Data Set Overview
    =================
      This data set contains raw and reduced mid-infrared images and
      photometry of comet 9P/Tempel 1, the target of the Deep Impact
      mission.  Images were acquired on the night of 21 August 2000, about
      7.5 months after perihelion, by Y. Fernandez, C. Lisse, M. A'Hearn
      and M. Belton using the Long Wavelength Spectrometer instrument at
      the Keck I telescope.
 
      Observations were made with filters centered at 4.8, 8.0, 8.9, 10.7,
      11.7, 12.5, 17.9 and 20.0 microns.  The calibration procedure and
      photometric results are described in detail in the paper 'The nuleus
      of 'Deep Impact target Comet 9P/Tempel 1' by Fernandez et al. 2003
      [FERNANDEZETAL2003].
 
      This data set supports analysis of the size and albedo of the nucleus
      of 9P/Tempel 1 for the Deep Impact mission.
 
 
    Parameters
    ==========
      The plate scale was 0.080 arcsecond/pixel, yielding a 10.24-arcsecond
      field of view.  Other observational parameters for each image, such
      as filter name, are incorporated into the PDS labels and FITS headers
      supplied with the data.
 
      STOP_TIME in the PDS data labels is not supplied because the values
      for START_TIME and EXPOSURE_DURATION cannot be added to calculate the
      stop time for one observation.  For LWS data, EXPOSURE_DURATION,
      equivalent to OBJTIME in the FITS headers, is the total integration
      time on the source without instrumental overheads such as time spent
      on the sky and observational inefficiencies caused by nod delays,
      chop-frame settling, and data-to-disk writes.  The data acquisition
      software for the LWS did not save the total time, including
      overheads, for one observation in the FITS headers.  Therefore,
      STOP_TIME is not provided.
 
 
    Processing
    ==========
      The LWS was operated in the chop-nod image mode, with nod throws of
      10 arcseconds North and East to acquire high and low airmass, blank
      sky frames along with comet frames for each observation.  Thus, each
      raw, six-dimensional FITS file produced by the LWS contains multiple
      of comet and blank sky frames.
 
      A two-dimensional FITS image was produced from each raw, six-
      dimensional FITS file by combining the frames in each chop-nod cycle
      into one, then stacking the chop-nod cycles.  For more details about
      the layout of the six-dimensional FITS files, refer to the instrument
      catalog file, CATALOG/LWSINST.CAT.  For more details about how the
      observers combined the frames within a six-dimensional FITS file,
      refer to the document file, LWS_CONVERT_FITS.TXT.
 
      The detector was flattened by making a median, low-airmass blank sky
      frame and a median, high-airmass blank sky frame, then subtracting
      the two sky frames.  For more details about this process, refer to
      the the document file, LWS_MAKE_FLAT.TXT.
 
      All observations were made using filters centered at 4.8 (M), 8.0,
      8.9, 10.7, 11.7, 12.5, 17.9 and 20.0 microns. Images of two bright-
      infrared standard stars, phi 1 Ceti and beta Andromedae, were used to
      calibrate the raw images of the comet.  Images of phi 1 Ceti were
      used for atmospheric extinction corrections at 10.7 microns.  Images
      of beta Andromedae were used for absolute flux calibrations and for
      atmospheric extinction corrections at the other wavelengths.  Details
      of the calibration steps are discussed in Fernandez et al. 2003
      [FERNANDEZETAL2003].
 
 
    Data
    ====
      This data set consists of 49 raw and reduced images, of which 14 are
      comet frames and 35 are standard star frames. Raw images are supplied
      as six-dimensional FITS image files with headers produced by the LWS
      data acquisition software.  Flattened, reduced images are supplied as
      two-dimensional, FITS image files. PDS labels for the raw and reduced
      data were generated by the Applied Coherent Technology Corporation
      and the Small Bodies Node. The tranmission profiles for the eight
      filters used for the observations are provided in this data set as
      ASCII tables.
 
      This data set also includes an ASCII table of the mid-IR fluxes of
      9P/Tempel 1 as measured by Fernandez et al. 2003 [FERNANDEZETAL2003].
      The authors attempted to calculate the albedo of the nucleus but
      noted it was difficult to measure because the coma was extensive in
      the simultaneous optical observations.
 
      The geometric circumstances of the comet and sky conditions from
      Fernandez et al. 2003 [FERNANDEZETAL2003] are reproduced here.
      Additional observing conditions, such as the mid-IR (MIR) seeing, are
      provided in Fernandez et al. 2003 [FERNANDEZETAL2003].
 
                                   20 Aug 2000
                                 ----------------------------------------
         Heliocentric distance   2.547 AU
         Geocentric distance     1.667 AU
         Phase angle             13.93 degrees
         MIR wavelengths         8.9, 10.7, 11.7, 12.5, 17.9, 20.0 micron
         Sky condition           Cirrus
 
      When displaying a FITS image from this data set using the directions
      provided by the LINE_DISPLAY_DIRECTION and SAMPLE_DISPLAY_DIRECTION
      keywords in the PDS labels, North is approximately down and
      East is to the right.
 
 
    Media/Format
    ============
      Data are supplied as electronic files in a PDS standard volume
      structure.  Filenames follow the ISO 9660 level 2 Interchange
      Standard so that a variety of computer systems can access the data.

Confidence Level Overview
    =========================
      Standard techniques were used for the reduction of the data and
      are documented in Fernandez et al. 2003 [FERNANDEZETAL2003].
 
      In the data labels, START_TIME + EXPOSURE_TIME/2 is not the
      mid-time of an observation.  This information is not availalbe
      and not readily calculable.  See the Parameters section of this
      file for more detail.
 
      The raw and reduced FITS filename have a prefix of 'FOCUS'.
      These are the original names provided by the observers.  None of
      the raw or reduced images in this data set are focus frames.
 
    Review
    ======
      This data set was reviewed in May 2004 and was approved for ingestion
      into the PDS Data Archive, pending the resolution of liens. Liens
      were resolved in December 2004.