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The Sentinel-6 Michael Freilich (S6-MF) satellite was launched on 21st November 2020. Poseidon-4, the main payload onboard S6-MF, is the first synthetic aperture radar (SAR) altimeter operating in an interleaved open burst mode. In this study, the sea surface height (<i>SSH</i>), significant wave height (<i>SWH</i>) and wind speed observations from the Poseidon-4 Level 2 altimetry products from November 2021 to October 2022 are assessed. The assessment contains synthetic aperture radar mode (SARM) as well as low-resolution mode (LRM) data. The <i>SSH</i> assessment is conducted using range noise, sea level anomaly (SLA) spectral analysis and crossover analysis, whereas the <i>SWH</i> and wind speed assessments are performed against NDBC buoy data and other satellite altimetry missions. The performance of the Sentinel-6 altimetry data is compared to those of Sentinel-3A/B and Jason-3 altimetry data. The 20 Hz range noise is 3.07 cm for SARM and 6.40 cm for LRM when <i>SWH</i> is 2 m. The standard deviation (<i>STD</i>) of <i>SSH</i> differences at crossovers is 3.76 cm for SARM and 4.27 cm for LRM. Compared against the NDBC measurements, the Sentinel-6 <i>SWH</i> measurements have a root-mean-square error (<i>RMSE</i>) of 0.361 m for SARM and an <i>RMSE</i> of 0.225 m for LRM. The Sentinel-6 wind speed measurements show an <i>RMSE</i> of 1.216 m/s for SARM and an <i>RMSE</i> of 1.323 m/s for LRM. We also present the impacts of ocean waves on parameter retrievals from Sentinel-6 SARM data. The Sentinel-6 SARM data are sensitive to wave period and direction as well as vertical velocity. It should be paid attention to in the future.