Aliasing of high-frequency variability by altimetry: Evaluation from bottom pressure recorders

In spectra computed from bottom pressure records, 18% to 63% of non-tidal energy is associated with frequencies greater than 1 cycle per 20 days, the approximate Nyquist frequency for the TOPEX/Poseidon (T/P) satellite. Since bottom pressure measurements are correlated with coincident sea surface height measurements from the T/P satellite, hourly bottom pressure data are used here to characterize the aliasing expected from T/P. As numerical modeling studies have also demonstrated, spectra computed from data sampled at 10-day intervals are likely to alias substantial amounts of unresolved high-frequency variability, particularly at frequencies greater than 0.2 times the Nyquist frequency.