The dependence of microwave radio signal spectra on ocean roughness and wave spectra

This paper is an extension of previous work on reflection of microwaves from an ocean surface. The present analysis, dealing with spectra, is based on data obtained in a one-way -band propagation experiment performed across the Golden Gate, San Francisco. Two paths of 9000 and 15,000 feet were used. To describe the ocean surface, wave gages were mounted on a piling driven into the Golden Gate channel. Radio-signal spectra are found to be broader than the ocean-wave spectra and the spectral breadth a function of ocean roughness. The important result of this analysis is the establishment of a linear relationship between ocean roughness and the spectral breadth of the radio signals. Ocean roughness is measured by the product of the standard deviation of the wave height and the grazing angle divided by the radio-wave length. Radio spectral breadths are determined by the frequencies at which each spectrum drops to the 0.9-, 0.8-, 0.7-, 0.5-, 0.25-, and 0.l-power points. The breadths are then expressed as ratios of these frequencies to the frequency of the peak in the simultaneous ocean-wave spectrum. The analysis now enables one to predict the approximate shape of the spectrum of the radio signal received in a one-way transmission path given only a knowledge of the geometry, radio-wave length, ocean-wave height, and the peak frequency in the ocean spectrum.