. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 25 15 20 WIND SPEED (M/Sec) Fig. 4. Observed ratio of streaks to whitecaps versus wind speed. Application to Microwave Emissivity Measurement Over the Ocean Ross el al. [1970] and Nordberg el at. [1971] from data ob- tained in March 1969 have shown that Kw< the increase in the microwave brightness temperature with whitecap density at the nadir viewing angle, amounts to about 1°K for a 1% change in whitecap density at GHz. Whether this sa
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography 25 15 20 WIND SPEED (M/Sec) Fig. 4. Observed ratio of streaks to whitecaps versus wind speed. Application to Microwave Emissivity Measurement Over the Ocean Ross el al. [1970] and Nordberg el at. [1971] from data ob- tained in March 1969 have shown that Kw< the increase in the microwave brightness temperature with whitecap density at the nadir viewing angle, amounts to about 1°K for a 1% change in whitecap density at GHz. Whether this same figure is correct for the thin foam streaks (which may be largely a single-layered phenomenon at the surface) is not known exactly, although it would appear to be somewhat less. Williams [1971], investigating the phenomenon in a tank, reports that at 3-cm wavelengths the emissivity of foam- covered water is raised from to , the foam thickness be- ing only 3 mm. This finding would suggest that the streaks might be as important as whitecaps, at least at the higher microwave frequencies. However, it is possible that a streak visible with photography is not altogether a surface phenomenon but also includes light scattered from bubbles suspended just below the surface. If this is the case, streaks and foam patches would contribute less than whitecaps to changes in the microwave emissivity. In either case the streak contribution to the measured brightness temperature increase may be represented as some constant Ks multiplied by the ratio of the streaks to the whitecaps RSw- If the whitecap and streak sensitivities are represented in this manner, the change in brightness temperature due to foam may be related to the whitecap density according to the expression ATb — (Kw + RswKs) Ws (5) By means of the observations of A7"fl, Kw, and Ws obtained. Fig. 5. Surface analysis of meteorologic situation for the fetch limited experiment of January 27, 1971, at 1200 GMT. Isobar
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