Sea State Bias Variability in Satellite Altimetry Data

Yongcun Cheng,Xiaofeng Li,Ting Liu,Bin Zou,Qing Xu,Le Gao

doi:10.3390/rs11101176

Abstract

Sea State Bias (SSB) contributes to global mean sea level variability and it needs cm-level range adjustment due to the instrumental drift over time. To investigate its variations and correct the global and regional sea level trend precisely, we calculate the temporal and spatial variability of the SSB correction in TOPEX, Jason-1, Jason-2 and Jason-3 missions, separately, as well as in the combined missions over the period 1993–2017. The long-term trend in global mean operational 2D non-parametric SSB correction is about −0.03 ± 0.03 mm/yr, which accounts for 1% of current global mean sea level change rate during 1993–2016. This correction contributes to sea level change rates of −1.27 ± 0.21 mm/yr and −0.26 ± 0.13 mm/yr in TOPEX-A and Jason-2 missions, respectively. The global mean SSB varies up to 7–10 mm during the very strong ENSO events in 1997–1998 and 2015–2016. Furthermore, the TOPEX SSB trend, which is consistent with recently reported sea level trend drift during 1993–1998, may leak into the determined global sea level trend in the period. Moreover, the Jason-1/2 zonal SSB variability is highly correlated with the significant wave height (SWH). On zonal average, SSB correction causes about 1% uncertainty in mean sea level trend. At high SWH regions, the uncertainties grow to 2–4% near the 50°N and 60°S bands. This should be considered in the study of regional sea level variability.

Highlights

TOPEX, Jason-1, Jason-2 and Jason-3 have provided 25-years of continuous and near-global coverage of sea level measurements
The error is on the order of a few tens of centimeters and it must be properly corrected in satellite altimetry data [3,4]
Compared with the results from Jason-1/2 mission, dramatic differences between zonally averaged Sea State Bias (SSB) trend and (−0.03 × significant wave height (SWH)) trend are found from TOPEX-A mission

Summary

Introduction

TOPEX, Jason-1, Jason-2 and Jason-3 have provided 25-years of continuous and near-global coverage of sea level measurements. The SSB combines an electromagnetic bias, a skewness bias, an instrument tracker bias, and compensates the bias of the altimeter range measurement towards the troughs of ocean waves It was originally modeled as a percentage of the significant wave height (SWH). To overcome the major drawback, several non-parametric SSB models have been developed to produce a predictor–response relationship directly from the regression data without imposition of a specific functional relation between the estimated SSB and the predictors, and the three-dimensional (3D) nonparametric models were developed using the wave period data from WAVEWATCH III [21,22] or ERA-Interim model [23] to account for the effects of wave development on altimetry sea level measurements. This work improved our understanding on the determination of GMSL trend in TOPEX and Jason-2 era

Data and Methods

Zonal SWH and SSB Trends

Findings

Discussion and Conclusions