Abstract's details

Monitoring Sigma0 in the Sentinel era

Graham Quartly (Plymouth Marine Laboratory, United Kingdom)

Event: 2022 Ocean Surface Topography Science Team Meeting

Session: Instrument Processing: Propagation, Wind Speed and Sea State Bias

Presentation type: Type Forum only

Contribution: not provided


Over the ocean, an altimeter's sigma0 values are interpreted as a measure of local wind speed due to its effect on surface roughness. However, for climatological studies of possible changes in wind climate it is essential to have confidence in the stability of the calibration of a sensor and also in the relative calibrations of different sensors. Here I review the application of dual-frequency monitoring techniques applied to the Sentinel-3A and 3B altimeters and also to Jason-3 and Sentinel-6MF. The approach relies on the close relationship between scattering at the scales of interest for Ku- and C-band to offer a robust reference. Such an approach provides resilience even where there is an interruption in the series of altimeter satellites.

This technique was developed using the MLE3 estimates from LRM altimetry, but can be applied to MLE4 estimates of (P)LRM altimeters and other estimates from SAR altimeters once an adjustment has been made for these measures sensitivity to perceived mispointing. The peak of the sigma0-sigma0 curves, corresponding to a wind speed of about 6 m/s, is very robust to wave conditions, but significant wave height does have a marked impact on the relationship at very low wind speeds, with a lesser known effect at high wind speeds that is consistent across all the altimeters investigated. A moderate change is also seen to correlate well with sea surface temperature. Thus both wave height and SST may be expected to have an influence in future wind speed algorithms, especially with efforts to study wind changes in a warming climate.
Monitoring Sigma0 in the Sentinel era
Graham Quartly
Plymouth Marine Laboratory
United Kingdom