Coherent and incoherent scattering of microwaves from the ocean

Abstract

This report, the third in a series, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1,2</sup> summarizes experimental studies of microwave over-ocean propagation on line-of-sight paths. Measurements at 5.3, 3.2, and 0.86 cm wavelength in 1955, in the Gulf of Mexico, between two oil drilling platforms one mile apart are compared with the results of the phenomenological model developed earlier. The total field was measured at maxima, and minima of the interference patterns using a sequence of receiver beam widths. The scattered field alone was measured by means of a narrow beam. The 1955, Gulf of Mexico data, are consistent with the previous 1953, Golden Gate data, in regions of overlap of certain parameters, and provide extended coverage for other values under different conditions. Specifically, some of the new findings are: a) The experimental values of the coherent reflected field are larger than exp [ <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2(2\pi h\psi /1000\lambda)^{2}</tex> ] for values of "apparent ocean roughness" ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h\psi/\lambda</tex> ) greater than 110 milliradians, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</tex> =standard deviation of water surface, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\psi</tex> =grazing angle in milliradians, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda</tex> electromagnetic wavelength, b) After rising from zero, the incoherent scattered power exhibits a downtrend for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h\psi/\lambda</tex> greater than 110. The incoherent power divided by the square of the smooth sea reflection coefficient shows no polarization dependence, c) The distribution along the surface as measured by the narrow-beam antenna shows that the coherent and incoherent power are markedly peaked in the specular direction, d) The ratios of coherent-to-incoherent power (m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) obtained from the shapes of the probability distributions agree with the power ratios obtained by measurements of the magnitudes of the signals, e) Total signal spectra broaden with increasing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h\psi/\lambda</tex> as found at the Golden Gate; the relative shapes of spectra agree with those from the Golden Gate. Horizontally- and vertically-polarized total signal spectra are the same.