Investigation of diffuse multipath at low grazing angles

Abstract

<p>In the present thesis, an experimental database is used to investigate multipath, focusing mostly on the diffuse component. The experimental conditions cover the case of CW, coherently received microwave radiation, with a sampled aperture linear array, scattered at low-grazing angles, over the sea surface. A variety of frequencies covering the entire X-band and grazing angles were employed to explore the diffuse multipath structure.</p> <p>A new technique, Thomson's multiple-window-method (MWM), proves to be the proper tool for this experimental investigation. The following characteristics of diffuse multipath, for this particular class of experimental conditions, are extracted for the first time ever: <ul> <li>Amplitude statistics (1st order statistics). </li> <li>Complete wavenumber and frequency domain power spectra (2nd order statistics). </li> <li>Bispectra (3rd order statistics). </li> <li>Coherencies and transfer functions between channels at different frequencies and grazing angles. </li> <li>An improved method for estimating angles of arrival. </li> </ul></p> <p>Theory plays supportive role only, since the general problem of electromagnetic scattering from rough surfaces still remains to be solved. The main contributions from this research regarding diffuse multipath at low grazing angles are: <ul> <li>The shape of wavenumber/frequency domain power spectra. </li> <li>Confirmation that amplitude statistics for the Lpol channel are K distributed.</li> <li>The wavenumber/frequency domain bispectra indicate a non-Gaussian structure for the diffuse multipath component. </li> </ul></p> <p>Any theory that deals with microwave scattering, over the sea surface, at low grazing angles, how to take these findings into account.</p>