Some aspects of spatial aliasing in satellite altimetry
A detailed analysis on the effect of spatial aliasing associated with Topex/Poseidon-Jason, Geosat-GFO (Geosat Follow-On) and European Remote Sensing (ERS)-Envisat altimeters has been carried out. In the space domain, aliasing is characterized by a significant along-track (near meridional) and cross-track (near zonal) anisotropy in terms of alias wavelength, a. The former is practically limited by instrument noise at about 50 km, while the latter, ranging from 0 to ∞, is determined by the signal period, To. A striking feature of zonal alias wavelength is its step-like function with respect to signal period, which leads to a discrete distribution of the histogram of a versus To. This explains the coincidence that the S2 tide is always aliased at a wavelength of about 180° of longitude, and K1 and P1 at about 360° of longitude for all three groups of altimeters concerned. Potential consequences of spatial aliasing in satellite altimetry are also discussed. It is speculated that the intrinsic asymmetry in zonal and meridional aliasing may introduce artificial anisotropy in altimeter-derived geophysical parameters. Furthermore, it is shown that the consequences of spatial aliasing can be modified by other physical or oceanic processes such as the Doppler effect.