Improvements to estimating the air-sea gas transfer velocity by using dual-frequency, altimeter backscatter

Air–sea gas exchange is affected by sea surface roughness and a previous study shows a significant relation between Ku-band backscattering from satellite altimeters and field estimates of gas transfer velocity, K. Recently C-band backscatter data were made available for altimeters on board the JASON-1 and JASON-2 satellites. In this paper we used experimental data from the same cruises to show that using the difference between the Ku-band and
C-band signals to estimate sea surface roughness, and thus reducing the contribution fromlongerwaves, improved the K estimates. This is consistent with the theory that gas transfer is largely controlled by short capillary-gravity
waves. For satellite data closer than 2 hr and 0.5° from the K sample stations, the dual-frequency parameterization is found to perform better than a wind speed parameterization that uses in situ wind speed. The improvement
supports the hypothesis that gas transfer is more directly related to surface roughness than to surface wind.