Alejandro Egido (ESTEC/ESA, Netherlands); Doug Vandemark (University of New Hampshire, United States); Luciana Fenoglio (University of Bonn, Germany); Walter H.F. Smith (NOAA, United States); Eric Leuliette (NOAA, United States)

During more than a decade, synthetic aperture radar (SAR) altimetry continues to open more insights and possibilities about the sea state. During the commissioning of Sentinel-6MF, comparisons of SAR-processed high resolution (HR) and low resolution (LR) products showed that HR sea surface height (SSH) and significant wave height (SWH) estimates are significantly biased. The latter effect can be explained with vertical wave particle velocities causing an azimuth blurring effect leading to SWH biases (Buchhaupt et al. 2023). On the other hand, the SSH biases in HR point towards a dependency with respect to the wind speed projected towards the flight path of the satellite causing a scaling of the Doppler frequencies (Buchhaupt et al., submitted).

This study aims towards a more detailed investigation of surface velocity impacts on HR measurements. We will present an analysis of one year of processed Sentinel-6MF L1A data. The processing will be performed by our in-house experimental L1A data processor. We will discuss how different retrackers behave with respect to SSH and SWH biases in SAR mode and how to mitigate them in future evolutions of the S6 Payload Data Acquisition and Processing (PDAP).

The considered retrackers shall be:
1. SINCS STD: Numerical 3 parameter waveform retracker (wind-speed, SSH and SWH).
2. SINCS-OV ZSK: Numerical SAR stack retracker estimating wind-speed, SSH, SWH and the standard deviation of vertical velocities, sigmav.
3. SINCS-OV2 ZSK: As SINCS-OV ZSK, but with additional parameter describing the Doppler frequency scaling caused by mean line-of-sight surface velocities, ux.

The results will be validated with respect to LR and the ERA5 wave model.