Abstract's details

Uncertainties in SSB modeling and impact on MSL

Sébastien Figerou (CLS, France)

CoAuthors

Ngan Tran (CLS, France); François Bignalet-Cazalet (CNES, France); Gerald Dibarboure (CNES, France); Craig Donlon (ESA, Netherlands)

Event: 2022 Ocean Surface Topography Science Team Meeting

Session: Quantifying Errors and Uncertainties in Altimetry data

Presentation type: Type Oral

Current operational SSB corrections are derived empirically and built up as look-up tables that describe the SSB amplitude as a 2D function of the SWH and the wind speed parameters, both directly measured by altimeters. Different aspects of the empirical determination have been improved through the years: statistical methods for the SSB modeling, ways to extract the SSB signals from the SSH data, and improvement in the sea state description to better describe in-turn the SSB behaviors, but no much work has focused on the documentation of its uncertainties. It’s the aim of this presentation.
This characterization will serve 3 different purposes:
- Choice of an optimum SSB solution to use in ground segment for flying missions to get accurate SSH data. Often a 1-year based solution is used after launch to update the SSH measurements, but is 1-year period an optimum value or is it necessary to cumulate more data to get a more stable SSB solution due to inter-annual variations?
- Optimization of the reprocessing workload requested for SSB computation during reprocessing phase for past missions. Often also a 1-year based SSB solution is computed within reprocessing exercise to improve/homogenize the SSH derivation with the latest GDR standards and the SSB correction applied but as said before some inter-annual variations can perturbate the representativeness of the dataset, such as El-Nino events for instance. The “best” solution might be to derive a SSB table from the entire mission but because of the work burden of the reprocessing of all the dataset, this is not the most common option. A compromise could be found and propose to the Agencies.
- Documenting the contribution of the sea state bias (SSB) and associated dual-frequency ionospheric corrections to the global sea level uncertainty budget by providing not only the uncertainty level of this source of error in SSH data but also how it propagates to the sea level rise estimate.
This study will assess the variability and stability of SSB solutions through ensemble mean and the provision of the spread of the ensemble members can be used to estimate uncertainty. Some recommendation in term of optimum configuration (period length, choice of ensemble members by more robust averaging methods, selection of ‘normal’ years, …) to mitigate errors on sea level rise monitoring and the impact of the SSB table choice in the MSL uncertainty budget will be provided.
 

Oral presentation show times:

Room Start Date End Date
Sala Grande Thu, Nov 03 2022,09:30 Thu, Nov 03 2022,09:45
Sébastien Figerou
CLS
France
sfigerou@groupcls.com