Abstract's details
An Analysis of the Sentinel-6A/B Tandem Phase Using an Improved Antenna Pattern and Stack Retracking
Event: 2026 Sentinel-6 Validation Team meeting
Session: S6VT plenary session
Presentation type: Oral
The launch of Sentinel-6B in November 2025 initiated a tandem phase with its predecessor Sentinel-6 Michael Freilich (Sentinel-6MF), during which both satellites operate with an approximately 30-second temporal separation for about one year. This configuration provides a unique opportunity for a direct intercomparison of sea-level and sea-state observations acquired by the two synthetic aperture radar (SAR) altimetry missions. Such a tandem phase is particularly valuable for assessing the consistency between both missions and for evaluating improvements in geophysical parameter retrieval approaches.
In this study, we apply an improved numerical retracking approach that allows the use of an arbitrary antenna pattern. Based on this framework, SAR waveform numerical retracking is performed to estimate key geophysical parameters including sea surface height (SSH), the radar backscatter coefficient, and significant wave height (SWH). The flexibility of the numerical model allows a more accurate representation of the point target response, and the antenna gain function, improving the accuracy of the parameter estimation. In addition to SAR waveform retracking, we perform stack retracking to retrieve further information contained in the Doppler beam stack. This approach enables the estimation of additional parameters such as the standard deviation of vertical wave particle velocities as well as the mean line-of-sight velocities observable by the radar altimeter. Incorporating these parameters directly within the retracking process helps mitigate errors in SSH and SWH that would otherwise need to be corrected during post-processing using lookup tables.
Both the SAR waveform retracking and the stack retracking approaches are applied to Sentinel-6MF and Sentinel-6B data using the TERP-SAR processor prototype, which starts at the input level-1A to generate level-2 data containing the geophysical parameters retrieved over the satellite track. The analysis covers as much data from the tandem phase as possible to provide a comprehensive assessment of the consistency between both missions.
Back to the list of abstractIn this study, we apply an improved numerical retracking approach that allows the use of an arbitrary antenna pattern. Based on this framework, SAR waveform numerical retracking is performed to estimate key geophysical parameters including sea surface height (SSH), the radar backscatter coefficient, and significant wave height (SWH). The flexibility of the numerical model allows a more accurate representation of the point target response, and the antenna gain function, improving the accuracy of the parameter estimation. In addition to SAR waveform retracking, we perform stack retracking to retrieve further information contained in the Doppler beam stack. This approach enables the estimation of additional parameters such as the standard deviation of vertical wave particle velocities as well as the mean line-of-sight velocities observable by the radar altimeter. Incorporating these parameters directly within the retracking process helps mitigate errors in SSH and SWH that would otherwise need to be corrected during post-processing using lookup tables.
Both the SAR waveform retracking and the stack retracking approaches are applied to Sentinel-6MF and Sentinel-6B data using the TERP-SAR processor prototype, which starts at the input level-1A to generate level-2 data containing the geophysical parameters retrieved over the satellite track. The analysis covers as much data from the tandem phase as possible to provide a comprehensive assessment of the consistency between both missions.