Data Set Overview : This dataset contains calibrated, 1.05- to 4.8-micron spectral images of comet C/Garradd (2009 P1) acquired by the High Resolution Infrared Spectrometer on 26 March and 02-03 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). The infrared spectra were obtained in two separate observing sequences in the observing window (set by solar elongation as seen from the spacecraft) on 26 March and 02-03 April 2012, when the comet was at approximately 2 AU from the sun outbound and 1.4 AU from the spacecraft and at a phase angle of about 35 degrees. All observations consisted of spatial scans perpendicular to the length of the slit (in order to ensure that the comet was imaged, allowing for pointing uncertainties) consisting of 17 frames, obtained at a scan rate of 2 slit-widths per frame with an integration time of 12 seconds per frame. Each frame is a single, long-slit spectrum averaging over an effective area of 10x20 microradians. Each sequence consisted of 64 scans, of 17 binned full frames (512x256-pixels) each. The scans were taken at 15-minute intervals, beginning at approximately 07:34 UTC on 26 March 2012 and 08:19 UTC on 02 April 2012. Visible-wavelength imaging was also obtained for context information during these observing sessions, but those data are archived with all the other Visible-wavelength imaging data. Initial results based on these spectral data, including a detailed description of the scanning technique, are presented in Feaga, et al. (2014) [FEAGAETAL2014].  Visible-wavelength imaging was also obtained for context information during these observing sessions, but those data are archived with all the other visible-wavelength observations. See the 'Related Data Sets' section below.   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.  HRII_3_4_EPOXI_GARRADD.TAB - This ASCII table provides image parameters such as the mid-obs Julian date, exposure time, image mode, 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.  HRII_GARRADD_DATA_ARTIFACT.ASC - This ASCII report briefly describes an artifact found in the comet Garradd IR spectra on DOY 093, 2 April 2012, due to burst noise on the sensor.   Related Data Sets ----------------- The following PDS datasets are related to this one and may be useful for research:  DIF-C-HRII-2-EPOXI-GARRADD-V1.0 - Raw HRII infrared spectral images of comet Garradd  DIF-C-HRIV-2-EPOXI-GARRADD-V1.0 DIF-C-HRIV-3/4-EPOXI-GARRADD-V1.0 - Raw and calibrated 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/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 (wavelength and spatial/along-slit) FITS spectral images and PDS labels in this dataset were generated by the Deep Impact/EPOXI calibration pipeline, maintained by the project's Science Data Center (SDC) at Cornell University. The final version of the pipeline for HRII processing, dated January 2013, was used. 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 HRII spectra, 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.  - 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.  The calibration pipeline performed the following processes, in the order listed, on the raw HRII FITS data to produce the RADREV and RAD products found in this dataset (the pipeline uses the image mode to select the appropriate set of calibration files):  - Calibration of temperatures and voltages in the FITS header - Per-pixel linearization of raw data numbers - Subtraction of dark noise, derived for per-pixel linearization (the prisms/spectral imaging module and IR focal plane array temperatures, OPTBENT and IRFPAT in the FITS header, are used for scaling if dark modeling is required) - Division by a flat field, derived for per-pixel linearization - Determine spectral registration and bandwidth for each pixel (using OPTBENT from FITS headers) - Conversion of data numbers to units of radiance for an absolute, radiometric calibration that is reversible (RADREV) and that was derived for per-quadrant linearization - 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. - Set non-image pixels at the left, right, and bottom edges to zero in the RADREV and RAD products. The 'real data' window of an image is given by CALWINDW in the FITS header. If edge pixels need to be analyzed, the original DN values can be found in the raw products located in the PDS dataset, DIF-C-HRII-2-EPOXI-GARRADD-V1.0.  As part of the calibration process, the pipeline updated the per-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 derived for per-pixel linearity (missing pixels were identified when the raw FITS files were created).  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, which are briefly described in the next section. 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 spectral image is stored as FITS. The primary data unit contains the two-dimensional spectral image, with the fastest varying axis corresponding to increasing wavelengths from about 1.05 to 4.8 microns and the slowest varying axis corresponding to the spatial or along-slit dimension. The primary image is followed by four image extensions that are two-dimensional pixel-by-pixel maps providing additional information about the spectral 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 the spectral registration or wavelength for each pixel in the primary image. This extension is required because the wavelength for each pixel changes as the temperature of the instrument increased or decreased.  - The third extension provides the spectral bandwidth for each pixel in the primary image. This extension is required because the bandwidth for each pixel changes as the temperature of the instrument increased or decreased.  - The fourth extension provides a signal-to-noise ratio for each pixel in the primary image.  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 calibrated data labels and FITS files is HIyymmddhh_eeeeeee_nnn_rr.LBL or FIT where 'HI' identifies the HRII 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 can be commanded for one exposure ID. For a spectral scan, many frames are acquired 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 17 frames were commanded for a scan with an exposure ID of 4000001, the first FITS file name would be HI12032607_4000001_001_RR.FIT and the last would be HI12032607_4000001_017_RR.FIT.   Image Compression ----------------- All data products in this dataset are uncompressed. Specifically all raw spectral 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.   Spectral Scans -------------- Each HRII scan in this dataset consists of multiple frames within one exposure ID (OBSERVATION_ID in the data labels). To work with these 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.   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 Visible CCD (MRI) and the High Resolution Instrument Visible CCD (HRIV), see the instrument alignment section of the EPOXI SIS document or Klaasen, et al. (2013) [KLAASENETAL2011].  In many cases, nearly simultaneous MRI images, located in the dataset DIF-C-MRI-3/4-EPOXI-GARRADD-V1.0, were acquired with each IR scan and should provide field of view context for the slit location.   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 is reset and read out on a pixel-by-pixel basis, the read out order affects the time at which each pixel is exposed although each pixel has the same exposure duration -- except for the ALTFF mode that has different read and reset causing the effective exposure time to vary with line number, i.e., along the slit in the spatial direction. Additionally, the end of the spectrometer slit that always points roughly towards the sun is the first line to be readout and the last line to be read out is furthest from the sun, assuming the spacecraft is in its usual orientation with the solar panels pointing roughly toward the sun. For more information about the timing of the spectra, see the zero exposure background section of the EPOXI instrument calibration paper by Klaasen, et al. (2013) [KLAASENETAL2011].   Parameters :  Data Units ---------- The calibrated RADREV and RAD spectral 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 Bin Mode Name (pix) (pix) Type Comments ---- ------ ------ ----- ----- ------------------- 1 BINFF 512 256 2x2 Binned full frame  In the table above, X-Size is the spectral dimension and Y-Size is the spatial dimension along the slit. For more information see Hampton, et al. (2005) [HAMPTONETAL2005], Klaasen, et al. (2008) [KLAASENETAL2006] and 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. Additionally, any missing pixels in a frame (within an exposure ID) that is used as the in-scene dark will contaminate the calibrated observations of the same exposure ID, and those contaminated pixels will not be identified as missing in the image quality map extension but will appear as horizontal stripes in the calibrated spectra.  Transient anomalous pixels may be present in the data.   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. However, this focus problem does not significantly affect the HRII instrument. For more details please see the Deep Impact instrument calibration paper by Klaasen, et al. (2008) [KLAASENETAL2006].   Displaying Images ----------------- Flight software writes an image header over the first 100 bytes of quadrant A. These image header pixels are 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 reference rows and columns located at the edges of the image. For more information, see the quadrant nomenclature section of the EPOXI SIS document.