Uses microwave backscattering experiments to present a coherent picture of the ocean wave-radar modulation transfer function (MTF) based on composite surface theory, short-wave modulation, and modulated wind stress. A simplified relaxation model is proposed for modulation of the gravity-capillary wavenumber spectrum by long waves. It includes all airflow modulation effects in the response of the equilibrium spectrum to changes in the airflow. Thus the explicit modulation of individual source functions need not be known in order to calculate the hydrodynamic MTF. By combining this model of the hydrodynamic MTF with microwave measurements, the authors attempt to determine wind shear stress modulation caused by long waves. In order to extract the hydrodynamic MTF from the microwave data, they remove tilt and range change effects from the measured MTFs. The results show that the inferred hydrodynamic MTF is higher for H polarization scattering than for V polarization. Since this is impossible for the true hydrodynamic MTF, these results strongly indicate a problem with composite scattering theory. One explanation may be the effects of intermediate-scale waves suggested by Romeiser et al. (1993). Since these effects are much stronger for H polarization than for V polarization, they may explain the observed discrepancy and, if so, imply that V polarization return should yield an acceptable upper limit for the true hydrodynamic MTF. Thus they incorporate their V polarization results into the proposed model to estimate an upper limit for the wind shear stress modulation along the long-wave profile. They infer that the primary source of modulation of Bragg resonant waves depends strongly on Bragg wavenumber and windspeed.
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