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. 2010-03-08 EPOXI:McLaughlin Added reference for BARRYETAL2010 (EPOXI PSFs). 2011-08-24 EPOXI:McLaughlin Resolved liens from the Aug 2011 peer review: fixed outdated/redudant wording; added reference KLAASENETAL2011. 2011-09-06 EPOXI:McLaughlin Added BELTONETAL2011 which discusses how the central horizontal gap was handled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. 2012-12-12 EPOXI:McLaughlin 12-12-12! Added reference LINDLERETAL2012. 2013-03-08 EPOXI:McLaughlin Resolved liens from Mar 2013 peer review: Fixed minor typos; Changed pub date for KLAASENETAL2011; Changed LINDLERETAL2012 to LINDLERETAL2013." OBJECT = INSTRUMENT INSTRUMENT_ID = "HRIV" INSTRUMENT_HOST_ID = "DIF" 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 reflects 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: 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 HRII instrument imaged transits of known extrasolar planets, Earth and Mars as remotely-sensed planets, and 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 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 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] and Lindler, et al. (2013) [LINDLERETAL2013]. 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]. During the EPOXI mission, new target-specific point spread functions (PSFs) were produced from data acquired in 2008 of exoplanet transit targets such as GJ 436 and stellar calibrators such as Canopus. See Barry, et al., (2010) [BARRYETAL2010] for more information. These PSFs are archived as a data set in the PDS: DIF-CAL-HRIV-6-EPOXI-STELLAR-PSFS-V1.0. Calibration data acquired throughout EPOXI showed changes to the flat fields, the electronic crosstalk between the CCD quadrants, and the response of the filters 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 = "LINDLERETAL2013" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "LINDLERETAL2007" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "BARRYETAL2010" END_OBJECT = INSTRUMENT_REFERENCE_INFO 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 = "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