Effects of sea reflections on phase of arrival of line-of-sight signals

Continuous wave signals at 9.6 GHz were propagated over a 97-km overwater path extending from an elevation of 80 m to 3000 m mean sea level (MSL). Variations in phase of arrival of the signals received by antennas having and beam widths were recorded simultaneously. With the nominal path elevation angle of , the broad-beam antenna received a contribution reflected from the sea surface, while the narrow-beam antenna largely discriminated against such reflections. The spectra of phase variations for the two cases were compared, and their coherency was computed. The broad-beam signal displayed consistently higher spectral density than did the narrow-beam signal over the fluctuation frequency range from 0.1 Hz to the limit of the analysis at about 10 Hz. The relatively large effect of multipath phase noise on range rate measurements is discussed.