Michel Guerra (isardSAT, Spain); Alba Granados (isardSAT, Spain); Mònica Roca (isardSAT, Spain); Albert García-Mondèjar (isardSAT, Spain); Ester Vendrell (isardSAT, Spain); Marco Fornari (ESA-ESTEC, Italy)

Sentinel-6B, launched on 16 November 2025, is currently being assessed during its commissioning phase through dedicated calibration and performance monitoring activities. Within the Sentinel-6 GPP project, isardSAT has monitored the Sentinel-6B Poseidon-4 radar altimeter, with emphasis on the evolution of key internal calibration parameters.
This contribution presents the current status of Sentinel-6B Poseidon-4 monitoring, both as a standalone assessment and through comparison with Sentinel-6 MF. The tandem phase provides a particularly valuable framework for evaluating inter-mission consistency under closely comparable conditions and for supporting the continuity of the reference altimetry record.
The analysis focuses on several internal calibration parameters, including internal delay, power, point target response (PTR) width, burst power and phase corrections, end-to-end distortions, attenuation tables (ATT), CAL2 shape, and ultra-stable oscillator (USO) frequency. Their temporal evolution and stability are analysed in order to identify possible anomalies, assess instrument compliance with respect to mission requirements, and highlight similarities and differences between Sentinel-6B and Sentinel-6 MF.
The results provide an overview of Sentinel-6B Poseidon-4 performance during commissioning and illustrate the value of the tandem phase for calibration/validation activities and for the assessment of inter-mission consistency, supporting the transition from Sentinel-6 MF to Sentinel-6B as the reference mission.