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 i