CoAuthors

Stéphanie Urien (CLS, France); Emeline Cadier (CLS, France); Aude Bourdeau (CLS, France); Thomas Moreau (CLS, France); Laïba Amarouche (CLS, France); Robert Cullen (ESA, The Netherlands); Marco Fornari (ESA, The Netherlands); luisella Guilicchi (ESA, The Netherlands); Julia Figa Saldana (Eumetsat, Germany); Remko Scharroo (Eumetsat, Germany); François Bignalet-Cazalet (CNES, France)

The Sentinel-6 mission, also called Jason-CS, is part of the Copernicus program, which aims at continuing the Jason series of operational oceanography missions for the period 2020-2030. The main payload instrument of the mission is a dual-frequency Ku/C radar altimeter (Poseidon-4), evolving significantly from its predecessors (Poseidon-3A/3B carried on-board Jason-2 and Jason-3 satellites respectively). Among notable evolutions, Poseidon-4 will operate in an innovative interleaved mode emitting pulses in continuous and at relatively high repetition rate (9kHz). That way, conventional Low Resolution Mode (LRM) and Synthetic Aperture Radar (SAR) mode data can be generated simultaneously. In addition, as the number of independent looks increases, the measurement noise in SAR processed altimeter echoes is expected to be significantly reduced. For the sake of continuity with preceding missions, low- and high-resolution products will be generated from usual data processing, called baseline processors in LR and HR modes.
In the past four years, CLS has conducted the development of the level-2 ground prototype processor (GPP) under ESA contract and of the altimeter level-2 payload data acquisition and processing (PDAP) under EUMETSAT contract with Exprivia as prime contractor. These two developments have been carried out by two independent teams, also employing different technical solutions. The level-2 altimeter chain consists of two processors each of them enabling to generate geo-located geophysical retrievals from high- or low-resolution waveforms. Unlike the PDAP, however, the L2 GPP includes additional processors: LR-RMC, LR-OS and FF-SAR to experiment new innovative modes of measurement.
The level-2 GPP has been tested and validated using simulation data, and fully assessed with reconditioned Sentinel-3 data, thus demonstrating the high-reliability and robustness of the software, and its capability to be used as a good reference for the operational processing assessment. In addition, analyses have been carried out to assess new implemented algorithms, and the sensitivity of the retracked estimates to their parametrization.
This presentation describes the global validation strategy to fully assess both the prototype and the operational chain and the different analysis performed on new algorithms or adaptation: range compression, Samosa retracker fitting routine, and doppler beam sampling. These analyses enable us to make some recommendations for the Poseidon-4 processor parametrization which are provided in this presentation.