Data Set Overview
    =================
    Topographic spherical harmonic coefficients are derived from gridded 
    altimetry products via a numerical transform. The data are in the form 
    of tables with a detached label. The Reduced Data Record Software 
    Interface Specification describes the values input to the harmonic 
    transform.

    The discrete-Fourier-transformed topography coefficients H_j(m) at
    latitude index, times the associated Legendre polynomial P_lm, times a
    weight proportional to the area associated with a given latitude interval,
    are summed over all latitudes to yield the complex coefficient
    (C_lm,S_lm). The weights are normalized so that a coefficient of unit
    magnitude represents a harmonic whose squared amplitude integrated with
    respect to area over a unit sphere is 4 pi.

Overview
    ========
    Data are edited and selected before averaging so as to maintain
    good quality. Where necessary, crossover analysis is done prior to
    averaging so as to minimize discrepancies between individual tracks.

    Data Coverage and Quality
    =========================
    Each nominal monthly orbit provides roughly two tracks per degree of
    longitude at the equator. After each month's data are accumulated,
    crossover adjustments are made to minimize the difference in elevation
    between closely registered tracks and to remove along- and across-track
    orbital errors. The resulting dataset provides better geodetic control
    than that from individual tracks. The first release (March 15, 2010)
    does not incorporate these adjustments, and relies on preliminary
    trajectory solutions. Re-release with better precision and increased
    density will occur periodically.

    The current release does not include a gravity potential model.

    Limitations
    ===========
    Density of observations increases linearly with time. Higher-resolution
    SHADR products will be provided when data density provides coverage in a
    majority of pixels of each data product.