A comparison is made between GEOS-3 and SEASAT altimeter data with regard to noise power spectral density (PSD), derived geoid PSD, and short wavelength resolution. At wavelengths greater than 450 km the noise PSDs for GEOS-3 and SEASAT are essentially the same and are attributed to mesoscale oceanographic effects. At shorter wavelengths the noise spectra diverge because of the higher GEOS-3 instrument noise. The average along-track geoid PSDS are nearly identical between wavelengths of 4500 and 72 km. The spectral coherence between repeat tracks shows that the short wavelength resolution of SEASAT data is ≈32 km, and for GEOS-3 it is ≈60 km.