Identification and Reduction of Retracker-Related Noise in Altimeter-Derived Sea Surface Height Measurements

Abstract

AbstractData from the Jason-2 calibration/validation mission phase have been analyzed to identify the correlation between sea surface height (SSH) and significant wave height (SWH) errors. A cross-spectral analysis indicates that the SSH and SWH errors are nearly white and significantly correlated at scales from 12 to 100 km, consistent with the hypothesized error source, the waveform retracker. Because of the scale separation between the SWH signal and noise, it is possible to correct the SSH data by removing the SSH noise correlated with the SWH noise. Such a correction has been implemented using the empirical correlation found during the Jason-2 calibration orbit phase and applied to independent data from other phases of the Jason-1 mission. The efficacy of the correction varies geographically, but variance reductions between 1.6 and 2.2 cm2 have been obtained, corresponding to reductions of 20%–27% in the noise floor of along-track spectra. The corrections are obtained from and applied to conventional, 1 Hz, altimetry data and lead to improvements in the signal-to-noise ratio for identification of high-frequency narrowband processes—for example, internal tides—from these data.