Data Set Overview : This data set set contains version 1.0 of calibrated 750-nm filter images of Earth acquired by the Deep Impact Medium Resolution Visible CCD during the EPOCh phase of the EPOXI mission. The MRI instrument was only used during first Earth observing period on 18-19 March 2008. The observing period lasted approximately 24 hours, and one MRI image was taken simultaneously with the first north/south scan of the HRI IR spectrometer at half-hour intervals. These MRI data serve as context images for the IR spectral scans. Additional Earth observations are planned for the mission, and, if acquired, MRI images will be added to a future version of this data set.   Required Reading --------------- The following documents are essential for the understanding and interpretation of this data set. Please note the most recent version of these documents, including other formats such as ASCII text, can be found in the Deep Impact and EPOXI documentation data set, DI-C-HRII-HRIV-MRI-ITS-6-DOC-SET-V2.0.  EPOXI_SIS.PDF - The Archive Volume and Data Product Software Interface Specifications document (SIS) describes the the data set, the science data products, and defines keywords in the PDS labels.  CALIBRATION_PAPER_DRAFT.PDF - The Deep Impact instrument calibration paper by Klaasen, et al. (2008) [KLAASENETAL2006] describes how the instruments were calibrated for Deep Impact and similarly for EPOXI and explains the calibration process used for both missions. The published version should be available online in the Review of Scientific Instruments by the American Institute of Physics. The EPOXI archive provides only an incomplete draft.  INSTRUMENTS_HAMPTON.PDF - The Deep Impact instruments paper by Hampton, et al. (2005) [HAMPTONETAL2005] provides very detailed descriptions of the instruments.  EPOCH_EARTH_OBS.PDF - This document describes of the EPOCh Earth observations although most of the information is captured in this data set catalog file you are reading.  EPOCH_EARTH_SEQ_2008.PDF - This document provides pointing and sequencing information for the EPOCh Earth observations in 2008, including descriptions of the HRII scans of Earth (scan direction, rate, etc.).  EPOCH_OVERVIEW.PDF - This presentation provides an overview of the EPOCh phase of the EPOXI mission.  MRI_3_4_EPOXI_EARTH.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 data set. This file is very useful for determining which data files to work with.  Publications of the scientific results from the Earth observations in this data set include Cowan, et al. (2009) [COWANETAL2009] and Livengood, et al. (2009) [LIVENGOODETAL2009].   Related Data Sets ----------------- The following PDS data sets are related to this one and may be useful for research:  DIF-E-MRI-2-EPOXI-EARTH-V1.0 - Raw MRI Earth observations (context images)  DIF-E-HRII-2-EPOXI-EARTH-V1.0 DIF-E-HRII-3/4-EPOXI-EARTH-V1.0 - Raw and calibrated 1.05- to 4.8-micron HRI IR spectra of Earth, covering the same observing period as this data set  DIF-E-HRIV-2-EPOXI-EARTH-V1.0 DIF-E-HRIV-3/4-EPOXI-EARTH-V1.0 - Raw and calibrated HRIV visible CCD Earth observations at 350, 450, 550, 650, 750, 850, and 950 microns, covering the same three observing periods as this data set  DI-C-HRII-HRIV-MRI-ITS-6-DOC-SET-V2.0 - Deep Impact and EPOXI documentation set  DIF-C/E/X-SPICE-6-V1.0 - EPOXI SPICE kernels  DIF-CAL-HRII/HRIV/MRI-6-EPOXI-TEMPS-V1.0 - 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   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. 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).  The calibration pipeline performed the following processes on the raw MRI FITS data to produce the RADREV and RAD products found in this data set:  - Decompression of compressed images (Earth images were not compressed) - Correction for bias - Subtraction of a dark frame - 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 for a signal-to-noise ratio map. The calibration steps and files applied to each raw image are listed in the PROCESSING_HISTORY_TEXT keyword in the PDS data label. For a detailed discussion of the calibration pipeline and the resulting data, see the Deep Impact instrument calibration document and the EPOXI SIS document.   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.  For more information about the FITS primary image and the extensions, refer to the Deep Impact instrument calibration document or the EPOXI SIS document  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.   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 32 frames were commanded for a scan with an exposure ID of 1000000, the first FITS file name would be MV08031818_1000000_001_RR.FIT and the last would be MV08031818_1000000_032_RR.FIT.   