Estimation of the sea state bias error budget for pulse-limited satellite altimetry

Abstract

Using an empirical, non-parametric sea state bias (SSB) modeling method, which was developed as a tool for SSB error analysis (Putnam, Alexa Forthcoming), we provide an error budget for overall SSB error, as well as the contributing sources of this error budget. The error analysis compares methods used to derive SSB models from observed altimeter measurements, collinear differences of measurements from adjacent repeat cycles, and methods using both collinear and crossover differences of measurements. Our error analysis reveals systematic error caused by ionosphere correction uncertainty in SSB models obtained from direct measurements, and wet troposphere correction uncertainty in SSB models generated using difference measurements. Results also expose a correlation to altimeter measurement error, with the backscatter coefficient accounting for over 20% of the SSB evaluation error and SWH accounting for approximately 50-60%. The error analysis presented here suggests SSB errors are lower than the often-used approximation of SSB error as 1% of SWH, except at SWH values less than 2 m where errors are likely larger. We find that increasing the pulse repetition frequency of the altimeter reduces SSB errors. The future for improving empirical, nonparametric SSB estimation primarily depends on improving measured SWH.

Keywords:

• Error
• satellite altimetry
• sea level
• sea state bias

Acknowledgements

This article is based on Chapters 4 and 5 of the author’s PhD thesis (Shilleh 2021) and is a companion to (Putnam, Alexa Forthcoming). The authors would like to extend their gratitude to Robert Leben and Jade Morton from the University of Colorado Boulder, as well as Ryan Hardy from the National Oceanic & Atmospheric Administration (NOAA) for their helpful discussions throughout the course of this research. We would also like to acknowledge Jean-Damien Desjonquéres for his work with the retracked Topex/Poseidon product.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The Jason-2 GDR-D altimetry data that support the findings of this study are openly available through https://www.ncei.noaa.gov/products/jason-satellite-products. The Topex/Poseidon GDR-F data product was provided the NASA Jet Propulsion Laboratory, and is planned to become publicly available at the end of October. Any reference or alternative variable models used for the error analysis that are not already provided in the data products are publicly available, or provided upon request.

Additional information

Funding

This research was supported by a contract with the Jet Propulsion Laboratory, California Institute of Technology. The work performed by Shailen D. Desai for this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Further contribution was made by the NASA Earth and Space Science Fellowship (award number 80NSSC17K0337).