Microwave backscatter spatial variations in response to low winds and ocean fronts

Comparisons among measurements of sea surface Ku-band backscatter (dual polarized), wind speed, air and sea temperatures and friction velocity, heat and moisture fluxes were made from a manned airship platform off the Oregon coast in October 1993 during a month long field experiment. The broad objective of the experiment was to observe air/sea interactions with high spatial resolution and temporal coincidence of numerous sensors, in a coastal environment. The blimp platform enabled the measurements of surface conditions that displayed rapid spatial variations along its path. Among the most interesting observations were the frequent large amplitude drops and rises of the azimuthally averaged radar cross section (between 20/spl deg/ and 50/spl deg/ incidence angles) associated with wind variations in the range from 1 to 4 m/s. These observations demonstrate a minimum wind speed threshold for wave generation, which is being measured on the ocean for the first time after having been studied previously only in indoor wave tanks.