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 " 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 = " The instrument overview was provided by Dr. Michael A'Hearn, the principal investigator for the Deep Impact mission. For a detailed discussion of the instrument, see Hampton, et al. (2005) [HAMPTONETAL2005]. Instrument Overview =================== The High Resolution Imager (HRI) consisted of a long-focal-length telescope with a dichroic beam splitter, located in front of the focal plane, that reflected visible (0.3 to 1.0 microns) light through a filter wheel to a CCD for direct, optical imaging. The beam splitter transmitted the near-infrared light (1 to 5 microns) to a 2-prism spectrometer. For convenience, we considered these as two separate instruments, HRIV and HRII, sharing the telescope since the two focal planes operate in parallel asynchronously. The HRI telescope was 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 had equal transmission and reflection occurring at about 1.05 microns. The filter wheel contained two clear apertures and 7 filters. Five of the filters were roughly 100 nanometers in bandwidth, centered at 450, 550, 650, 750, and 850 nanometers. The shortest-wavelength filter was 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 was a long-pass filter starting at 900 nanometers that used the CCD response to define the long-wavelength cutoff at about 960 nanometers. The detector was a 1024 x 1024 split frame-transfer CCD with 21-micron-square pixels, with each quadrant read out through a separate amplifier. The electronics allowed 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, was about 5.2 milliseconds. Readout time for a full frame was 1.8 seconds. The HRIV instrument in full-frame 1024 x 1024 mode had the following field-of-view characteristics: Pixel Size : 21 micrometers Pixel FOV : 2.0 microradians Instrument FOV : 2.0 milliradians or 0.118 degrees Surface Scale : 1.4 meters/pixel at 700 kilometers The three instruments on the flyby spacecraft, HRII, HRIV and MRI, were mounted on a separate instrument platform together with the star trackers. The three instruments were nominally co-aligned. For a detailed discussion of the instrument, see Hampton, et al. (2005) [HAMPTONETAL2005]. This instrument overview was provided by Dr. Michael A'Hearn, the principal investigator for the Deep Impact mission. Instrument Calibration ====================== The HRIV instrument was calibrated by using in-flight data as well as pre-launch data taken during thermal-vacuum tests (TV2 and TV4) performed in 2002 and 2003. The calibration of the HRIV instrument was discussed in the 'Deep Impact Instrument Calibration' paper by Klaasen, et al. (2006) [KLAASENETAL2006]. Flight Performance ================== The HRIV instrument generally performed as expected during flight. However, early images of stars 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. For a detailed discussion about the focus of the HRI telescope, please see the 'Deep Impact Instrument Calibration' paper by Klaasen, et al. (2006) [KLAASENETAL2006]. " END_OBJECT = INSTRUMENT_INFORMATION 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