Data Set Overview
    =================
      The NEAR Laser Rangefinder (NLR) Level 3 Data Products includes
      spherical harmonic shape and gravity models, and gridded maps
      or images of those models.
 
    Parameters
    ==========
      Spherical harmonic models are tables of coefficients GM, Cmn,
      and Smn. ASCII data type (SHA) formats are defined. Each file
      contains 2 tables: a header table containing general
      parameters for the model (gravitational constant, its
      uncertainty, degree and order of the field, normalization
      state, reference longitude, and reference latitude) and a
      coefficients table (degree m, order n, coefficients Cmn and
      Smn, and their uncertainties).
 
      Gridded Digital Map files are image representations
      of shape and other parameters. Gravity and topographic values
      may be displayed using this data type.  Data are formatted
      as PDS image objects.
 
    Processing
    ==========
      The Level 2 NLR profiles in the 200 by 200 km orbital phases and
      lower are the source of the NLR shape models. Where two ground
      tracks intersect, the residual is calculated by linear
      interpolation between adjacent shots. The crossover residuals are
      used as a measure of data quality and can be used to remove
      systematic errors in spacecraft ephemeris and pointing. Crossover
      corrections are implemented in two stages via the software described
      in [NEUMANNETAL2001], as modified for NLR. The first stage adjusts
      for long-wavelength errors due to mis-modeled ephemeris and pointing,
      at a period of four cycles per asteroid revolution.
      The second stage adjusts higher-frequency errors at a period of ~5
      minutes, primarily due to residual pointing mismodeling. Adjustments
      are iterated until the crossover residual root-mean-square error is
      less than 10 m.
 
      The adjusted profiles are merged by binning observations within a
      given grid cell, uniformly spaced in longitude and latitude. The
      median value and the number of observations in each bin comprise the
      gridded data product.
 
      The gravity field coefficients were obtained by solving systems
      of equations with thousands of unknowns.  Radio tracking data
      in long arcs delimited by propulsive maneuvers, occultations,
      etc. were used in solutions that were obtained iteratively
      and by least squares.
 
    Data
    ====
      Data are stored on CD-WO volumes. A CD volume was created
      for delivery of data to PDS.
 
      ASCII spherical harmonic models are stored in the /LEVEL3/SHA
      directory with file names of the form NLRknnnv.SHA, where nnn
      is a 3-character modifier specified by the data producer, v is a
      version identifier, and k is replaced by G for gravity field or
      T for topography/shape field, and SHA denotes that this is an ASCII
      file of spherical harmonic coefficients.
 
      Gridded map products are stored in the /LEVEL3/IMG directory.
      Each image is a binary array of 16-bit integers with one image line
      per file record. The image file name is in the form NLRnnnvk.IMG,
      where nnn is the bin size, v is a version identifier, and k is
      replaced by C for counts or R for radius, and IMG denotes that
      this is a PDS image object. For example, a one-eighth degree
      resolution topography image would be named NLR125vR.IMG. Its format
      would be described by a detached PDS label in the file NLR125vR.LBL.
 
      An ASCII tabular file containing global shape data of Eros,
      including the latitude and longitude of the NLR laser bounce
      point, the radius, and the number of observations (counts) can be
      found in the /LEVEL3/ASCII directory.
 
    Ancillary Data
    ==============
      None.
 
    Coordinate System
    =================
      NLR data files use an EROS centered body-fixed coordinate
      system with positive east longitude. The transformation from
      inertial (J2000) coordinates to body-fixed is represented by the
      project-supplied SPICE format attitude and orientation files used
      to generate level 2 data products.
 
    Software
    ========
      None.
 
    Media/Format
    ============
      The archival data set was written on CD-WO by the NEAR/NLR
      Project.  The CD-WO volumes conform to ISO 9660 Level 2
      standards.

Overview
    ========
      Data in this archive have been reduced as part of mission data
      analysis activities of the NEAR/NLR Science Team.
 
    Review
    ======
      This archival data set was reviewed by the NEAR/NLR Science
      Team prior to final submission to the Planetary Data
      System (PDS).
 
      Prior to creation of the final version of the archival data
      set, key elements of the archive were distributed for
      preliminary review.  These included electronic versions of
      example PDS labels, example data files, CATALOG files, and other
      relevant documentation.  These materials were distributed to
      PDS personnel, the experiment investigator, and others, as
      appropriate.
 
    Data Coverage and Quality
    =========================
      These volumes contain gravity and shape models and gridded maps
      generated from NEAR data collected through February 2001.
      The NEAR data included tracking results from the EROS Orbit
      Phase.
 
      GTM0180A.SHA contains the coefficients for a 180x180
      degree and order shape model produced at Goddard Space Flight
      Center. A full error analysis is included.
      Internal consistency, as measured by crossover point misfit,
      is generally better than 10 m.
 
      NLRG016A.SHA is a spherical harmonic gravity field model
      complete to degree and order 16.
 
      NLR125AR.IMG is a gridded shape map of Eros at a
      resolution of 0.125 by 0.125 degrees, based on altimetry data
      acquired by the NLR instrument. The data include edited NLR
      observations from 200-km orbits and lower, using the NLR393
      orbit solutions produced at NASA-GSFC.
 
      NLR125AC.IMG is a data file that accompanies the shape
      map of Eros NLR125AR.IMG at a resolution of
      0.125 by 0.125 degrees. It contains the number of observations
      per pixel that have been used to produce the NLR shape data
      product. The data include edited NLR observations from 200-km
      orbits and lower.
 
      NLR100.TAB is a 1 degree resolution tabular data file that
      contains global shape data of Eros, including the latitude and
      longitude of the NLR laser bounce point, the radius, and the
      number of observations (counts).
 
    Limitations
    ===========
      There is NO gravity covariance matrix on these volumes.
      This product is useful in understanding the errors in the gravity
      solution. The gravity field covariance represents the complete
      error description for the gravity field solution, including the
      coefficient variances (sigmas^2), and the correlations between
      all the coefficients.
      This product was not available at the time this archive was
      completed. The file and documentation will be available at a
      later date on the World Wide Web/Internet at the following URL:
           http://pds-geophys.wustl.edu/pds/near_nlr.