Dual-polarized Ku-band backscatter signatures of hurricane ocean winds

The Ku-band dual-polarized backscatter signatures of ocean surfaces are des cribed in this paper with the airborne scatterometer measurements collected in the Hurricane Ocean Wind Experiment:in September 1997, The data collect ed from flights over:Hurricane Erika provide a direct evidence that there a re wind direction signals in the vertically and horizontally polarized Ku-b and backscatter of ocean surfaces under the influence of hurricane-force wi nds. At 46 degrees incidence angle, the vertically polarized backscatter ac quired at the upwind direction increases by about I dB as the wind speed in creases from 22 m.s(-1) to 35 m.s(-1), while the horizontally polarized bac kscatter appears to he twice as sensitive with a change of about 2 dB. At 3 5 m.s(-1) wind speeds, the difference between upwind and crosswind observat ions of vertically polarized backscatter is about 1.5 dB, smaller than the 2 dB difference for the horizontally polarized backscatter. This demonstrat es that the horizontal polarization has a greater sensitivity to wind speed and direction than the vertical polarization in the high wind regime. The data also suggest that the upwind and downwind asymmetry of Ku-band backsca tter decreases with increasing wind speed and can fall below 0 dB at small incidence-angles (<35 degrees) for the vertical polarization. A combined in teraction of the geometric optics scattering and the short wave modulation by long waves is proposed to interpret this phenomenonn and appears to agre e with the dependence of the signature on incidence, wind speed, and polari zation. The aircraft flight data-support the feasibility of dual-polarized Ku-band radar for hurricane ocean wind measurements, although the data do s uggest a reduced wind speed and direction sensitivity in the high wind regi me. Also, the differing polarization backscatter signatures suggest the rel ative contributions of various surface scattering mechanisms. An improved K u-band GMF is described.