Data Set Overview : This data set contains raw calibration and test images acquired by the Deep Impact Medium Resolution Instrument Visible CCD (MRI) during the cruise phase of the mission. These observations were used for optical and autonomous navigation (NAV) of the flyby spacecraft. These data were collected from 14 January to 25 April 2005. Test images of comet 9P/Tempel 1 were acquired on 25 April.  Software on board the flyby spacecraft used the optical navigation (OpNav) and autonomous navigation (AutoNav) images to compute the brightness centroid of the target body for trajectory corrections. Optical navigation was used for the cruise phase and most of the encounter phase, until two hours before impact when the AutoNav system took control of the flyby spacecraft in preparation for impact imaging. For more information about the AutoNav system, see Mastrodemos, et. al (2005) [MASTRODEMOSETAL2005].  A NAV observation consisted of one or more packets of data, each containing an 80-byte header plus a rectangle of image data called a ''snip'', cropped from a full-frame image. Pixels outside the snips were not returned. The Deep Impact Science Data Center (SDC) at Cornell University, used the packets for one observation to reconstruct a raw, full-frame image of 1008 by 1008 pixels. Pixels outside the snips were set to a value of zero with one common header. Locations of the snips within the frame were not captured by the data pipeline. Further details about these images are included in the processing section below.  Raw NAV images were grouped into daily directories by mid-observation date. A list of the NAV images in the data set is provided here:  Exposure IDs OBS Date DOY Minimum Maximum Observation Type ---------- --- ------- ------- ---------------------------------- 2005-01-14 014 1000000 1000004 Quick alignment 2005-01-15 015 1000006 1000010 Quick alignment 2005-01-26 026 1200001 1200080 AutoNav test 2005-01-30 030 1500000 1500004 Image snip test 2005-02-04 035 1500000 1500004 Image snip test 2005-02-06 037 1200004 1200560 AutoNav test 1300008 1300015 AutoNav test 2005-03-03 062 2100000 2100047 Attitude Determination and Control Subsystem (ADCS) alignment test 2005-04-01 091 2300000 2300184 OpNav Photometric calibration 2005-04-05 095 2010005 2010016 Focal length/Geometric distortion 2005-04-06 096 2030018 2030029 Focal length/Geometric distortion 2005-04-18 108 4200000 4200129 Nav engineering 2005-04-23 113 4200000 4200006 MRI-ADCS alignment 4200007 4200129 Stray light/Lookback attitude test 2005-04-25 115 4200000 4200029 MRI-ADCS alignment repeat; images include a snip of Tempel 1   Essential Reading ----------------- The following documents, located on the Deep Impact Documentation volume, DIDOC_0001, are essential for the understanding and interpretation of this data set:  NAV_IMAGES_REPORT.* : Description of how raw and reduced NAV FITS images were created for and processed by the Deep Impact science data pipeline NAV_MRI_RAW_CRUISE.* : Science-related image indices for this data set NAV_MRI_FILE_NAMES_RAW2CAL : Cross-reference of raw and reduced file names CALIBRATION_DOC.* : Instrument calibration by Klaasen, et al. (2006) [KLAASENETAL2006] INSTRUMENTS_HAMPTON.* : Instrument paper by Hampton, et al. (2005) [HAMPTONETAL2005] AUTO_NAVIGATION_MASTRODEMOS.* : Auto-navigation paper by Mastrodemos, et. al (2005) [MASTRODEMOSETAL2005] MISSION_OVERVIEW_AHEARN.* : Mission overview by A'Hearn, et al. (2005) [AHEARNETAL2005B] SCLK_CORRELATION.* : Discussion of the discrepancy between the spacecraft clocks and UTC AICD_FLIGHT_HRIV_MRI_ITS.* : Description of the data set and definitions of label keywords   Related Data Sets ----------------- The following PDS data sets are related to this one:  DIF-C-MRI-2-NAV-9P-ENCOUNTER-V1.0 : Raw MRI NAV encounter data DIF-C-MRI-3-NAV-9P-ENCOUNTER-V1.0 : Calibrated MRI NAV enctr data DI-C-SPICE-6-V1.0 : SPICE kernels  The related Deep Impact science data sets are:  DIF-CAL-MRI-2-9P-CRUISE-V1.0 : Raw MRI cruise data DIF-C-MRI-2-9P-ENCOUNTER-V1.0 : Raw MRI encounter data DIF-C-MRI-3/4-9P-ENCOUNTER-V2.0 : Calibrated MRI encounter data   Processing : The FITS images in this data set were created by the Deep Impact Science Data Center (SDC) at Cornell University and were assembled from raw NAV snips received from the flyby spacecraft. The NAV images report, listed above in the recommended reading section, discusses how the NAV data were processed into raw images. A summary is provided here.  