Data Set Overview
  =================
    This CD contains portions of the Clementine HiRes Lunar Mosaic, a
    geometrically controlled, calibrated mosaic compiled from
    non-uniformity corrected, 750 nanometer ('D') filter high
    resolution observations from the HiRes imaging system onboard the
    Clementine Spacecraft.  These mosaics cover sub-polar regions
    between 80 deg S and 80 deg N with the sinusoidal equal area
    mapping at 20 m/pixel, and the polar regions above 80 deg with a
    stereographic mapping at 30 m/pixel resolution at the poles.  The
    geometric control is provided by the 100 m/pixel USGS Clementine
    Basemap Mosaic (PDS CD-ROM Volumes CL_3001-3015) compiled from
    the 750 nm Ultraviolet/Visible Clementine imaging system and, for
    the polar mosaics, from the 150 m/pixel polar basemap mosaic.
    Calibration was achieved by removing image nonuniformity largely
    due to the HiRes system's light intensifier.  Also provided are
    offset and scale factors which transform the 8-bit HiRes data to
    approximate photometric units, achieved by a fit of the HiRes
    data to the corresponding UV/Vis basemap, which is
    photometrically calibrated.
 
    The mosaic on this CD covers polar regions above 80 degrees.  The
    mosaics are divided into square tiles 2250 pixels on a side,
    which spans approximately 2.2 degrees.
 
    This CD also contains ancillary data files that support the HiRes
    Mosaic.  These files include browse images with UV/Vis context
    stored in a JPEG format, HTML documents that support a web
    browser interface to the CDs, index files ('imgindx.tab' and
    'srcindx.tab') that tabulate the contents of the CD, and
    documentation files.  For more information on the contents and
    organization of the CD volume set refer to the 'FILES,
    DIRECTORIES AND DISK CONTENTS' section of this document.
 
    Using a web browser open the 'index.htm' file located in the
    'root' directory of the CD.  The html document will direct you to
    other informational documents and the image browser for rapidly
    viewing the image collection.
 
 
  Parameters
  ==========
    N/A
 
 
  Processing
  ==========
    Processing proceeded an orbital and latitude 'bin' basis,
    reflecting the organization of the Clementine EDR CDs.  A
    latitude bin comprises all images of a given orbit deemed to fall
    within a 10 degree latitude range based on SPICE information.
    The latitude ranges are defined to fall on on 10-degree
    boundaries from -90 to +90.  For the sub-polar mosaics, map
    projection of images from a given orbit used the same central
    longitude, taken to be the orbit's longitude at the lunar
    equator.  Images used in the polar mosaics were warped to a
    common stereographic projection relative to the pertinent pole.
 
    The HiRes Mosaic processing comprised 5 steps: (1) Image
    calibration, map project and basemap generation; (2) Low
    resolution registration against the UV/Vis basemap; (3) High
    resolution registration against overlapping images; (4)
    Constrained placement combining high- and low-resolution
    registrations; and (5) HiRes mosaic and photometric calibration
    estimation.
 
    Placement and calibration for the polar mosaics differed in some
    regards from those of the sub-polar mosaics.  Due to illumination
    paucity, various polar locales lacked useful geometric and
    photometric control.  In these regions, registration between
    individual HiRes frames, both with and among orbits, was the
    primary placement guide.  Such placement was anchored to images
    which did have reliable registration against the UV/Vis basemap.
    For convenience, rectangular zones centered on the poles were
    defined within which placement proceeded in this manner.
 
    Similarly, the basemap photometric calibration was considered
    unreliable at the highest latitudes, and so for a given HiRes
    polar mosaic, a single calibration (based on well-illuminated
    tiles and basemap portions) was adopted for the entire mosaic,
    rather than defining one for each individual tile.
 
 
  Media/Format
  ============
    The Clementine basemap is delivered to the Planetary Data System
    using CD media.  Formats are based on standards for such products
    established by the Planetary Data System (PDS) [PDSSR1992].

Confidence Level Overview
  =========================
 
    Geometric Accuracy
    ------------------
      The geometric placement of the HiRes Mosaics is based primarily
      on registration with the Clementine Basemap Mosaic, which has
      accuracies approaching the UV/Vis scale.  The UV/Vis accuracy
      is discussed below, drawing extensively from the UV/Vis Basemap
      Mosaic documents.
 
      The goal of the UV/Vis basemap was for 95% of the Moon
      (excluding the oblique observation gap fills) to have better
      than 0.5 km/pixel absolute positional accuracy and to adjust
      the camera angles so that all frames match neighboring frames
      to within an accuracy of 2 pixels.
 
