Data Set Overview : This dataset contains calibrated clear-filter images of comet C/Garradd (2009 P1) acquired by the High Resolution Visible CCD (HRIV) from 20 February through 09 April 2012 during the Cruise 3 phase of the EPOXI mission.  While DI Flyby spacecraft (DIF) was officially in hibernation after the encounter with comet 103P/Hartley 2 in November 2010, it continued to carry out observations of comets from a distance as the opportunity arises. One such observing program was carried out in 2012 on comet C/Garradd (2009 P1). Observations were obtained with the HRIV CCD and the Medium Resolution Visible CCD (MRI, archived separately) during a series of windows from 20 February through 09 April 2012 as the comet receded from 1.74 AU to 2.11 AU from the Sun and at a distance of 1.88 AU to 1.30 AU from the spacecraft.  Hourly sequences were obtained between 20 February and 07 March and again between 06-09 April with a few gaps for spacecraft maneuvers and data downloads. During these windows, HRIV sequences consisted of a single Clear image, while each MRI sequence consisted of 13 broad- and narrowband images: 3 Clear, 3 CN, 2 C2, 2 OH and 2 Green Continuum. Images were unbinned 256x256-pixel subframe sections with the comet near the center of the frame.  Modified visible imaging sequences were interspersed with the 1.05- to 4.8-micron infrared spectral imaging scans (archived separately) obtained March 26-27 and April 2-3. During these windows, 3 HRIV Clear images were obtained every hour, while the MRI sequences consisted of 1 Clear and 1 CN image sampled every 15 minutes.  Initial results based on the visible-wavelength imaging are presented in Farnham, et al. (2014) [FARNHAMETAL2014]. See the 'Related Data Sets' section below for a list of separately archived visible- and infrared-wavelength data.  In the course of the observations of comet Garradd, a massive solar coronal ejection event occurred on 06 March 2012. The effects of this event were seen in the data obtained on 07 March, with cosmic rays rapidly increasing until they eventually overwhelmed the detector. This was the last day of the collection period, so the images had returned to normal by the next collection period on 25 March 2012.   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, 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].  INSTRUMENTS_HAMPTON.PDF - The Deep Impact instruments paper by Hampton, et al. (2005) [HAMPTONETAL2005] provides very detailed descriptions of the instruments.  HRIV_3_4_EPOXI_GARRADD.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:  DIF-C-HRIV-2-EPOXI-GARRADD-V1.0 - Raw HRIV high-resolution CCD images comet Garradd  DIF-C-MRI-2-EPOXI-GARRADD-V1.0 DIF-C-MRI-3/4-EPOXI-GARRADD-V1.0 - Raw and calibrated MRI medium-resolution CCD images comet Garradd, including context images for the IR scans  DIF-C-HRII-2-EPOXI-GARRADD-V1.0 DIF-C-HRII-3/4-EPOXI-GARRADD-V1.0 - Raw and calibrated HRII infrared spectral images of comet Garradd  DIF-C/E/X-SPICE-6-V1.0 - EPOXI SPICE kernels  DIF-CAL-HRII/HRIV/MRI-6-EPOXI-TEMPS-V3.0 - 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. N.B. The pipeline does not use these thermal data to calibrate IR spectra of the target. Instead it uses instrument temperatures recorded in the FITS headers.  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 data set were generated by the Deep Impact/EPOXI data pipeline, maintained by the project's Science Data Center (SDC) at Cornell University. The final version of the pipeline for HRIV processing, dated January 2013, was used. (This version is identical to the one used in June 2011 to process comet Hartley 2 data.) 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].  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 HRIV 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 (all images in this dataset were never compressed, so this step was bypassed) - 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 - The RAD stream has a potential step for deconvolving HRIV images to correct for the out-of-focus condition for the HRI telescope but this step was *not* performed  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.  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 raw data labels and FITS files is HVyymmddhh_eeeeeee_nnn_rr.LBL or FIT where 'HV' identifies the HRIV 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 6 frames were commanded for a scan with an exposure ID of 4010000, the first FITS file name would be HV12022019_4010000_001_RR.FIT and the last would be HV12022019_4010000_006_RR.FIT.   Image Compression ----------------- All data products in this dataset are uncompressed. Specifically all raw CCD images, from which these data products are derived, were never compressed on board the spacecraft.   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.  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 HRIV to the Medium Resolution Instrument Visible CCD (MRI) 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 ------------- One mode was used for all images in this dataset:  X-Size Y-Size Mode Name (pix) (pix) Comments ---- ------ ------ ------ ---------------------- 3 SF2S 256 256 Sub-frame, shuttered  For more information see Hampton, et al. (2005) [HAMPTONETAL2005], Klaasen, et al. (2008) [KLAASENETAL2006] and Klaasen, et al. (2013) [KLAASENETAL2011]. All modes are unbinned.   Filters ------- One HRIV filter was used for all images in this dataset:  Filter Center Width # Name (nm) (nm) Comments - ---------- ----- ----- ------------------------------- 1 CLEAR1 650 >700 Not band limited  For more information about the filters, see Hampton, et al. (2005) [HAMPTONETAL2005], Klaasen, et al. (2008) [KLAASENETAL2006] and Klaasen, et al. (2013) [KLAASENETAL2011]. For the effective center wavelengths and the corresponding full-width-half-max values see Klaasen, et al. (2013) [KLAASENETAL2011].   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.  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.  Since the pole of comet Garradd is not well known, the pipeline used the default SPICE kernel, GARRADD_0001.TPC, which specifies a non-rotating body with the positive pole aligned with EMEJ2000.   Ancillary Data : The timing and 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. Most kernels are available in the EPOXI SPICE dataset, DIF-C/E/X-SPICE-6-V1.0; others that had not yet been archived in the PDS when this dataset was produced are available online at the Operational Flight Project Kernels website maintained by the NASA Navigation and Ancillary Information Facility (NAIF), http://naif.jpl.nasa.gov/naif/data_operational.html.   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 dataset 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 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 EPOXI SIS document.   Limitations :  Timing ------ 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 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/.   HRI Telescope Focus ------------------- Images of stars acquired early during the Deep Impact mission in 2005 indicated the HRI telescope was out of focus. In-flight bakeouts during late February and early March 2005 reduced the defocus from about 1.0 cm to about 0.6 cm, resulting in a decrease in the width of stars from about 12 pixels to 9 pixels. For more detail, please see the Deep Impact instrument calibration paper by Klaasen, et al. (2008) [KLAASENETAL2006], the Deep Impact image restoration paper by Lindler, et al. (2007) [LINDLERETAL2007], and the EPOXI Comet Hartley 2 image restoration paper by Lindler, et al. (2013) [LINDLERETAL2013].  Please note the PSF files included in this dataset are the initial set produced by the science team for inclusion in the calibration pipeline; the PSFs are very non-circular due the focus problem, and the pixelization can lead to offsets of the center in one direction or another. Deconvolution with a PSF can be very difficult and one should fully understand the nature of the PSFs and the nature of the instrument before trying to use any PSF. For more information, see Barry, et al., (2010) [BARRYETAL2010], Lindler, et al. (2007) [LINDLERETAL2007], and Lindler, et al. (2013) [LINDLERETAL2013].  The HRIV images in this dataset were not deconvolved.   CCD Horizontal Gap ------------------ Calibration analysis combining Deep Impact and early EPOXI data determined the two halves of the HRIV 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 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.