Abstract's details
External Calibration Cross-Validation of Sentinel-6B and Sentinel-6 Michael Freilich During the Tandem Phase
Event: 2026 Sentinel-6 Validation Team meeting
Session: S6VT plenary session
Presentation type: Oral
Sentinel-6B was launched in November 2025 and entered a tandem configuration with Sentinel-6 Michael Freilich (S6MF) during its commissioning phase. In this configuration, both satellites follow the nominal Sentinel-6 reference orbit, with Sentinel-6B positioned a few seconds behind S6MF, enabling near-simultaneous acquisitions over the same ground locations. This tandem phase provides a unique opportunity for direct cross-validation of the two Poseidon-4 altimeters under identical geophysical conditions.
In this work, we present a detailed comparison of the external calibration performance of Sentinel-6B and S6MF using a network of transponders and corner reflectors. The analysis covers the full set of calibration sites used in the Sentinel-6 ground processing prototype: the CDN1 transponder (Crete, descending passe), the GVD1 transponder (Gavdos, ascending and descending passes), the CRM1 corner reflector (Montsec, ascending passe) and complementing it with passes over the rest of the corner sites available (Uscla, Cerdanya, Crete). The dataset spans from the beginning of the tandem phase in late December 2025 through June 2026, providing approximately six months of collocated measurements.
The calibration analysis focuses on the estimation and comparison of key performance parameters for both altimeters: range bias, datation bias, and, where applicable, sigma0 bias. In addition, the point target response (PTR) is characterised at each site to assess the impulse response quality in both the across-track and along-track directions. Associated metrics such as peak sidelobe ratio (PSLR), main lobe width, and sidelobe ratio are evaluated for each pass and compared between the two instruments.
Preliminary results based on data acquired through early February 2026 show consistent behaviour between both altimeters across all calibration sites. Range bias differences between S6MF and Sentinel-6B remain below 0.5 cm at CDN1, GVD1 ascending, and CRM1, while at GVD1 descending both instruments exhibit a comparatively larger absolute bias that is nevertheless consistent between them. Datation bias values are within the expected uncertainty, and PTR metrics confirm that the impulse responses match the theoretical expectations. The full analysis to be presented will extend the dataset to June 2026, significantly increasing the number of passes and the statistical robustness of the cross-validation results.
These results confirm that the Sentinel-6B Poseidon-4 altimeter is operating as expected and that its external calibration performance is consistent with that of S6MF. This cross-validation supports the transition to operational status and the continuity of the Sentinel-6 reference altimetry record.
Back to the list of abstractIn this work, we present a detailed comparison of the external calibration performance of Sentinel-6B and S6MF using a network of transponders and corner reflectors. The analysis covers the full set of calibration sites used in the Sentinel-6 ground processing prototype: the CDN1 transponder (Crete, descending passe), the GVD1 transponder (Gavdos, ascending and descending passes), the CRM1 corner reflector (Montsec, ascending passe) and complementing it with passes over the rest of the corner sites available (Uscla, Cerdanya, Crete). The dataset spans from the beginning of the tandem phase in late December 2025 through June 2026, providing approximately six months of collocated measurements.
The calibration analysis focuses on the estimation and comparison of key performance parameters for both altimeters: range bias, datation bias, and, where applicable, sigma0 bias. In addition, the point target response (PTR) is characterised at each site to assess the impulse response quality in both the across-track and along-track directions. Associated metrics such as peak sidelobe ratio (PSLR), main lobe width, and sidelobe ratio are evaluated for each pass and compared between the two instruments.
Preliminary results based on data acquired through early February 2026 show consistent behaviour between both altimeters across all calibration sites. Range bias differences between S6MF and Sentinel-6B remain below 0.5 cm at CDN1, GVD1 ascending, and CRM1, while at GVD1 descending both instruments exhibit a comparatively larger absolute bias that is nevertheless consistent between them. Datation bias values are within the expected uncertainty, and PTR metrics confirm that the impulse responses match the theoretical expectations. The full analysis to be presented will extend the dataset to June 2026, significantly increasing the number of passes and the statistical robustness of the cross-validation results.
These results confirm that the Sentinel-6B Poseidon-4 altimeter is operating as expected and that its external calibration performance is consistent with that of S6MF. This cross-validation supports the transition to operational status and the continuity of the Sentinel-6 reference altimetry record.