Influence of the Semi-Permanent Low-Level Ocean Duct on Centimetre Wave Scatter Propagation beyond the Horizon

Abstract

SINCE 1949, the Admiralty Signal and Radar Establishment has conducted a number of short-term investigations on the propagation of centimetric radio waves over sea, at ranges well beyond the radio horizon. Some details of this work have been given recently by Joy^1,2. It has been shown that, at frequencies of about 10,000 Mc./s., the extra-diffraction signal-levels relative to free space are invariably some 10–15 db. lower than the corresponding levels at 3,000 Mc./s. at all ranges beyond the radio horizon. However, the signal attenuation-rate with distance is very similar at these two frequencies. The observed difference in signal-level is apparently inconsistent with available theories^3,4 of radio wave scattering in the troposphere, and Starkey et al. ⁵ have suggested that it provides support for the alternative theory of layer reflexions from refractive index discontinuities in the lower atmosphere.