      Approximately 265,000 match points were collected at the USGS
      from ~43,000 UV/Vis images, providing global coverage.  About
      80% of these points were collected via autonomous procedures,
      whereas the 20% required the more time consuming but highly
      accurate manual pattern-recognition.  The oblique gap-fill
      images were the most difficult to match, and required
      substantial human intervention.  Matching the polar regions was
      time-consuming because each frame overlaps many other frames.
      Most match points were found to a precision of 0.2 pixels.
 
      The USGS match points were sent to RAND corporation for
      analytical triangulations.  Using these match points, control
      points from the Apollo region, and the latest NAIF/SPICE
      information, RAND determined improved camera orientation angles
      for the global set of UV/Vis images.  A spherical Moon of
      constant radius (1737.4 kilometers) was assumed, which was a
      significant source of error near the oblique gap fills.  The
      analytical triangulation is a least-squares formulation
      designed to adjust the latitude and longitude of the control
      points and the camera orientation angles to best fit the match
      points.  The final (global) analytical triangulation required
      solving ~660,000 normal equations.  The mean error is less than
      1 pixel.  This is by far the largest analytical triangulation
      ever applied to a planetary body other than Earth.  The results
      fully define the planimetric geometry of the basemap, to which
      future systematic products, such as the present HiRes Mosaic,
      should be tied.
 
      Accurate placement of the map-projected HiRes images was
      accomplished by combining registration to the UV/Vis basemap at
      the basemap's resolution (100 m/pixel and 150 m/pixel) with
      registration of overlapping HiRes pairs at five times this
      resolution (20 m/pixel and 30 m/pixel).  The registrations were
      facilitated with automated image correlation.  These
      registrations were combined in a Least Absolute Deviation fit
      [BARRODALE1980] constrained to stray no further than some small
      amount from the basemap-scale registration.  Use of the least
      absolute deviation gives outliers less importance than does a
      least squares fit.  Further manual placement of 1-5 percent of
      the image was required; these were due either to poor initial
      placement, particularly when the scene was featureless and
      provided few or no overlapping features with the UV/Vis
      basemap, or to mismatches of scene, resolution or illumination
      across seams in the UV/Vis mosaic.  Some misregistration of
      adjacent HiRes images remains in the final mosaic because the
      paramount goal was registration with the underlying UV/Vis
      Basemap Mosaic.
 
      As described above, the HiRes polar mosaics lacked Uv/Vis
      basemap registration in shadowed regions, most notably at and
      immediately adjacent to the poles.  In such locales, the
      placment of HiRes images was guided primarily by registration
      of individual HiRes frames within and among orbits.  Such
      placement was applied within approximately 2 degrees of the
      poles.
 
  Radiometric Units
  =================
    To date, absolute photometric calibration of the HiRes image data
    remains elusive.  This seems particularly problematic for the
    bulk of HiRes images, which were noisy due to the low gain
    setting intended to extend the lifetime of the imaging system.
    For these reasons, a piece-wise intensity matching of the HiRes
    Mosaics to the UV/Vis Basemap Mosaic was adopted as an
    approximate radiometric calibration.  The further decision was
    made to use 750 nm ('D') filter HiRes images in order to best
    match the UV/Vis Basemap Mosaic, which dominantly comprises 750
    nm ('B') filter images.  A more detailed description of the
    UV/Vis basemap photometric calibration may be found on the UV/Vis
    basemap volumes CL_30XX.
 
    Whereas sub-polar HiRes tiles were individually calibrated
    against the underlying UV/Vis basemap, each of the four HiRes
    polar mosaics have a single calibration for all tiles.  This is
    due to the difficulties associated with calibrating regions
    perennially in shadow, which renders some portions of the
    underlying polar basemap calibration unreliable.  To mitigate
    this problem, a well-illuminated tile and basemap portion near 85
    deg latitude from each mosaic was adopted as calibration
    references.
 
    This calibration is embodied by the header values of the OFFSET
    and SCALING_FACTOR entries, which defines HiRes fractional
    reflectances:
 
    OFFSET
 
    where: DN = 8-bit pixel value of HiRes mosaic image array.
                SCALING_FACTOR units are fractional reflectance per DN
                OFFSET units are fractional reflectance
 
    The calibration in every case included correction for the
    non-uniformity of the raw HiRes images due to the light
    intensifier.