Sentinel-6 Delay-Doppler Altimetry Retracking 5 parameters

Type of dataset: Sentinel-6 L2P Products 

Digital Object Identifiers (DOIs):  10.24400/527896/AVISO-2026.008 - more metadata

Condition of access: This product is distributed by AVISO under standard AVISO+ license agreement.

Contents: 

Description: Operational altimetry processing traditionally relies on a “frozen sea” assumption, neglecting the influence of ocean dynamics on Doppler frequencies and introducing biases in estimated sea-state parameters. This dataset is based on an advanced SAR (Delay-Doppler) processing approach that overcomes this limitation by explicitly accounting for ocean surface dynamics. 
The methodology incorporates enhanced SAR models that jointly retrieve the standard deviation of vertical wave orbital velocities and the along-track component of the geophysical Doppler vector. These quantities are estimated through full two-dimensional retracking of unfocused SAR Delay-Doppler maps (stacks), rather than through the conventional summed Doppler beam approach used in operational processing. 
The processing has been implemented within the Sentinel Processing Prototype (SPP), leading to the generation of two six-month Sentinel-6A (S6A) data series covering January–June 2022 and January–June 2024. 

Validation results show that the dataset is fully consistent with conventional altimetry products in terms of sea surface height (SSH) and significant wave height (SWH), while providing reduced noise levels and improved along-track resolution. 
Key added-value parameters and improvements include: 

• Vertical wave velocity statistics: The dataset characterizes azimuth smearing induced by vertical wave motion, enabling the retrieval of the standard deviation of vertical wave velocity. This parameter is directly related to the mean zero up-crossing wave period and refines the estimation of sea-state conditions. Its inclusion reduces sea-state-dependent biases in SWH and shows strong agreement with ERA5 wave model outputs without requiring external corrections.
• Geophysical Doppler contribution: The along-track component of the geophysical Doppler vector is estimated, providing information linked to wind direction and intensity, as well as surface currents (including contributions such as Stokes drift). Accounting for this term significantly reduces wind-dependent SSH biases, particularly between ascending and descending passes, while preserving large-scale spectral content. 

This dataset constitutes a demonstration product designed for the scientific community, showcasing the potential of advanced SAR retracking techniques. It delivers enhanced-resolution altimetry measurements together with improved SSH and SWH estimates, wave-period-related diagnostics derived from vertical velocity, and geophysical Doppler information. These features open new perspectives for coastal ocean applications, surface current studies, and swell characterization. 

Geographic coverage: global.

Citation: "The Sentinel-6 Delay-Doppler Altimetry Retracking 5 parameters product was produced by CNES and CLS and distributed (restricted access only) by AVISO". CNES, & CLS. (2026). Sentinel-6 Delay-Doppler Altimetry Retracking 5 parameters product (Version 1.0) [Data set]. CNES. https://doi.org/10.24400/527896/AVISO-2026.008 "

Resources:

• User Handbook
• L. Rodet et al., “Leveraging Delay-Doppler altimetry for Enhanced Sea-State Characterization, OSTST 2026
• Amarouche, L. et al (2023). Analysis of waves dynamics impact on Sentinel-6MF delay/Doppler measurements. In Proceedings of the Ocean Surface Topography Science Team Meeting 2023, Puerto Rico, WV, USA, 7 November 2023-11 Novembre 2023, https://ostst.aviso.altimetry.fr/fileadmin/user_upload/OSTST2023/Presentations/IPC2023-Analysis_of_Waves_Dynamics_Impact_on_Sentinel-6MF_Delay_Doppler_Measurements.pdf
• Dinardo, S. et al. (2023). Sentinel-6 MF Poseidon-4 Radar Altimeter: Main Scientific Results from S6PP LRM and UF-SAR Chains in the First Year of the Mission.Advances in Space Research, 73(1), 337-375. https://doi.org/10.1016/j.asr.2023.07.030
• Rodet, L. et al. (2024). Applying new processing capabilities in the SPP chain for improving wave characterization from Sentinel-3 and Sentinel-6MF mission data. 2024 30 Years of Progress in Radar Altimetry Symposium
• Buchhaupt, C. et al. (2021). Impact of vertical water particle motions on focused SAR altimetry.Advances in Space Research,68(2), 853-874. https://doi.org/10.1016/j.asr.2020.07.015
• Buchhaupt, C. et al. (2023). Conditional sea surface statistics and their impact on geophysical sea surface parameters retrieved from SAR altimetry signals.Advances in Space Research,71(5), 2332-2347. https://doi.org/10.1016/j.asr.2022.12.034
• Buchhaupt, C. et al. (2023). Towards the Mitigation of Discrepancies in Sea Surface Parameters estimated from Low- and High-Resolution Satellite Altimetry. Remote Sensing, 15, 4206. https://doi.org/10.3390/rs15174206
• Marié, L. et al. (2024). On the Effects of Ocean Surface Motion on Delay-Doppler Altimetry. IEEE Transactions on Geoscience and Remote Sensing, 62, 1-25. https://doi.org/10.1109/TGRS.2024.3387667