Seasat altimetry and the South Atlantic geoid: 1, Spectral analysis, d

This paper presents a discussion of the spectral characteristics of geoid profiles derived from Seasat alitmetry in the South Atlantic. Individual profile spectra are computed and averaged in seven separate geodynamic provinces (Mid-Atlantic Ridge, flanks, Walvis and Rio Grande aseismic ridges, and Argen-tine and Cape basins). Three distinct wavebands can be identified in most spectra. For wavelengths shorter than 35 km the spectra are typical of white noise with a 7-cm rms amplitude typical of Seasat altimeter measurement noise. For wavelengths between 300 and 800 km (our uppermost limit, since original profiles are 1700 km long) the spectra are in reasonable agreement with Kaula's empirical rule and are compatible with a Pratt (thermal boundary layer) compensation mechanism, with an ill-defined compensation depth of 30-60 km. The paper centers on the description of the 35-300 km part of the spectra. Computation of an impedance for each province requires good knowledge of its bathymetry, which is far from satisfactory as yet in the South Atlantic. We show that for wavelengths longer than 80 km the squared amplitude spectrum of bathymetry varies as the inverse of wave number. We propose that this relationship might also hold at shorter wavelengths, although it is not observed due to presently insufficient data. Using these spectral estimates, and correcting for the mean depth of the topography, we derive impedance (actually response function) estimates eparately for each province. The data are wel