Polarimetric radar techniques for the measurement of ocean wave spectra

Azimuthally traveling waves are seldom well imaged in either real aperture radar (RAR) or synthetic-aperture radar (SAR) images of the ocean. Real aperture radar cross section modulation by long ocean waves is normally attributed to two principal sources, tilt modulation and hydrodynamic modulation. The effect of these modulations is described mathematically by a complex modulation transfer function. In ocean radar images both of these modulation sources roll-off to zero in the azimuthal direction. Therefore, complete two-dimensional k-space wave spectra derived from microwave data are often quite different than the physical ocean spectra. Evidence is presented to show that a new source for backscatter modulations will result when the linear polarization vector of the radar is optimized specifically to sense wave tilts occurring in the azimuthal direction. The improvement in the fidelity of 2D wave spectra created using optimized polarizations is investigated using a RAR ocean imaging mode