Effects of unresolved high frequency signals in altimeter records inferred from tide gauge data

Author: Rui M. Ponte and F. Lyard
Date: 
April 1, 2002
Type: 
Journal Article
Venue: 
Journal of Atmospheric and Oceanic Technology
Citation: 

Ponte, R.M., and F. Lyard, 2002. Effects of unresolved high frequency signals in altimeter records inferred from tide gauge data, Journal of Atmospheric and Oceanic Technology, 19, 534-539.

Rapid sea level signals are poorly resolved, or "aliased," by the TOPEX/Poseidon altimeter, due to its ∼10-day repeat cycle (Nyquist period TN∼ 20 days). To assess the potential for temporal aliasing in the altimeter data, the authors analyze hourly sea level records from a set of 110 island and coastal tide gauges. Time series are detided to focus on nontidal effects. Large variance is found at periods <TN (more than 50% of the total variance at high latitudes), with important contributions from the shortest periods (<2 days). The inverted barometer correction reduces high-frequency variance at mid- and high latitudes but not at low latitudes. As inferred from the tide gauge analysis, in the worst-case scenario (one data point per altimeter repeat cycle), the ratio of aliased to measured variance can range from ∼0.1 at the annual period to ∼0.8 near TN. Moderate data averaging (three points per altimeter repeat cycle, given a ∼3.3-day near-repeat orbit) can substantially reduce the aliasing, however. The impact of aliasing is, in general, worse for coastal than for island stations.