Prediction of Over-the-Horizon Electromagnetic Wave Propagation in Evaporation Ducts Based on the Gated Recurrent Unit Network Model

Evaporation ducts have a significant impact on electromagnetic (EM) wave propagation. The accurate prediction of EM propagation loss (PL) is important for the practical application of EM systems. However, the random weather processes and interaction of air-sea variables will cause complex spatial and temporal fluctuations in PL, especially for an over-the-horizon link. The physics prediction models show some limitations in practice. This article proposes a data-driven PL prediction method based on the gated recurrent unit network (GRU-PL). An X-band EM propagation system was developed and deployed for one month to collect PL of a 53 km link in the South China Sea for model training and testing. The GRU-PL model uses the air-sea variables as inputs and outputs the predicted PL. The root-mean-square error (RMSE) of the GRU-PL model is 7.04 dB, decreasing by 57.2% compared with the classical method. Furthermore, a method, which uses the inversion evaporation duct heights (EDHs) as the output to train the GRU network and then uses the parabolic equation model to predict the PL based on the GRU predicted EDHs, is also discussed. The RMSE is 7.3 dB. This method shows good potential in PL prediction of dynamically changing EM propagation links.