PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = " 2004-08-25 S.McLaughlin Created; 2005-02-09 S.McLaughlin Resolved liens from Oct 2004 thermal-vac review; 2006-04-28 DI:S.McLaughlin Resolved liens from Apr 2006 peer review; 2006-12-07 DI:S.McLaughlin Resolved liens from Nov 2006 peer review; 2007-05-30 DI:S.McLaughlin Added RECORD_TYPE, reference id LINDLERETAL2007; 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 = "HRIV" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = " DEEP IMPACT HIGH RESOLUTION INSTRUMENT - VISIBLE CCD" INSTRUMENT_TYPE = "CCD CAMERA" INSTRUMENT_DESC = " Instrument Overview =================== The High Resolution Imager (HRI) consists of a long-focal-length telescope with a dichroic beam splitter located in front of the focal plane that reflected visible light (0.3 to 1.0 microns) through a filter wheel to a CCD for direct, optical imaging. The beam splitter transmits the near-infrared light (1 to 5 microns) to a 2-prism spectrometer. For convenience, we consider these as two separate instruments, HRIV (High Resolution Visible CCD) and HRII (High Resolution IR spectrometer), sharing the telescope since the two focal planes operate in parallel asynchronously. The HRI telescope is a classical Cassegrain design with the following parameters: The HRI telescope is a classical Cassegrain design with the following parameters: Primary aperture : 30.0 cm diameter, round Primary focal ratio : 4.5 Secondary Obscuration : 9.7 cm diameter, round Secondary magnification : 7.8x (net Cassegrain focal length 10.5 m) Back focal distance : 30.0 cm The dichroic beam-splitter has equal transmission and reflection occurring at about 1.05 microns. The filter wheel contains two clear apertures and seven filters. Five of the filters are roughly 100 nanometers in bandwidth, centered at 450, 550, 650, 750, and 850 nanometers. The shortest-wavelength filter is effectively a short-wavelength pass filter starting at 400 nanometers and limited to about 340 nanometers on the short end by the rapid decline in beamsplitter reflectivity. The longest wavelength filter is a long-pass filter starting at 900 nanometers that uses 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, with each quadrant read out through a separate amplifier. The electronics allows 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. Readout time for a full frame is 1.8 seconds. The HRIV instrument in full-frame 1024 x 1024 mode has the following field-of-view characteristics: Pixel Size : 21 micrometers Pixel FOV : 2.0 microradians or 0.41253 arcseconds Instrument FOV : 2.0 milliradians or 0.118 degrees Surface Scale : 1.4 meters/pixel at 700 kilometers The HRIV instrument includes an internal stimulator lamp for calibrating between the four quadrants of the CCD. The lamp is not a standard calibrator. One of its in-flight uses is to improve the photometry from the EPOXI exoplanet transit observations. The three instruments on the flyby spacecraft, HRIV, HRII (High- Resolution IR Imaging Spectrometer) and MRI (Medium-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 HRIV instrument is used for imaging 1) transits of known extrasolar planets, 2) Earth as a remotely-sensed planet, and 3) the encounter with comet 103P/Hartley 2. Instrument Calibration ====================== The HRIV instrument was originally calibrated by using in-flight data acquired during Deep Impact as well as pre-launch data taken during thermal-vacuum tests (TV2 and TV4) performed in 2002 and 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 HRIV 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 HRIV 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 HRIV instrument generally performed as expected during flight. However, images of stars acquired early in the Deep Impact mission indicated the HRI telescope was out of focus. An analysis showed the focus was forward of the CCD, so bakeouts were performed in late February and early March 2005 to improve the focus. The bakeouts reduced the defocus from 1.0 cm to 0.6 cm, which caused the width of star images to decrease from about 12 pixels to about 9 pixels. Star images continued to have a three-fold symmetry (six points) resulting from the three-point mounting of the primary and secondary mirrors. Most of the expected resolution can be regained by applying algorithms to deconvolve the HRIV images as described by Lindler, et al. (2007) [LINDLERETAL2007]. The EPOXI mission takes advantage of the poor focus characteristic which increases the point spread function of measurements, enabling high-precision photometry of known extrasolar planetary systems. For a detailed discussion about the focus of the HRI telescope, see Klaasen, et al. (2008) [KLAASENETAL2006] and Lindler, et al. (2007) [LINDLERETAL2007]. Calibration data acquired in 2008 for EPOXI show a 6% increase in the response of the HRIV 950-nm filter (#5) and changes to the electronic crosstalk between the CCD quadrants since 2005. Therefore new calibration constants for the 950-nm filter and 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 OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "LINDLERETAL2007" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END