Special Sensor Microwave/Imager (SSM/I)

Oceanic Surface Wind Speed

Overview

Over calm ocean, the emissivity at SSM/I observation frequencies is very low, with only the effects of the intervening atmosphere (e.g., water vapor, clouds, and rain) causing a "warming" of the radiation measured by the satellite. The effect of increased wind speed is to "roughen" the calm surface through the formation of capillary waves and foam.

The net effect is to increase the emissivity and hence, the satellite measurement. The 37 GHz channels are the most sensitive to this phenomenon. However, the detection of wind speed variations are limited to mainly non- raining atmospheric conditions, as dense clouds and rain tend to mask the ocean surface. An algorithm developed by Goodberlet, et al (1989) was used to produce the monthly wind fields, which represent conditions at a 19.5 meter height.

The monthly mean near-surface oceanic wind speed is generated using the screening criteria given by Goodberlet et al., (1989), and is only produced under rain flag 0 and 1.

References

Goodberlet, M.A., C.T. Swift, and J.C. Wilkerson, 1989: Remote Sensing of Ocean Surface Winds with the Special Sensor Microwave Imager. J. Geophys. Res., 94, 14544-14555.