This data set description was provided by Stephanie McLaughlin and
  Dennis Wellnitz (University of Maryland), who participated in
  the ground calibration tests of the Deep Impact instruments.
 
 
Data Set Overview
=================
 
  This data set contains raw images acquired by the Imaging Targeting
  Sensor's Visible CCD (ITS) during the third preflight thermal-vacuum
  test (TV3) for Deep Impact.  The experiments performed during TV3
  were designed by the Ball Aerospace team with input from the science
  team.  TV3 was conducted by Don Hampton of Ball Aerospace.  Several
  science team members were present at all times to assist with the
  experiments and perform real-time analysis of the data.
 
  The main objective of the TV3 was to test and obtain calibration data
  of the ITS at or below the expected operating temperature, 243K,
  during the encounter with comet Tempel 1.  Tested calibrations were
  designed to:
 
    - Determine best focus
    - Test the photo-response of the CCD by using several calibrated
      blackbody sources and obtain flats
    - Measure linearity of the CCD
    - Measure dark current as the CCD cooled
    - Measure bias
 
  To meet these objectives, the ITS was tested in the Ball 8
  thermal-vacuum chamber; its shroud was cooled with liquid nitrogen.
  An optical test bench was setup outside the chamber and oriented
  such that light produced by a source would enter the chamber's window
  and into the ITS telescope.  Various types of visible-wavelength
  sources were used to test the ITS.
 
  TV3 activities are summarized in the following chart.
 
    Date Range/(DOY)           Tests
    -------------------------  ----------------------------------------
    2003-01-16 to 2003-01-23   Warm tests of the ITS in a clean
    (016-023)                  room including horizontal focus,
                               astigmatism, geometric distortions,
                               illumination by a blackbody
 
    2003-01-24                 ITS instrument package installed
    (024)                      in the Ball 8 thermal-vacuum chamber
 
    2003-01-25 to 2003-01-26   Instrument bakeout
    (025-026)
 
    2003-01-27 to 2003-01-29   Instrument cooldown; Dark current;
    (027-029)                  Images of the interior of the TV
                               chamber, a uniform source
 
    2003-01-30                 Instrument is cold (226-233K);
    (030)                      Flats using various blackbody sources;
                               Bias; Linearity; Latency; Dark current
 
  For more information about the mission, the ITS instrument, the
  anticipated flight data, and the cratering experiment, see
  A'Hearn, et al. (2005) [AHEARNETAL2005], Hampton, et al. (2005)
  [HAMPTONETAL2005], Klaasen, et al. (2005) [KLAASENETAL2005],
  Richardson, et al. (2005) [RICHARDSONETAL2005], and
  Schultz and Ernst (2005) [SCHULTZ&ERNST2005].
 
 
Parameters
==========
 
  The image data are in units of raw data numbers.  For TV3, all
  nine of the image modes, also known as instrument modes, for the
  ITS were tested:
 
    Image  MinExp  X-Size  Y-Size
    Mode#   (ms)   (pix)   (pix)   Binning  Comments
    -----  ------  ------  ------  -------  -------------------------
      1      3.5    1024    1024     1x1    Shuttered
      2      3.5     512     512     1x1    Shuttered
      3      3.5     256     256     1x1    Shuttered
      4    217.8     256     256     1x1    Not shuttered
      5      3.5     128     128     1x1    Shuttered
      6     98.4     128     128     1x1    Not shuttered
      7     47.4      64      64     1x1    Not shuttered
      8     47.4      64      64     1x1    Not shuttered,no overscan
      9      3.5    1024    1024     1x1    Shuttered; diagnostic
 
  In this table, MinExp is the minimum exposure time and the term
  shuttered means the light blocker in the ITS instrument is
  always used (opened and closed). For all modes, additional exposure
  time can be commanded.  For unshuttered modes, a delay time (duration
  to wait before the start of the CCD readout) can also be commanded.
  For more information about the image modes, see Hampton, et al. (2005)
  [HAMPTONETAL2005].
 
 
Data
====
 
  Images
  ------
 
    The data are in the form of FITS files with attached FITS headers
    and detached PDS labels. One data files contains one ITS image.
    The fastest-varying axis is considered the X axis and the
    slowest-varying, the Y axis.  TV3 data filenames have this format:
    Iyymmdd_hhmmss_sss_x.FIT where the 'yymmdd_hhmmss_sss' string the date,
    time and subseconds stamp provided by the ground-support computer
    when it stored the original data file.  The clock on the ground-support
    computer was set to local Mountain time.  The 'x' string is valued with
    'A' for CCD data.
 
    For TV3, the ground-support computer stored data files in a native
    image format, called 'IMG'.  The raw data numbers were 14-bit and
    and left justified.  A 100-byte image header was pre-pended to each
    data array.  The 'IMG' data were converted to FITS at the Deep Impact
    Science Data Center (SDC) at Cornell University, using algorithms
    developed by Ball Aerospace for testing of the instruments and to
    allow real-time analysis of data during thermal-vacuum tests.
    During the conversion, raw data numbers were right justified to
    give the actual, true data numbers.  Data in the 100-byte image
    header are captured in the FITS header.
 
    All images ITS image modes except 8 and 9 have overclock data
    in the outermost rows and columns of the image array.
 
  Instrument Temperatures
  -----------------------
 
    Temperatures at various locations on the ITS were automatically
    recorded about every 5 minutes by a thermister monitor, a computer.
    Temperature data, in fixed-width ASCII table format, is available
    in the DATA/TEMP_LOG.  Time stamps in the temperature file are
    within several minutes of the time stamps in the FITS filenames.
 
         .
Ancillary Data
==============
 
  The DOCUMENT directory provides an image log recorded during TV3.
  The log contains an entry for each image acquired during TV3 and
  includes image parameters such as mode and experiment type.  The
  log includes a brief description of each type of experiment performed
  during TV3 and a summary of experiments performed on each test date.
 
  The DOCUMENT directory also provides daily reports written by the
  test leaders and distributed to the test team and the science
  team.  The reports describe in detail the test activities as well
  problems and successes encountered during TV3.
 
  The DOCUMENT directory includes the local PDS data dictionary used
  to produce the labels.
 
 
Media/Format
============
 
  This data set is released as a logical data volume.

1) The time stamp in the FITS filename can vary by several
       tens of seconds of the actual time the image was acquired.
 
    2) Instrument temperatures should be extracted from the temperature
       table provided in this archive.  While some temperatures appear
       in the PDS labels, these values were extracted from the FITS
       headers and are not reliable because of uncertainties about
       how the measurements were being recorded by the ground-support
       equipment used during TV3.  However, temperatures recorded by
       the thermister monitor and provided in the temperature table
       are reliable according to Ball Areospace engineers and science
       team members who have used these data.
 
    3) The project elected store and archive ITS FITS images from
       flight with the sky orientation during the approach to Tempel 1:
       East is to the left and North is up.  However, ITS FITS images
       from TV3 were stored in the engineering orientation with
       East to the right and North up.  When comparing ITS FITS images
       from TV3 to those acquired during flight, a left-to-right flip
       about the y axis is required for the TV3 data.
 
    4) The images in this archive were used extensively by the science
       team and Ball Aerospace engineers to verify the instruments were
       operating within requirements and to calibrate the instruments.
       These data were reviewed internally by the Deep Impact project
       before release to the planetary community.