The dependence of nadir ocean surface emissivity on wind vector as measured with microwave radiometer

Global brightness temperature observations of TOPEX/Poseidon microwave radiometer (TMR) at 18, 21, and 37 GHz have been collocated with near-simultaneous SeaWinds wind vector data as well as with monthly sea surface temperature and salinity products. The combined data allow us to study the dependence of zenith-directed ocean surface emissivity, at each frequency, upon both wind speed and direction. Results show a clear two-branch wind speed dependence; weak and linear below 7 m s with an increase in sensitivity above that point. The observed emissivity also depends on the angle between the wind direction and TMR’s antenna polarization orientation, providing satellite confirmation of aircraft-derived results. There is little change in these wind vector dependencies with frequency.