The influence of oblique waves on the azimuthal response of a Ku-band scatterometer: a laboratory study

The authors conducted experiments in the large wind-wave tank at IRPHE to examine the influence of longer waves propagating at oblique angles to the wind direction on microwave backscattering. Measurements were made of wind, wave directional spectra, and cross sections from a 13.5-GHz scatterometer at 30/spl deg/ from nadir incidence angle. the authors characterize the scatterometric azimuthal scans with respect to the magnitude and the direction of the maximum backscattered power. Scans of solely wind waves are used to assess the effects of oblique waves, for which the scans yield trends that are related to the oblique-wave direction relative to the wind and the oblique-wave steepness. In particular, cross-section maxima are enhanced by oblique waves and the direction of maxima rotates from the wind axis toward the oblique-wave direction. These scatterometer data, in addition to other oblique-wave studies, led the authors to conclude that wind vectors produced from standard retrieval algorithms for scatterometers should be used with prudence in regions with significant veering winds, such as near meteorological fronts.