Analyzing altimeter artifacts: statistical properties of ocean waveforms

In this paper waveforms, that is, returns from the ocean surface, from a number of spaceborne radar altimeter instruments [European Remote-sensing Satellites (ERS-1 and -2), TOPEX, and Poseidon] are examined. This is the first paper to analyze waveform data from a number of altimeters in a consistent manner. Mean shapes and various statistical properties (bin-to-bin correlations, number of independent samples) were determined and the authors comment on their anomalies. The analyses were performed for data over the deep ocean, as that is the best understood surface. However, the determined functional characteristics of the individual altimeters are applicable to their operation over all surfaces. The implications of the existence of these anomalies for the retrieval of geophysical parameters from radar altimeter data are discussed. It is argued that the need for physically based theories, in order to understand radar altimeter returns from the ocean (or indeed any other) surface, implies a need for the engineering and software design of the instrument to be such as to avoid spurious anomalies in the waveforms.