Propagation Measurement and Statistical Characteristics of Evaporation Duct Channels in the Bohai Strait during November 2021

Evaporation ducts (EDs), functioning as natural atmospheric waveguides, can enhance maritime communication capabilities and thereby contribute to navigational safety in the Bohai Strait. However, the lack of field measurements in this region hinders accurate characterization of ED channels. To address this gap, a 22-day measurement campaign was conducted in November 2021, establishing two 111-km bidirectional microwave over-the-horizon (OTH) links. The measurements reveal stable channel reciprocity during Nov. 8-19. Statistical analysis indicates that for full measurement, the cumulative path loss (PL) probabilities below 190, 180, and 170 dB were 44.5%, 38.0%, and 22.0%, respectively. The bidirectional links exhibited minimal discrepancy during the overlapping period, suggesting a quasi-uniform ducting condition. Furthermore, evaporation duct height (EDH) inversion was implemented. Comparisons demonstrate that PL predictions relying on measured meteorology or ERA5 reanalysis data exhibit substantial deviations, while the inversion method achieves a significantly lower RMSE of 2.3 dB, underscoring its effectiveness. Finally, partial Spearman correlation analysis confirms that the EDH is predominantly driven by wind speed and relative humidity. These findings validate the feasibility of ED communications and provide critical reference data for system design in the Bohai Strait.