A Detailed View of the South-Pacific Geoid from Satellite Altimetry

Sandwell, DT.  1984.  A Detailed View of the South-Pacific Geoid from Satellite Altimetry. Journal of Geophysical Research. 89:1089-1104.


Images of sea surface undulations in the South Pacific have been constructed from GEOS 3 and SEASAT altimeter data. Height discrepancies at crossover points, associated with long-wavelength radial orbit error, were suppressed by taking along-track derivatives of the ascending and descending profiles. These geoid slopes were then rotated and scaled to produce the north and east components of the deflection of the vertical. Finally, the results are displayed by using the hill shading technique, where gray-tone images represent the innner product of the deflection vector with an assigned sun vector. Less apparent sea surface undulations can be enhanced by varying the sun's zenith and azimuth. Shorterwavelength sea surface undulations reflect seafloor topography. For instance, fracture zones (FZ's) appear as elongated sharp steps in the sea surface, while seamounts produce circular bumps. Since large areas of the South Pacific are unsurveyed, many previously undetected features appear on the images. Comparisons with bathymetric charts reveal 72 uncharted seamounts having geoid expressions greater than or equal to Easter Island's expression. The dominant features in the images, however, are the large age-offset FZ's such as the Eltanin and Udintsev FZ's. The images reveal that the Eltanin FZ is connected to the Louisville Ridge; combined they produce a continuous geoid signature across most of the South Pacific. This supports the hypothesis of Hayes and Ewing (1968) that the Louisville Ridge is the northwest extension of the Eltanin FZ.