Abstract
Abstract. It is becoming well known that aliasing associated with ocean tides could be a major source of systematic error in altimeter sea-level measurements, due to asynoptic sampling and imperfect tide modelling. However, it has been shown that signals of non-tidal origin may also contribute significantly to the observed aliasing. In this paper, numerical simulations are performed to demonstrate the full aliasing potential associated with altimeter observations of seasonal sea-level variability and annual Rossby waves. Our results indicate that ignorance of non-tidal aliasing may lead to the possibility of underestimating the total aliasing and misinterpreting or overlooking existing geophysical phenomena. Therefore, it is argued that an entire aliasing picture should be kept in mind when satellite altimeter data are analysed.
Highlights
The accuracy of altimetric sea-level measurements has been steadily improving towards a striking level of 1±2 cm during the past few years (Fu et al, 1994; Cheney et al, 1994; Stammer and Wunsch, 1994; Shum et al, 1995; Le Traon et al, 1995), thanks to the signi®cant advances in satellite technology, remotesensing instruments, as well as geophysical modelling and data processing
Alias problems in satellite altimetry are usually addressed in connection with ocean tides, which are most detectable due to their well-de®ned frequencies associated with high energies
The signals are known to have periods of less than 20 days and they are certainly not annual Rossby waves, the possibility of their Rossby-wave origin cannot be completely ruled out. It is worth mentioning the recent ®nding by Chelton and Schlax (1996) that the TOPEX/POSEIDON-observed propagation speeds of Rossby waves are systematically higher than those predicted from standard theory
Summary
The accuracy of altimetric sea-level measurements has been steadily improving towards a striking level of 1±2 cm during the past few years (Fu et al, 1994; Cheney et al, 1994; Stammer and Wunsch, 1994; Shum et al, 1995; Le Traon et al, 1995), thanks to the signi®cant advances in satellite technology, remotesensing instruments, as well as geophysical modelling and data processing. With considerable minimization of the uncertainties in orbit determination and environmental corrections, an intrinsic systematic source of error in altimeter measurements known as aliasing, resulting from asynoptic sampling, becomes an emerging challenge to many geophysical applications This can be seen from the fact that, in recent altimetric studies, aliasing is a frequently mentioned source of error Numerical experiments are designed under previously developed theory to simulate the overall aliasing involved in each case These two examples are selected because, on one hand, they are geophysically important and observationally favourable; and on the other, they are aliasing representative and cover all four dimensions of the problem.
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