Spectral variation in the microwave emissivity of the roughened seas

Recently acquired microwave data obtained from the NASA CV 990 research aircraft have yielded variation of sea surface emissivity as a function of various parameters. Data acquired at a wavelength of 1.5 cm, horizontal polarization, agree with data obtained earlier by Nordberg et al. and Hollinger at nadir and 50 deg viewing angles respectively; the ratio of brightness temperature change to wind speed change was found to be approximately 1 K per meter per second over a wind speed range of 5 to 26 meters per second. Combining these recent measurements with the earlier measurements, it is evident that microwave radiometry can be used as a remote-sensing anemometer over all wind speed ranges of interest. Data analysis revealed that for nadir-viewing instruments, the ratio of brightness temperature change to wind speed change was approximately constant for the 0.8-2.8 cm wavelength range, about three-quarters of that value at 6 cm, and nearly zero at 21 cm. A model is proposed that is consistent with observations.