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resolution for 23 Jul 2009 peer review. 2011-08-24 EPOXI:McLaughlin Resolved liens from the Aug 2011 peer review: fixed outdated wording; added reference KLAASENETAL2011. 2011-09-06 EPOXI:McLaughlin Added BELTONETAL2011 which discusses how the central horizontal gap was handled for aperture photometry of 9P/Tempel1. 2012-07-27 EPOXI:McLaughlin Improved description of apparent central horizontal 'gap' in the Instrument Calibration section. 2013-03-08 EPOXI:McLaughlin Resolved liens from Mar 2013 peer review: Added reference FARNHAMETAL2000; Changed pub date for KLAASENETAL2011;" OBJECT = INSTRUMENT INSTRUMENT_ID = "MRI" INSTRUMENT_HOST_ID = "DIF" 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; see Farnham, et al. (2000) [FARNHAMETAL2000]. 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 continued through the EPOXI mission to monitor performance and to provide additional data for refining the calibration pipeline. Instrument calibration for Deep Impact is discussed by Klaasen, et al. (2008) [KLAASENETAL2006]; instrument calibration for EPOXI is discussed by Klaasen, et al. (2013) [KLAASENETAL2011]. The two central rows of the CCD are physically 1/6-pixel narrower and collect only 5/6 of the charge of a normal row (Klaasen, et al., 2008 [KLAASENETAL2006]; Klaasen, et al., 2013 [KLAASENETAL2011]). However, the data pipeline reconstructs images with uniform row spacing, which introduces a 1/3-pixel extension at the center of the raw and calibrated image arrays. Thus for two features on either side of the midpoint line outside of the two central rows, the vertical component of the true angular separation between those features is one-third of a pixel less than their measured separation in the reconstructed image. As for all geometric distortions, correction of this 1/3-pixel extension will require resampling of the image and an attendant loss in spatial resolution. The data pipeline process does not perform this correction in order to preserve the best spatial resolution. However, it does correct for the 1/6 decrease of signal in the two central rows by the flat-field division so that the pixels in those two rows have the correct scene radiance in the calibrated images. Thus, the surface brightness measurement is preserved anywhere in the geometrically distorted but calibrated images. Point source or disk-integrated photometric measurements using aperture photometry that includes these central rows will be slightly distorted unless special adjustments are made, such as subtracting 1/6-pixel worth of signal to the two central rows and adjusting for the geometric distortion in the calibrated images, as described in Appendix A of Belton, et al. (2011) [BELTONETAL2011]. An alternative method that corrects for the 1/3-pixel extension was developed for Hartley 2 photometry and is described in the dataset DIF-C-MRI-5-EPOXI-HARTLEY2-PHOTOM-V1.0. Flight Performance ================== The MRI instrument generally performed as expected during flight. Calibration data acquired throughout EPOXI showed changes to the flat fields, the electronic crosstalk between the CCD quadrants, the response of the filters, and the calibration constants since Deep Impact in 2005. Therefore new calibration files and constants were incorporated into the calibration pipeline for EPOXI processing; additional improvements such as stripe removal are discussed by Klaasen, et al. (2013) [KLAASENETAL2011]. This instrument description was originally provided by Dr. Michael A'Hearn for the Deep Impact mission, then updated as the EPOXI mission progressed." END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "BELTONETAL2011" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "KLAASENETAL2011" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "FARNHAMETAL2000" 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 = "HAMPTONETAL2005" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "KLAASENETAL2006" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END