Impact of Jason-2 Wind Speed Calibration on the Sea State Bias Correction

Abstract

Calibration of the wind speed is an issue not only for the provision of an accurate metocean parameter but also for the stability of the whole altimetry system across several flying missions. Wind speed is one of the parameters used to derive the sea state bias correction and therefore affects the sea surface height measurement. The analysis performed in this paper benefits from an in-house reprocessing exercise of 1 year of Jason-2 data with both the 3- and 4-parameter Maximum Likelihood Estimator (MLE-3, and MLE-4) retracking algorithms. It took into account the new altimeter characterization file that will be used in the upcoming official reprocessing activity to generate version C of the Jason-2 Geophysical Data Record products. Updated comparison of MLE-3 and MLE-4 data confirms that the MLE-3 algorithm gives less high-frequency variations in σ⁰. A calibration of the Jason-2 wind speed estimates has been performed based on a bias-adjustment of the radar backscatter data (+0.32 dB for MLE-3 data and +0.28 dB for MLE-4 ones) between Jason-2 and Jason-1. This allows us to re-assess the sea state bias differences between these two instruments from recomputed solutions and to show that there is no SSB difference between the two altimeters at cm-level.

Keywords:

• Jason-2
• Jason-1
• wind speed
• sea state bias
• nonparametric models

Acknowledgements

The authors wish to thank the three reviewers (Graham Quartly and two anonymous experts) who provided valuable comments that lead to produce a significantly more comprehensive paper than originally submitted. This work was performed within the SALP project supported by the Centre National d’Etudes Spatiales (CNES) in France.