The EUMETSAT Polar System-Second Generation (EPS-SG) mission will be deployed in the 2019–2020 timeframe in order to ensure continuity of the EPS observation missions, currently realized with the MetOp satellite series, to support operational meteorology and oceanography; in particular, for numerical weather prediction (NWP), climate monitoring and to develop new environmental services. The scatterometer (SCA) is one of the high-priority payload instruments to provide vector surface wind observations over the ocean, which constitute an important input to NWP, as well as valuable information for tracking of extreme weather events. The EPS-SG SCA shall offer observations with higher spatial resolution than those provided by ASCAT on board MetOp, operating at C-band and with VV polarization. Furthermore, addition of HH or VH polarization is considered as an option. Phase 0 industrial studies, addressing the complete system design, have taken place from 2008 to 2009. Two study teams, constituted, respectively by Astrium SAS and Thales Alenia Space Italy, have performed comprehensive analyses of the system requirements, tradeoffs of various concepts, and preliminary design of the selected concepts, which included both the single and dual satellite configurations. Three distinct SCA concepts were initially considered for tradeoffs: 1) fixed fan-beam concept with six fixed antennas; 2) rotating fan-beam concept with a single rotating antenna; 3) rotating pencil-beam concept. The first two concepts were further elaborated during Phase 0, and the fixed fan-beam concept was selected as baseline after a final tradeoff. For supporting the above instrument concept elaboration by the industrial study teams during Phase 0, the Royal Dutch Meteorological Institute (KNMI) has developed retrieval algorithms tailored to those concepts, derived from the ASCAT operational algorithms, and specific metrics to characterize the associated retrieval performance. The metrics used for- the present performance assessment were: 1) wind vector root-mean-square error; 2) ambiguity susceptibility; and 3) wind biases. The end-to-end performance evaluation makes use of an ensemble of wind fields as input having the mean climatology distribution, generates the output wind-fields which account for the measurement system imperfections and geophysical noise, and computes the performance metrics for comparisons. This paper describes the three SCA concepts as analysed in Phase 0 studies by the industrial study teams and summarizes the technical tradeoffs carried out. The performance metrics are described and applied to two of the concepts in order to compare their respective merits. It is shown that both concepts are able to meet the observation requirements of EPS-SG.
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