The ALES+ SAR Service for Cryosat-2 and Sentinel-3 at ESA GPOD

Marcello Passaro (Deutsches Geodätisches Forschungsinstitut der Technischen Universität München (DGFI-TUM) , Arcisstraße 21, 80333 Munich, Germany, Germany)


Marco Restano (SERCO c/o ESA/ESRIN, Italy); Giovanni Sabatino (Progressive Systems/ESRIN, Frascati, Italy, Italy); Carla Orrú (Progressive Systems/ESRIN, Frascati, Italy, Italy); Jérôme Benveniste (ESA-ESRIN, Largo Galileo Galilei 1, 00044 Frascati, Italy, Italy)

Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)

Session: Outreach, Education and Altimetric Data Services

Presentation type: Type Forum only

Water level from sea ice-covered oceans is particularly challenging to retrieve with satellite radar altimeters due to the different shapes assumed by the returned signal compared with the standard open ocean waveforms. Valid measurements are scarce in large areas of the Arctic and Antarctic Oceans, because sea level can only be estimated in the openings in the sea ice (leads and polynyas). Similar signal-related problems affect also measurements in coastal and inland waters.

In Passaro et. al 2018. the ALES+ SAR retracking strategy, based on a sub-waveform retracker that is able to adapt the fitting of the signal depending on the sea state and on the slope of its trailing edge, was presented. The algorithm modifies the existing Adaptive Leading Edge Subwaveform retracker originally designed for coastal waters (Passaro et. al, 2014), and was applied to ENVISAT and ERS-2 missions.

In the frame of the current ESA Baltic+ SEAL project (, the ALES+ retracker has been further developed and extended to all the missions considered (ERS-2, ENVISAT, Jason-1/2/3, SARAL/AltiKa, Cryosat-2, Sentinel-3A/B).

In particular, ALES+ for LRM is based on the Brown-Hayne functional form that models the radar returns from the ocean to the satellite, whereas for SAR waveforms it adopts a simplified version of the Brown-Hayne functional form as an empirical retracker to track the leading edge of the waveform. This empirical application of the Brown-Hayne model implies that ALES+ cannot estimate a physical value of SWH and of
Marcello Passaro
Deutsches Geodätisches Forschungsinstitut der Technischen Universität München (DGFI-TUM) , Arcisstraße 21, 80333 Munich, Germany