Andrey Kurekin (Plymouth Marine Laboratory, UK)

Retracking' is conventionally performed on a single waveform at a time, and the shape parameters from multiple along-track estimates then consolidated into lower frequency (typically 1 Hz) observations. From physical considerations one would expect the true shape parameters to be slowly-varying within the 1-second interval, but this is not normally taken into consideration. In this work, sponsored by ESA's Sea Level CCI programme, we evaluate an approach that analyses 21 or more waveforms at once, modelling the gradual changes in the shape parameters. Such an approach would have been impractical a decade ago, because of the greater number of unknowns to be determined, but modern processors with advanced techniques for locating a minimum in multi-dimensional space make this approach feasible.
Having shown that the technique works well for the open ocean, where (in the absence of rain cells or surface slicks) ocean waveforms change gradually, we are now testing it in the coastal zone, where sheltering by headlands and shoaling bathymetry may make both wind and wave conditions vary appreciably. We specifically explore Envisat passes that run close to well-maintained tide gauges. The ones selected cover a range of conditions from the relatively enclosed Irish Sea to La Coruna and Brest which are exposed to North Atlantic swell.