Electromagnetic spectrum distribution prediction is the basis for the development of wireless communication technology. Due to the high randomness of the rough sea surface, it is difficult to accurately predict the offshore electromagnetic spectrum distribution. We present a prediction model of offshore electromagnetic spectrum distribution based on ray tracing method and Pierson-Moskowitz (PM) wave spectrum model. Based on the antenna attitude and the antenna directional pattern, the field strength calculation formulas of the electromagnetic wave sight line ray (SLR) propagation and the electromagnetic wave reflecting line ray (RLR) propagation off the sea surface are established. As the sea surface and the antenna attitude change, the effective rays from the transmitting antenna to the receiving antenna also change. This paper focus on the electromagnetic spectrum distribution prediction by calculating the effective angle (EA) of the transmitting antenna. We relate the EA to the antenna tilt angle and the antenna directional pattern, and combine the PM wave spectrum to establish the offshore electromagnetic spectrum distribution prediction models. Finally, we simulated the electromagnetic spectrum distribution prediction based on specific PM wave spectrum data. INDEX TERMS Offshore electromagnetic spectrum distribution, ray tracing, reflecting plane, directional pattern.

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