Data Set Overview : This data set contains photometric measurements of comet 9P/Tempel 1 from images taken with the Medium Resolution CCD Instrument during the approach phase of the Deep Impact mission (from 1 May 2005 to 4 July 2005). These data, based on circular apertures ranging from 5 to 30 pixels in diameter, were derived from both science and navigation images taken through clear filters.   Observations ------------ These tables consist of measurements performed on images taken from 1 May 2005 to about six hours before impact, defined here as 05:44:34.265 UT 4 July 2005 at the flyby spacecraft. All dates provided in the tables refer to the mid-point of the observation. The heliocentric distance of 9P/Tempel 1 goes from 1.64 AU to 1.51 AU during approach. A total of 3014 images were analyzed: 595 science images and 2419 optical navigation images.   Related Data Sets ----------------- The following PDS data sets were used to derive these data:  DIF-C-MRI-3/4-9P-ENCOUNTER-V2.0/DATA/RADREV : Calibrated, radiance MRI encounter data, version 2.0 DIF-C-MRI-2-NAV-9P-ENCOUNTER-V1.0 : Raw MRI navigation data  Please note that MRI reversibly calibrated, radiance (RADREV) science images were used in this analysis. These data were not processed to remove artifacts, such as cosmic rays, which sometimes affect the tabulated results. Also, measurements derived from navigation images were acquired from the raw data.   Data :  Tables of Photometric Data -------------------------- The nav_phot.tab and sci_phot.tab files are fixed-width, ASCII tables that contain photometric measurements of comet 9P/Tempel 1 taken with 5, 7, 9, 15, 20, 25, and 30 pixel diameter apertures. Observation dates are included in the tables, as is the centroid position of the comet in the image. These files additionally contain a column specifying the filter used to take the image and another column listing the centroid's distance from the horizontal boundary between the CCD quadrants. For more information about the MRI CCD instrument and its filters, Deep Impact instruments publication by Hampton, et al. (2005) [HAMPTONETAL2005] provided in the Deep Impact documentation data set, DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V1.0, which is archived by the PDS.   Processing : The following assumes that the images are displayed with lines increasing up and samples to the right.   Science Data ------------ Photometric measurements were derived from the reversibly calibrated RADREV images taken through the MRI clear filters. An additional background subtraction algorithm was applied to these data in order to remove the horizontal ''striping'' caused by electrical interference. This noise, whose amplitude is on the order of a few DN, most adversely affects the data taken early on in the approach sequence.  In many of these images, the comet was located on or close to the boundary between the upper and lower halves of the CCD. The pixels in the rows surrounding this boundary are 1/6 of a pixel smaller than the other pixels of the CCD. This increases the point spread function of objects that overlap this boundary by 1/3 of a pixel. Flux measurements similarly tend to be greater at the boundary. In about 80 percent of the images, the comet centroid lies less than 20 pixels away from this boundary. For a more detailed discussion of how this affects the data and what corrections were applied, please see the Deep Impact MRI photometry report included in the document directory of this data set.  For more information about how the RADREV science data were calibrated, see the Deep Impact (Science) Calibration Pipeline Summary included in the document directory of the data set or the Deep Impact instrument calibration report by Klaasen, et al. (2006) [KLAASENETAL2006] included in the Deep Impact documentation data set, DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V1.0, which is archived by the PDS.   Optical Navigation Data ----------------------- An optical navigation image consists of a number of ''snippets'', each containing an object of interest to the navigation team (for example, a guide star). Comet 9P/Tempel 1 is always contained in one of these ''snippets'', which varied in size from 350x350 pixels for most of the approach sequence to 150x150 pixels for the last week before impact. These images do not have serial and parallel overclock pixels and therefore needed to be treated differently from the science images. Only the raw navigation images are used in this analysis.  A background subtraction procedure was applied only to the snippet containing the comet. This procedure also removed the horizontal striping previously discussed for all images taken more than one week before impact. In data taken between UTC 2005-06-27T05:44:09.225 and impact, the comet's coma fills the snippet, which could therefore not be used to remove the background. For this time frame, the background was measured in the relevant image quadrant from a raw science image taken close in time to the navigation image of interest.  For a detailed description of the navigation data, please see the Deep Impact navigation images report included in the document directory of this data set. For additional information on the reduction processes applied to these data, please see the Deep Impact MRI photometry report included in the document directory of this data set.   This data set overview was provided by F. Bastien. For a detailed discussion of this data set, please refer to the Deep Impact MRI photometry report included in the document directory of this data set.

Limitations : The following assumes that the images are displayed with lines increasing up and samples to the right.   Navigation Images ----------------- These data excluded the serial and parallel overclock pixels. Therefore, quadrant bias and background was determined from the edge of the snippet of interest for most of approach. For more information about how the raw navigation images were processed, please see the Deep Impact navigation images report included in the document directory of this data set.   ''Striping'' ------------ All the data were affected by a horizontal striping of a few DN in amplitude caused by electrical interference. This primarily affected the early approach images.   CCD Horizontal Gap ------------------ The pixels in the two rows surrounding the horizontal boundary between the upper and lower halves of the CCD are each 1/6 of a pixel smaller than the other pixels of the CCD. This increases the point spread function of objects that overlap this boundary by 1/3 of a pixel. Flux measurements similarly tend to be greater at the boundary.   For more on how these limitations were dealt with, see the Deep Impact MRI photometry report included in the document directory of this data set.   Review : This data set was peer-reviewed in June 2008 and was approved for archiving pending resolution of liens. Liens were resolved in January 2009.