Image Compression ----------------- All data products in this data set are uncompressed. If the associated raw data products was compressed on board the flyby spacecraft (and thus received on the ground and archived as compressed) then the calibration pipeline uses one of four 8-bit lookup tables to decompress the raw image. However, the Earth images acquired acquired during the time period covered by this data set were never compressed. For more information about this topic, see the image compression section of the Deep Impact instrument calibration documents.   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) increasing to the right in the display window and the slowest-varying axis (lines) 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 Deep Impact instrument calibration document. Also the EPOXI SIS has a brief discussion of this topic.   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 relative boresight alignments section of the Deep Impact instrument calibration document.   Parameters :  Data Units ---------- The calibrated RADREV and RAD image data have units of radiance, W/(m**2 steradian micron).   Imaging Modes ------------- One MRI image mode was used for all Earth observations:  X-Size Y-Size Mode Name (pix) (pix) Comments ---- ------ ------ ------ --------------------------------------- 2 SF1 512 512 Sub-frame, shuttered  All modes are unbinned. For a thorough description of the imaging modes, please see the Deep Impact instruments document or the Deep Impact instrument calibration document. Also the EPOXI SIS has a brief discussion of this topic.  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 ------- One MRI filter was used for all Earth observations:  Filter Center Width # Name (nm) (nm) Comments - ---------- ----- ----- ------------------------------- 4 RED 750 100 For context  For more information about the filters, see the Deep Impact instruments document or the Deep Impact instrument calibration document. Also the EPOXI SIS has a brief discussion of this topic.   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.  For Earth observations, sub-spacecraft and sub-solar longitude and latitude coordinates (planetocentric, body-fixed rotating) are provided, when available, in the data labels by SUB_SPACECRAFT_LONGITUDE, SUB_SPACECRAFT_LATITUDE, SUB_SOLAR_LONGITUDE, and SUB_SOLAR_LATITUDE.  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 that were calculated for the time when the light arrived at the target and the earth-observer-to-target values that were calculated for the time when the light left the target.  The flyby spacecraft clock SPICE kernels (SCLK) used to convert to UTC and to calculate geometry-related parameters for this data set have a known accuracy of no better than 0.5 seconds. However as this data set was being produced, the mission operations team figured out how to correct raw clock correlation data for the flyby spacecraft to allow timing fits that are accurate to at least the sub-second level. The project plans to generate a complete, corrected set of 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 data sets for the two missions and posted on the NAIF/SPICE web site at http://naif.jpl.nasa.gov/naif/.   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. NAIF used these kernels to produce the EPOXI SPICE data set, 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, unless specified otherwise (e.g, SUB_SPACECRAFT_LONGITUDE).   Software : The observations in this data set 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 data set.

Confidence Level Overview : The data files in this data set were reviewed internally by the EPOXI project.   Review : This data set is archived at the PDS Small Bodies Node (SBN) and the Multi-Mission Archive at STScI (MAST). It passed a peer review held by SBN on 23 July 2009; MAST personnel participated.   Data Coverage and Quality : There are no unexpected gaps in this data set. All Earth observations received on the ground were processed 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 EPOXI SIS document.   Limitations :  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 biased during integration so that the centers of the two halves are apparently 1/6 pixel closer to the center, and the two boundary rows show a decrease in sensitivity of 1/6. Reconstructed image files space all lines evenly, so the true image is erroneously vertically pushed apart by 1/3 pixel at its center in these reconstructions. When making science measurements from MRI images, one must therefore be very careful to properly account for the two flaws introduced by the apparently narrow central lines on the CCD - a geometric error that separates the image by an extra 1/3 pixel at the horizontal quadrant boundary, and 2) insertion of extra total radiance into calibrated images due to the flat-field correction, which corrects for an apparent radiance deficit in the two central rows because of the smaller number of photons actually incident on those rows.   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 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 Deep Impact instrument calibration document or the EPOXI SIS document.