Regional changes in Ka-band SSH related to influence of SST and mean wave period on altimeter backscatter coefficient

Ngan Tran (CLS, France)

CoAuthors

Doug Vandemark (UNH, United States); François Bignalet-Cazalet (CNES, France); Gerald Dibarboure (CNES, France); Nicolas Picot (CNES, France)

Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)

Session: Quantifying Errors and Uncertainties in Altimetry data

Presentation type: Type Forum

Global mean sea level (GMSL) climate record from altimeter missions required ancillary corrections to the instrument measurements to properly account for instrument and geophysical effects on the derived sea surface heights (SSH). In the various attempts to further reduce the uncertainty in altimeter-era climate data record, the sea surface temperature (SST) effect on satellite radar ocean backscatter data (s0) has been so far neglected while the s0 behavior modifies the SSH values through wind speed retrieval used for the sea state bias (SSB) correction estimations.
Vandemark et al [2016] reported that ocean s0 at Ka-band varies by nearly 15% between the coldest and the warmest ocean temperatures because of Fresnel reflection coefficient variation with SST. Such small but systematic SST dependent effect may require consideration prior to s0 use. They notably showed that significant improvement in ALTIKA ocean wind speed inversions based on a 1D model is obtained after applying some SST correction adjustment. Another ancillary parameter that could be considered to improve wind speed retrieval has been highlighted in Jiang et al [2020], this parameter is the mean wave period. In addition to significant wave height (SWH), the mean wave period also modulates the s0 behavior probably due to the tilting modulation of long-waves on the sea surface.

The purpose of this presentation is to report on the wind speed error related to both the SST and mean wave period effects on Ka-band s0. Then some preliminary impact evaluations of the single SST effect on SSB corrections will also be showed. Because of large regional SST variations, it seems important to evaluate its potential impact on the regional MSL estimates. This issue may become more important as altimeter records are extended in the future and effects of ocean warming become larger.
 
Ngan Tran
CLS
France
ntran@groupcls.com