ALES for AltiKa: application of a subwaveform retracker to high frequency sea level estimation

Marcello Passaro (NOC Southampton - ESA ESRIN, United Kingdom)


Graham Quartly (Plymouth Marine Laboratory, United Kingdom); Jérôme Benveniste (European Space Agency - ESRIN, Italy)

Event: 2014 SARAL/AltiKa workshop

Session: Oceanography

Presentation type: Type Poster

Conventional high-rate AltiKa waveforms are distributed at 40 Hz (~165m along-track resolution) by averaging sets of 96 individual echoes (IEs). The Adaptive Leading Edge Waveform Retracker (ALES), which has been successfully validated in conventional altimetry missions in open ocean and coastal areas, is now tuned to retrack AltiKa waveforms and tested against in-situ sea level estimations. ALES characteristic is the capability to select a subwaveform that contains the leading edge and as many gates as needed to maintain the accuracy of an open-ocean full waveform retracker, depending on an initial Significant Wave Height (SWH) estimate.

We speculate that ALES is particularly suitable to retrack AltiKa waveforms at an even higher frequency (>40 Hz), since averages of as few as 8 IEs already show a clearly distinguishable leading edge, while the high noise in the trailing edge does not influence the selected subwaveform, particularly at low SWH. Starting from individual echoes for selected AltiKa tracks, groups of 8 to 32 IEs are averaged and retracked. The accuracy of ALES estimates is evaluated considering the number of IEs averaged and the sea state.

With the aim to obtain a more precise sea level estimation, this study can pave the way for the use of a selective average to build a 40 Hz waveform particularly in coastal areas, where corrupted IEs that add significant noise to the averaged echo could be excluded.

Marcello Passaro
NOC Southampton - ESA ESRIN
United Kingdom