海面のマイクロ波放射の風速依存性

抄録

Effects of wind-generated roughness on the sea surface microwave emission at 6.7 and 18.6GHz are discussed in vertical and horizontal polarizations in angular range of incidence from 20f to 70 degrees, based on observed data. The sea surface brightness temperature (microwave temperature), employed for discussions on microwave emissivity, depends on the sea surface roughness generated by wind and developed with increasing wind speed. Then wind speed is adopted instead of the sea surface roughness. It is another reason for adopting wind speed that Cox and Munk have alredy reported that the rms slope of the sea surface is closely correlated with wind speed. Such wind speed sensitivity of microwave emission also depends on observational conditions such as frequency, incidence angle and polarization. The vertically polarized sea surface brightness temperature is insensitive to wind speed in the region of 53 degrees of incidence angle at both frequencies, however, this temperature increases below and decreases above this angle with increasing wind speed and larger wind-induced changes in brightness temperature are observed at lower and higher incidence angles at both frequencies. The horizontally polarized temperature is less dependent on incidence angle at both frequencies, but is more sensitive to wind speed than the vertically polarized one over the entire range of incidence angle except the regions of 20 and 70 degrees at both frequencies. Finally our results are compared with those already reported at several frequencies by many investigators. Wind speed sensitivities are rather different, but quite the same emissive characteristics are observed.