THE EFFECT OF THE ROUGH AIR-SEA INTERFACE ON VERY-LOW-FREQUENCY AND EXTREMELY-LOWFREQUENCY PROPAGATION
NEW MEXICO UNIV ALBUQUERQUE ENGINEERING EXPERIMENT STATION
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The purpose of this investigation is to obtain an engineering understanding of the effect of the rough air-sea interface on electromagnetic signals used in communication to submerged submarines. The frequency of the electromagnetic wave is restricted to the ELF or VLF range. The fields on the air side of the sea surface are computed with the aid of the assumptions that the sea is a perfect electric conductor and that the sea surface is only slightly rough i. e., the maximum slope of the sea surface is much less than 1 . The integral equations governing the tangential magnetic fields are formulated and solved. The fields in the sea are computed by assuming the tangential magnetic field is continuous through the air-sea interface. The method used in these calculations is a numerical one based on finite differences. Both from the numerical solutions and a heuristic theory of propagation in the sea, it is seen that the perturbation of the fields caused by the roughness of the sea surface decays rapidly with depth if the sea wave wavelength is less than or the order of magnitude of the skin depth of the sea at the frequency considered if the sea wave wavelength is many orders of magnitude larger the skin depth, there is little decay at the depths considered of the perturbation, so that the phase and amplitude of the fields in the sea vary with the height of the sea vertically above them.
- Radiofrequency Wave Propagation