Remko Scharroo (EUMETSAT, Germany); Cristina Martin-Puig (EUMETSAT, Germany); Bruno Lucas (HE SPACE, Germany); Carolina Loddo (EUMETSAT, Germany)

The Sentinel-3A SRAL Point Target Response (PTR) Half-Power Width is drifting over the time. This drift has been estimated to be around -0.5 mm per year and is significant, being five times the PTR width drift as measured for Envisat Altimeter and CryoSat-2 Altimeter.
In this work, we analyse the impact of this Sentinel-3A SRAL PTR width drift on the stability of the L2 marine geophysical measurement in both SAR and PLRM mode over the two years of the mission.
We will show how the PTR Width drift of -0.5 mm/year can give rise to a SWH (significant wave height) drift of around +1 cm per year in SAR mode which translates in a drift of SAR SSB (sea state bias) of about -0.3 mm per year.
If this SAR SSB drift is not compensated for, it will lead to an over-estimation of the SAR global sea level rise by the same amount.
The SAR SWH drift of around +1 cm per year is consistent with the current observations with respect to the ECMWF model and Jason-3 altimeter.
Finally, an algorithm to compensate for the SAR SWH drift (and hence SAR SSB drift) during the retracking time is proposed and hence validated with numerical simulations.