NAV images were typically acquired during sequences designed to gather science data. The major difference between a science and NAV image was that a NAV observation was made of one or more packets of data, each containing an 80-byte header plus a rectangle of image data called a ''snip''. Because the snips were cropped from a full-frame image, not all pixels were returned in many cases. However, some images were returned in full as a single snip of 1008 by 1008 pixels.  Because one raw NAV observation was received as one or more snips, the SDC reconstructed a full frame of 1008 by 1008 pixels from the snips and stored the results as raw a FITS file. Since the raw NAV snips excluded the serial- and parallel-overclock pixels around the edges of the 1024 by 1024 array, these areas were not added to the reconstructed, raw frames. Also, pixels not returned were set to a value of zero in the raw FITS images.  Applied Coherent Technology Corporation in Herndon, VA, produced the PDS data labels by extracting parameters from the FITS headers.   Data :  File Naming Convention ---------------------- The naming convention for the data labels and FITS files was DxMeeeeeee_yyyydddhhmmssuuu.LBL or FIT, where:  D : Deep Impact x : Image usage (A for AutoNav or O for OpNav) M : MRI instrument eeeeeee : Exposure ID, same as for science data; image number within an exposure ID was always 1 of 1 yyyy : Ground-received time (GRT) year ddd : GRT day of year hhmmss : GRT hours, minutes, and seconds uuu : Suffix to provide uniqueness when two images were acquired or processed within the same second  Some images were downloaded more than once and processed by the SDC. For this case, each version of a raw image was included in this data set. For multiple downloads of one image, the exposure IDs in the file names are identical but the GRTs are different.   FITS CCD Images --------------- The two-dimensional, visible CCD images in this data set are in FITS format. The primary data array contains the CCD image. Each FITS file is accompanied by a detached PDS label. The document about NAV images provides a more detailed description of the image format.  Although a lossless compression algorithm was available, it was not used during flight. Therefore, all raw NAV FITS images in this data set are uncompressed (i.e., never compressed on board the spacecraft).   Target Name and Description --------------------------- The TARGET_NAME keyword in the data labels was set to the intended target, such as 'Calibration'. The TARGET_DESC keyword provides the name of the specific calibration target, such as 'NGC 3114'.   True-Sky ''As Seen By Observer'' Display ---------------------------------------- A true-sky 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 increasing to the top. This convention is also defined in the image labels:  SAMPLE_DISPLAY_DIRECTION : 'RIGHT' LINE_DISPLAY_DIRECTION : 'UP'  This topic is discussed in detail in the 'Quadrant Nomenclature' section of the 'Deep Impact Instrument Calibration' document.  The direction to Celestial North and Ecliptic North, measured clockwise from the top of the displayed image, is provided in PDS labels by CELESTIAL_NORTH_CLOCK_ANGLE and SOLAR_NORTH_POLE_CLOCK_ANGLE, both of which assume the correct display defined by SAMPLE_DISPLAY_DIRECTION and LINE_DISPLAY_DIRECTION.   Parameters :  Data Units ---------- Raw image data are in units of raw data numbers.   Imaging Modes and Filters ------------------------ The unbinned, full-frame, instrument mode 1 was always used for NAV images. Also, the only filters used were the two clear filters: 1 or 6, both centered at 650 nanometers. However, the exact filter was not known when the raw FITS images were created. Therefore, the filter-related keywords in the PDS labels are set to UNK (unknown). The exact filter was determined later during the pre-processing of raw NAV data for the calibration pipeline.  