 minutes. At E-30 minutes the instruments began continuously imaging of the comet. At E+30 minutes simultaneous observing and data playback began with samples being taken every 30 minutes. During the encounter imaging period, HRII infrared scans occurred every two hours until four hours prior to encounter when the cadence increased to hourly then more frequently one hour before closest approach. About one hour after closest approach, regular infrared sampling at 30-minute intervals resumed.  On 04 November near closest approach, MRI obtained two, contiguous, full color sets (CN, OH, C2, IR, Red, and dust continuum filters) at a scale < 550 m/pixel (the exposure IDs are provided):  5002027 - 5002036 (E-09 min, Full Frame/Mode 1, ~83-70 m/pixel) 5006057 - 5006065 (E+09 min, Full Frame/Mode 1, ~83-70 m/pixel)  Also on 04 November, MRI obtained broadband, clear-filter images of the nucleus with a scale < 10 m/pixel:  6000001 (E-35 sec, Full Frame/Mode 1, ~8 m/pixel) 5004046 (E-06 sec, Full Frame/Mode 1, ~7 m/pixel) 6000002 (E-01 sec, Full Frame/Mode 1, ~7 m/pixel) 5004051 (E+03 sec, Full Frame/Mode 1, ~7 m/pixel) 6000003 (E+37 sec, Full Frame/Mode 1, ~8 m/pixel)  Although there was an error in how the spacecraft was commanded to point during closest approach the nucleus remained in the field of view of all MRI frames acquired at that time.  Hartley 2 Departure Imaging, E+2 to E+12 Days: From 06 to 16 November 2010, the HRII spectrometer scanned 103P/Hartley 2 every ~15 minutes while the MRI CCD imaged the comet every 2 minutes and HRIV once every hour.  Hartley 2 Departure Imaging, E+12 to E+21 Days: From 16 to 26 November 2010, the HRII spectrometer scanned 103P/Hartley 2 every 30 minutes, and HRIV performed rotation sampling at the same cadence. MRI performed rotation sampling every 30 minutes and imaging using gas filters every two to four hours.   Filter Usage ------------ Although filter usage is given in the observations table above, it is summarized here:  Filter# Filter(s) Usage dates ------- ---------------- ------------------------------------ 1 Clear1 E-60 to E+21 days (DOY 248-330) 2 C2 E-18 hours to E+2 days (DOY 307-310) 3 Green Continuum E-8 to E+2 days (DOY 300-310) 7 CN E-60 to E+21 days (DOY 248-330) 8 Violet Continuum E-8 to E+2 days (DOY 300-310) 9 OH E-8 to E+12 days (DOY 300-320) 1-9 Full set* E-2 to E+1.5 hours (DOY 308) --------------------------------------------------------------- * Full set includes Red (#4) and IR (#5) filters; Clear #6 was not used; includes two additional sets of Red and IR.   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-V3.0, 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, the science data products, and defines keywords in the PDS labels.  HARTLEY2_CAL_PIPELINE_SUMM.PDF - The EPOXI Hartley 2 Calibration Pipeline Summary provides an overview the calibration pipeline as of June 2011 used for processing data acquired during the Hartley 2 Encounter. The document also discusses known limitations of the calibration pipeline with respect to the HRII, HRIV, and MRI instruments. For a thorough discussion of the pipeline refer to EPOXI Instrument Calibration by Klaasen, et. al. (2011, in preparation) [KLAASENETAL2011].  INSTRUMENTS_HAMPTON.PDF - The Deep Impact instruments paper by Hampton, et al. (2005) [HAMPTONETAL2005] provides very detailed descriptions of the instruments.  MRI_HARTLEY2_FLYBY_LOG.PDF - This log provides notes recorded by the science team as each Flyby exposure (scan) acquired from E-18 to E+48 hours was received on the ground. Annotations include data quality and a list of frames within each scan that appeared to contain the comet.  MRI_3_4_EPOXI_HARTLEY2.TAB - This ASCII table provides image parameters such as the mid-obs Julian date, exposure time, 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 calibration purposes:  DIF-C-MRI-2-EPOXI-HARTLEY2-V1.0 - Raw MRI images of comet Hartley 2  DIF-CAL-MRI-2-EPOXI-CALIBRATIONS-V2.0 - Raw MRI in-flight calibrations from 2007 to 2011  DIF-C-HRII-2-EPOXI-HARTLEY2-V1.0 DIF-C-HRII-3/4-EPOXI-HARTLEY2-V1.0 - Raw and calibrated HRII spectral images of Hartley 2  DIF-C-HRIV-2-EPOXI-HARTLEY2-V1.0 DIF-C-HRIV-3/4-EPOXI-HARTLEY2-V1.0 - Raw and calibrated HRIV images of comet Hartley 2  DIF-C/E/X-SPICE-6-V1.0 - EPOXI SPICE kernels  DIF-CAL-HRII/HRIV/MRI-6-EPOXI-TEMPS-V2.0 - HRII, HRIV, and MRI instrument thermal telemetry data for EPOXI which may be useful for determining how temperature fluctuations affect the science instruments, in particular the IR spectrometer  DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V3.0 - Deep Impact and EPOXI documentation set including a draft of the Deep Impact instrument calibration paper by Klaasen, et al. (2008) [KLAASENETAL2006]   Processing : The calibrated two-dimensional FITS CCD images and PDS labels in this data set were generated by the Deep Impact/EPOXI data pipeline, maintained by the project's Science Data Center (SDC) at Cornell University. The version of the pipeline used to calibrate these data was the best available as of June 2011. Known limitations and deficiencies of the pipeline and the resulting data are discussed in the EPOXI Hartley 2 Calibration Pipeline Summary document in this dataset or by Klaasen, et al. (2011, in preparation) [KLAASENETAL2011].  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 MRI FITS data to produce the RADREV and RAD products found in this data set (the process uses the image mode and filter to select the appropriate set of calibration files):  - Decompression of compressed images - Correction for bias - Subtraction of a dark frame - Removal of horizontal, instrumental striping - 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 MRI 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 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.  - 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.  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-V3.0.   File Naming Convention ---------------------- The naming convention for the raw data labels and FITS files is MVyymmddhh_eeeeeee_nnn_rr.LBL or FIT where 'MV' identifies the MRI 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 example, if 7 frames were commanded for a scan with an exposure ID of 4000001, the first FITS file name would be MV10090513_4000001_001_RR.FIT and the last would be MV10090513_4000001_007_RR.FIT.   Image Compression ----------------- All calibrated data products are uncompressed. If an associated raw data product 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 8-bit lookup tables to decompress the raw image. See the EPOXI SIS and EPOXI Hartley 2 Calibration Pipeline Summary documents as well as Klaasen, et al. (2008) [KLAASENETAL2006] for more information.   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 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.  For a comparison of the orientation FITS image data from the three science instruments, see the quadrant nomenclature section of the the EPOXI SIS document.   Instrument Alignment -------------------- For a comparison of the field of view and the relative boresight alignment of MRI to the High Resolution Instrument Visible CCD (HRIV) and the slit of the High Resolution IR Imaging Spectrometer (HRII), see the instrument alignment section of the EPOXI SIS document or Klaasen, et al. (2011) [KLAASENETAL2011].   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 here. For more information see the EPOXI SIS and EPOXI Hartley 2 Calibration Pipeline Summary documents, Hampton, et al. (2005) [HAMPTONETAL2005] and Klaasen, et al. (2011) [KLAASENETAL2011].  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  All modes are unbinned. Most image modes have 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. These overclock areas described in the Deep Impact instruments document and the Deep Impact instrument calibration document.   Filters ------- A summary of the MRI filters is provided here. For more information see the EPOXI SIS and EPOXI Hartley 2 Calibration Pipeline Summary documents, Hampton, et al. (2005) [HAMPTONETAL2005] and Klaasen, et al. (2011) [KLAASENETAL2011].  Filter Center Width # Name (nm) (nm) Comments - ---------- ----- ----- ------------------------------- 1 CLEAR1 650 >700 For context; not band limited 2 C2 514 11.8 For C2 in coma 3 GREEN_CONT 526 5.6 For dust in coma 4 RED 750 100 For context 5 IR 950 100 For context; longpass 6 CLEAR6 600 >700 For context; not band limited 7 CN 387 6.2 For CN in coma 8 VIOLET_CONT 345 6.8 For dust in coma 9 OH 309 6.2 For OH in coma   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 flyby 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 for certain calibration targets.  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 geometric parameters included in the data labels and FITS headers were computed using the best available SPICE kernels at the time the data products were generated. The kernels are archived in the EPOXI SPICE dataset, DIF-C/E/X-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 FITS files in this dataset were reviewed internally by the EPOXI project and were used extensively to verify the calibration of the instrument.   Review : This dataset was peer reviewed and certified for scientific use on 15 August 2011.   Data Coverage and Quality : There are no unexpected gaps in this dataset, except those that occurred on 06 and 28 October 2011 as noted in the dataset overview. All science frames received on the ground were processed and included in this dataset.  Some frames (exposures IDs) in this dataset are repeatedly smeared because the spacecraft was in motion due to an HRII spectrometer scan.  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 EPOXI SIS document.   Limitations :  Timing ------ The flyby spacecraft clock SPICE kernels (SCLK) used to convert to UTC and to calculate geometry-related parameters for this dataset have a known accuracy of no better than 0.5 seconds. However the latest SCLK (science version 84) applied to the Hartley 2 encounter data is good to within 0.01 seconds for converting the spacecraft timestamps to ephemeris time for observations acquired around closest approach. Please note that the SCLK (version 65) used to compute UTC values and geometry for calibration data acquired from January 2009 through July 2010 has known discontinuities of up to a second. Those discontinuities have been corrected in the latest SCLK, science version 84, applied to Hartley data.  The mission operations team has figured out how to correct raw clock correlation data for the Deep Impact flyby spacecraft to allow timing fits that are accurate to well under the sub-second level as evidenced by the 0.01-second accuracy around the time the Hartley 2 encounter. The EPOXI project plans to use this method to generate a complete and highly accurate set of UTC correlations for the flyby spacecraft since the launch, resulting in a future version of a SCLK kernel that will retroactively change correlation for **all** Deep Impact and EPOXI data. When this kernel is available, it will be added to the SPICE datasets for the two missions and posted on the NAIF/SPICE web site at http://naif.jpl.nasa.gov/naif/. The EPOXI project will provide more precise times for archived data as time and funding permit.   CCD Horizontal Gap ------------------ Calibration analysis combining Deep Impact and early EPOXI data determined the two halves of the MRI CCD - 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 raw FITS images. Since the values in these pixels vary dramatically, it is recommended that the values of the MINIMUM and 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.