PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = " 2004-08-25 S.McLaughlin Created; 2005-02-10 S.McLaughlin Resolved liens from Oct 2004 thermal-vac review; 2006-05-18 DI:S.McLaughlin Resolved liens from Apr 2006 peer review; 2006-10-02 DI:S.McLaughlin Corrected FOV characteristics; 2006-12-07 DI:S.McLaughlin Resolved liens from Nov 2006 peer review; 2007-05-30 DI:S.McLaughlin Added reference id KLAASENETAL2005; 2009-01-02 EPOXI:McLaughlin Updated for EPOXI mission; 2009-01-20 EPOXI:McLaughlin Revised explanation about decreased sensitivity at horizontal quadrant boundary; 2009-05-22 EPOXI:McLaughlin Additional updates for EPOXI. 2009-09-11 EPOXI:McLaughlin Lien resolution for 23 Jul 2009 peer review. " OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = "DIF" INSTRUMENT_ID = "MRI" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = " DEEP IMPACT MEDIUM RESOLUTION INSTRUMENT - VISIBLE CCD" INSTRUMENT_TYPE = "CCD CAMERA" INSTRUMENT_DESC = " Instrument Overview =================== The Medium Resolution Imager consists of an f/17.5 Cassegrain telescope followed by a filter wheel feeding directly onto a CCD for direct, optical imaging. The MRI telescope is a classical Cassegrain design with the following parameters: Primary aperture : 12.0 cm diameter, round Primary focal ratio : 3.75 Secondary Obscuration : 6.6 cm diameter, round Secondary magnification : 4.75x (net Cassegrain focal length 210 cm) Back focal distance : 30.0 cm The filter wheel contains two clear apertures and eight filters. The filters include duplicates of some of the medium-band filters in the High Resolution Instrument and narrow-band filters that isolate OH, CN, and C2 as well as the green and violet continuum. These narrow-band filters were designed to match the Hale-Bopp filter sets used for ground-based programs since 1996. The longest wavelength filter is actually a long-pass filter that used the CCD response to define the long-wavelength cutoff at about 960 nanometers. Filter transmission profiles are illustrated by Hampton, et al. (2005) [HAMPTONETAL2005] and provided in the calibrated science data sets for the Deep Impact and EPOXI missions. The detector is a 1024 x 1024 split-frame, frame-transfer CCD with 21-micron-square pixels. The electronics allow readout of centered sub-frames in multiples of 2: 64x64, 128x128, and so on, with or without rows of overscan. Transfer time, to move the two halves of the image from the exposing area to the two shielded areas, is about 5.2 milliseconds. There are readout amplifiers in each of the four quadrants. Readout time for a full frame is 1.8 seconds. Net pixel scale is 10 microradians/pixel (2 arcseconds/pixel). The MRI instrument in full-frame 1024 x 1024 mode has the following field-of-view characteristics: Pixel Size : 21 micrometers Pixel FOV : 10.0 microradians or 2.06265 arcseconds Instrument FOV : 10.0 milliradians or 0.587 degrees Surface Scale : 7 meters/pixel at 700 kilometers The MRI instrument includes an internal stimulator lamp for calibrating between the four quadrants of the CCD; it is not a standard calibrator. The three instruments on the flyby spacecraft, MRI, HRII (High Resolution IR Imaging Spectrometer) and HRIV (High Resolution Visible CCD), are mounted on a separate instrument platform together with the star trackers. The three instruments are nominally co-aligned as described by Klaasen, et al. (2008) [KLAASENETAL2006]. For a detailed discussion of the instrument and how it was used during the Deep Impact mission, see Hampton, et al. (2005) [HAMPTONETAL2005] and Klaasen, et al. (2005) [KLAASENETAL2005]. For the EPOXI mission, the MRI instrument is used primarily during the encounter with comet 103P/Hartley 2. Instrument Calibration ====================== The MRI instrument was originally calibrated by using in-flight data acquired during Deep Impact as well as pre-launch data taken during a thermal-vacuum test (TV4) performed in 2003. In-flight calibrations continue through the EPOXI mission to monitor performance and to provide additional data for refining the data calibration pipeline. Instrument calibration as well as the pipeline that is shared by Deep Impact and EPOXI is discussed by Klaasen, et al. (2008) [KLAASENETAL2006]. 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. Flight Performance ================== The MRI instrument generally performed as expected during flight. However calibration data acquired in 2008 for EPOXI show changes to the electronic crosstalk between the CCD quadrants since 2005. Therefore new crosstalk coefficients were calculated and incorporated into the calibration pipeline for EPOXI processing. This instrument description was originally provided by Dr. Michael A'Hearn for the Deep Impact mission and will be updated as the EPOXI mission progresses. " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "HAMPTONETAL2005" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "KLAASENETAL2005" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "KLAASENETAL2006" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END