For descriptions of the imaging modes and filters, please see the Deep Impact instrument paper by Hampton, et al. (2005) [HAMPTONETAL2005].   Time-Related Keywords --------------------- All time-related keywords in the data labels, except EARTH_RECEIVED_TIME, are based on the clock on board the spacecraft. EARTH_RECEIVED_TIME provides the UTC when an Earth-based observer should be able to see an event recorded by the instrument.  Although the time to impact was not calculated for the NAV data, the estimated time of impact at the flyby spacecraft was UTC 05:44:34.265 on 4 Jul 2005. This is based on the conclusions presented in the spacecraft clock correlation report provided on the DI Documentation volume.   Geometry-Related Keywords ------------------------- The SOLAR_NORTH_POLE_CLOCK_ANGLE in the data labels specified the the direction of ecliptic north as projected onto the image plane. It is measured from the 'upward' direction, clockwise to the direction toward ecliptic north when the image is displayed as defined by the SAMPLE_DISPLAY_DIRECTION and LINE_DISPLAY_DIRECTION keywords.  The SDC pipeline was not able to automatically determine the proper geometric information for the target of choice in many cases. When these parameters could not be computed, the corresponding keywords in the PDS data labels were set to a value of unknown (UNK). Geometry-related keywords for most calibration targets were set to UNK.  Geometric parameters provided in the data labels were computed at the epoch specified by MID_IMAGE_TIME, except for the target-to-sun and earth-observer-to-target parameters. Target-to-sun values were calculated for the time when the light left the sun while earth-observer-to-target were calculated for the time when the light left the target.  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 discrepancy between the in-situ data and the ground- based observations. 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, please see the spacecraft clock correlation report provided on the DI documentation volume, DIDOC_0001.  The SPICE kernels used to calculated the geometric parameters are provided by the SPICE_FILE_NAME keyword in the PDS data labels. The kernels were listed in the order they were loaded into memory for processing.   Ancillary Data : Geometric parameters included in the data labels were computed using the DI SPICE data set archived in the PDS.   Coordinate System : Earth Mean Equator and Vernal Equinox of J2000 (EME J2000) was the inertial reference system used to specify observational geometry parameters in the data labels.

Confidence Level Overview : As noted above, the 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. For more information about this discrepancy, please see the spacecraft clock correlation document included on the Deep Impact document volume.  The FITS files in this data set were reviewed internally by the Deep Impact project and were used by the science team to calibrate the NAV images of 9P/Tempel 1.   Review : This data set was peer-reviewed in November 2006 and was accepted for the PDS archive pending resolution of liens (completed in June 2007).   Data Coverage and Quality : All expected data were received on the ground and are included in this data set. There are gaps in the exposure IDs in some daily data directories because NAV frames were interspersed with science frames.   Limitations :  1/3 Pixel Gap ------------- There is a 1/3-pixel, horizontal gap for a clocking phase between the upper and lower halves of the CCD. It was inserted by the manufacturer to facilitate the simultaneous upward and downward reading of the upper and lower quadrants. The gap causes a 10 percent reduction in the sensitivity of the two central rows (i.e., one row immediately above the gap and one below it).  Displaying Images ----------------- For some raw NAV images, there is little contrast between the snips and the surrounding ''missing'' pixels. To more easily view the snip(s) within a 1008x1008-pixel raw NAV FITS image, use a histogram equalization to scale the image for display.